ECOLOGY AND BIOLOGY OF EGRETS WITH SPECIAL REFERENCE TO Egretta alba, E. intermedia, E. garzetta AND Bubulcus ibis IN AND AROUND ALIGARH
ABSTRACT
THESIS SUBMITTED FOR THE AWARD OF THE DEGREE OF Bottor of $l|Uoi^opt)p IN WILDLIFE SCIENCE
BY FAIZA ABBASI
DEPARTMENT OF WILDLIFE SCIENCES ALIGARH MUSLIM UNIVERSITY ALIGARH (INDIA) 2004 .^ ^'i^ itii;- INTRODUCTION There are 60 species of Ardeids comprising of herons, bitterns and egrets, which occur in most parts of the world. The name Egret comes from the French 'aigrette' meaning the plume feathers of the six species of white Egrets acquired during the breeding season. Egrets are large showy birds readily seen in most neighbourhoods and well appreciated by humans. They often nest on houses and in city parks and feed in pastures, meadows, flooded plains and along drains in towns. They also serve important ecosystem functions such as accelerating nutrient cycling at feeding grounds and regulating fish population. Although a general assumption is such that egrets are not in danger of extinction, baseline data for future conservation is essential as the lack of ftmdamental knowledge makes it difficult to pronounce upon ecological and economic status of most avian species (Hartley, P.H.T., 1948. Ibis 90:361-362). In the west detailed studies are available to serve the purpose but parallel data in India is scanty. This study was undertaken to explore the ecology and biology of four sympatric species of egrets largely focusing on aspects of niche overlap, resource partitioning measures and mechanisms of ecological isolation adapted by the species to maintain coexistence. Sheikha Lake in Aligarh District of Uttar Pradesh in the Upper Gangetic Plains of north India is a small wetland where the following four species of egrets are found:
Great White Egret Egretta alba Linneaus (GE) Intermediate Egret Egretta intermedia Wagler (ME) Little Egret Egretta garzetta Linnaeus (LE) Cattle Egret Bubulcus ibis Linneaus (CE)
Stemming from the classical work of Gausse (1934) community ecologists have long sought to understand how coexisting species utilize common resources such as food, space or time. Theories on the natural regulation of species diversity in communities are aimed at refining the concept of the species niche (Schoener 1974). A species niche is defined as the position of a species in a community, for example its use of food resources,
1 time of activity, location, mode of interaction with other species and so forth. The first is differential resource utilization or resource partitioning, which can be observed when species living in precisely the same habitat nevertheless exploit different resources (Lack 1971). He further illustrates that such ecological isolation brought about through competitive exclusion is of basic importance in the origin of new species, adaptive radiation, species diversity and composition of faunas. Earlier Darwin (1859) drew attention to the importance of competition for resources, which are not adequate for the survival of all the individuals bom. Big size differences between congeneric and sympatric species of birds are a means of ecological isolation (Huxley 1942).
OBJECTIVES Considering the above hypothesis the focus of the present study is to quantify niche differentiation mechanisms amongst four sympatric species of egrets. The following objectives were set to be achieved 1. To ascertain the status and populations of the four species of egrets within the intensive study area. 2. To analyze the partitioning of resources in micro habitat use of sympatric egret species 3. To study the variations in roosting patterns and roost-site selection amongst the sympatric egrets. 4. To depict their inter and intra-specific competitive spacing mechanisms. 5. To investigate their differences in food selection and use of foraging behaviour. 6. To quantify their various activity patterns - seasonal as well as diurnal.
ORGANIZATION OF THE THESIS
Chapter 1. Consists of a general introduction of the species, the concept of niche partitioning and comparative ecology and throws light on the rationale, objectives and background of the study. Chapter 2: Provides detail information on the geographical, physiographic, climatological and biological status of the intensive study area. Chapter 3: Quantification of micro-habitat utilization patterns, comparative abundance and interspecific associations of the four sympatric egrets have been discussed in this chapter. Comparisons have been made to testify differentiation on spatial scale. Chapter 4: In this chapter data has been presented on the food and foraging behaviour of the four species and degree of overlap in their dietary spectrum and foraging behaviours has been analyzed. This explains resource partitioning between the four sympatric species of egrets based on one of the most important resources i.e. food and foraging techniques. Chapter 5: Considering that time of a particular activity chosen by a species is of paramount survival value for coexisting species the measures of temporal distribution have been tested in this chapter. Juxtaposition of time and activity budgets of the four species, existing variations amongst them and changes occurring in them over time - be it season or time of day, have been described. Chapter 6: Since the communal roosting behaviour in colonial water birds is an important niche dimension, comparisons in the individual roosting patterns, and roost site selection based on ecological features amongst the four sympatric species of egrets have been done in this chapter. Summary and recommendations: In an endeavor to revisit some ecological questions some answers were endorsed during the present study while some remained unattended due to certain limitations. In this chapter a summary of future research directions indicated by this work has been given along with a brief outline of identified conservation oriented aims and measures to protect this important wetland.
METHODS The study was launched in August 2000 and field data collection followed in the beginning of 2001 after an initial literature survey and designing of the program. Data collection ended in March 2004. To study the behaviour and ecology of egrets focal animal sampling (Altman 1973) was done by dividing the each field day into three shifts of foiir hours each. The morning shift was fi-om060 0 hrs to 1000 hrs, the noon shift was fi-om 1000 hrs to 1400 hrs and the afternoon shift ranged fi-om 1400 hrs to 1800 hrs. The ftjcal animal was observed for the entire duration of a shift with the help of 8 x 40 binoculars from the close distance depending on the field conditions. The data of the entire study period was pooled together and divided into three seasons namely winter, summer and monsoon for analysis and interpretation. Equal number of four-hourly shifts were considered for analysis and discussions. To study the foraging behaviour and general activity patterns of egrets the starting and ending time of different general activities were noted, only if a particular activity was carried out for more that 15 seconds by the bird. Time budgets of the four species were compared with One-way ANOVA and Kruskall-Wallis test was used to see whether a species behaved differently between three shifts of the day and in three seasons. While the individual was found foraging its various activities extent of that particular behaviour and food items were recorded. Levin's measure of niche overlap was used to estimate the extent of overlap between the four species. Horn's index of niche diversity was used to quantify the foraging niche diversity of each species. To estimate the spatial distribution of egrets three trails were marked in the study area that covered the wetland, adjoining forests, ponds and crop fields where egrets were seen regularly. Trails were monitored on alternate days in different four-hourly shifts and counts of total number of individuals of each of the four species seen were maintained. For each encounter habitat type, water depth, vegetation cover and group size were recorded. Other avian species present in the habitat were also recorded. Student t-test was used ascertain the difference between the comparative abundance of four species. Chi- sqaure contingency analysis was done to test the associations of the species and habitat types as well as habitat parameters. Morisita's index of similarity was used to quantify the degree of overlap between the habitat use of four species and Shaimon-Weiner's measure was used to estimate the niche breadth of each species. The Cluster analysis was done to see the inter- and intra-specific species associations of egrets and other wetland species. The roosting patterns were studied by making observations at the roost site either in the morning (departure time) or in the evening (arrival time) at an alternate basis. Total time taken in settling, (mean arrival) or emergence (departure time) and pre-and post roosting behaviours were also recorded. Details of roost site characteristics were also noted. Pearson product moment correlation was used to ascertain the correlation between independent environmental variables like sunset and sunrise time and the dependent variables like emergence time and settling time. The Mann-Whitney U Test was used to determine the difference in the roosting behaviours and the roost site selection of the four species. All the analysis was done with the help of the statistical package SPSS 11.0 and FORTRAN based computer program NICHE.
RESULTS Spatial Distribution The population estimates of four species of egrets show that the cattle egret was present in largest numbers followed in decreasing order by the median egret, great egret and the little egret. Analysis of comparative abundance of the four sympatric species of egrets reveals that highly significant differences existed in the population sizes of CE-LE at t = 37.4, P<0.05, CE-ME t = 3.04, P<0.05, CE-GE t = 99.3, P<0.05, LE-ME t = 87.8, P<0.05, ME-GE t = 79.1, P<0.05 and LE-GE at t = 17.9, P<0.05 level of significance. Significant associations existed between the species and the habitat types. The cattle egret used a variety of habitat types both aquatic and terrestrial but preferred freshly upturned soil of the ploughed crop fields and dry grassland amongst terrestrial habitat types. Amongst the aquatic types it preferred reedbeds with low height vegetation growth and irrigated paddy fields {x^ = 213.6, P<0.05, df = 288). The little egret {x^ ^ Til.l, P<0.05, df = 288) mostly remained in open sheets of water within the lake and at the shore. Amongst its less preferred ventures into the terrestrial area it remained in short grasslands. The median egret however, showed high preference for reedbeds {x^ 139.1, P<0.05, df = 288) and made equal use of paddy fields, lake shore and marshes. The Great
AS egret (x = 297.3, P<0.05, df = 288) seems to have specialized in open water feeding as it uses the clear sheet of water within the lake and other pools. The cattle egret prefers to remain in shallow reaches when feeding in water and treads over vegetation, while the little egret and the median egret mostly stay in water up to 30 cm deep. Owing to its longest legs the Great Egret is the only species, which ventures up to 70 cm deep waters. The cattle and the median egrets fed in highly vegetated areas while the little egret and the large egret foraged in scantily vegetated areas. The cattle egret frequented the wetland when the stretch of water was less than 50% while for the little egret preferred stretch of water was more than 25%. The median egret frequented the Lake when the stretch was up to 75% and the great egret fed in the Lake when the stretch was more than 50% and even when the Lake was over flowing due to heavy rains. The egrets selectively utilized categories of ground vegetation cover; the cattle egret frequented areas only where it was more than 30%, whereas the little egret favoured areas with less than 30% ground vegetation. The median egret did not exhibit significant association with ground cover but the great egret showed significant preference for ground vegetation cover up to 60%. While the cattle egret was mostly found feeding away from the lake,the little egret maintained strict proximity to the Lake area. The median egret did venture away from the Lake but remained within a distance of about one kilometer. The great egret fed only in the close vicinity of the lake and its adjoining pools. Estimation of the habitat niche breadth of the four species shows that the cattle and the median egrets used a wide spectrum of habitat types: the great egret used a lesser diversity of habitat types and smaller niche breadth followed by the little egret. Analysis of niche overlap between the species indicates maximum habitat overlap between the Little Egret and the Great Egret. The Cattle Egret had near negligible overlap with any of the species for all habitat parameters. The Median Egret showed moderate overlap with Little Egret and Great Egret. Egrets have specific associations with other species of the waterfowl community when the entire wetland is considered as one guild. The community could be classified into two major clusters - 'A' and 'B'. 'A' consisted of the four species of egrets and the other resident waterfowl. The second cluster 'B' mainly consisted of the winter visitors. Frequency of visits of the egrets to the wetland for the purpose of foraging was impacted by the presence of other species. While the egrets frequented the wetland almost always in the presence of resident species, migratory waterfowl present in the Lake caused minor deterrence for egrets. With respect to frequency of utilization of the Lake, little egret maintained close proximity with the median egret (30.00) amongst sympatric species and to the white- breasted kingfisher and with the pond heron (36.00) amongst non-sympatric species. The median egret showed a reverse relationship with the little egret but its proximity to non- sympatric individuals differed with the latter as it was closest to red-wattled lapwing (23.00), pond heron (22.00) and black drongo (27.00). The great egret and the cattle egret were the proximate species amongst the sympatric group for each other at (31.00) and for the great egret the closest non-sympatric species were the black-winged stilt and the red- wattled lapwing at 21.00. For the Cattle Egret in terms of sharing the wetland on number of occasions, the nearest non-sympatric species is the white-breasted-kingfisher at 27.00.
Food and Foraging Associations between the species and the various foraging behaviours are highly significant. Cattle Egrets used a variety of feeding behaviours with walking slowly, standing and walking quickly most often {x^ ^ 32.7, P<0.05, df = 21) and Little Egrets used walking quickly and foot stirring most often, {x^ = 33.4, P<0.05, df = 21). The behaviour of foot stirring was unique to the Little Egrets. The Median Egrets used walking slowly most often but gleaning, probing and pecking and standing were also used with an equal thrust {x^ = 37.9, P<0.05, df = 21). The Great White Egret almost specialized in walking slowly and standing behaviour {x^ ^ 34.3, P<0.05, df = 21) with miniscule use of probing, pecking and chasing. The cattle egrets preyed upon terrestrial insects and small vertebrates such as amphibians, molluscs and crustaceans most often {x^ ^ 44.5, P<0.05, df = 30). The Little Egret fed mostly on small fish and its food also included crustaceans, amphibians and aquatic insects (x ^ =48.9, P<0.05, df = 30). The Median Egret most often fed upon small fish but larger fish and aquatic insects too formed a considerable portion of its diet (X ^ = 46.2, P<0.05, df = 30). The Great Egret almost exclusively fed upon larger fish, which constituted more than one half of the diet (x ^ = 43.8, P<0.05, df = 30). Cattle Egrets subsisted on smaller prey of less than 6 cm (x ^ = 22.8, P<0.05, df = 12), prey size of the little Egret ranged from 2 cm to 8 cm (x^ = 27.1, P<0.G5, df = 12). Median Egret preyed upon intermediate size fish and crustaceans less than 8 cm in size {x^ ^ 25.2, P<0.05, df = 12) but the Great Egret maximized on fish larger than 8 cm iX^ ~ 24.7, P<0.05, df = 12). However, since they eat small fish too some of their prey was less than 6 cm. The measurement of niche breadth indicates that Cattle and Median egrets used almost the same diversity of foraging behaviors whereas the little egrets used only walking quickly and foot-stirring. The Great Egret used walking slowly and standing.
Temporal distribution Pertaining to different behavioural traits interspecific differences were significant amongst the sympatric egrets. Each species was also found adjusting its time and activity budgets corresponding to the different shifts of the day and different seasons. The largest share of the time budget was occupied by the time spent in foraging - the little egret spent 68% time in foraging followed by cattle egret (66%), median egret (58%) and great egret (54%). This foraging time increased by 5% in winters and 10% in monsoon. The sympatric egrets were also found devoting less time to foraging in the afternoon and more time in the morning and evening. However, statistically significant differences were found by multiple comparisons in the foraging activity of all the species. While the Little and the great egrets spent more time foraging in the morning the cattle egret maximized on this activity in the evening. The Median egret made equal use of both the shifts for foraging. In winters the largest time spent on foraging was by the cattle egret followed by little egret, great egret and median egrets in descending order. On the contrary patterns changed during summers when the great egret spent maximum time foraging followed by the cattle egret, little egret and median egret. This pattern was again
8 redesigned for the monsoon when the Httle egret spent most time foraging followed by cattle egret, great egret and median egret. The non-foraging activities of the four species partly consisted of maintenance activities like preening, resting, siesta and miscellaneous events. More time was devoted to these activities by all species in the noon and afternoon hours. Significant difference was found between the four species for time allocation to these events. While the little and the cattle egret spent less time in these activities the median and the great egret devoted more time to preening and resting. A small portion of the time and activity budget was devoted to interactive events of display and chasing. While median and great egrets differed in their display behaviour in winters, during summers all the species differed in display time allocation. Significant difference existed in display time between little and great egrets for the noon shift. Chasing time allocation differed between little and median egrets for the morning shift and between cattle and little egrets for the afternoon shift.
Roosting behaviour The roosting of sympatric egrets was found to vary in different seasons as it is largely governed by the time of sunrise and sunset. The egrets began to emerge approximately one hour before sunrise and continued to do so up to 15 minutes after sunrise. Arrival of the species to the roost sites for settling was also positively correlated with the time of sunset (for Cattle Egret r = .980 at P = 0.01, for Little egret r = .996 at p = 0.01, for Median egret r = .966 at P = 0.01 and for Great Egret r = .899 at P = 0.01;) on the basis of which we can interpolate the statistical conclusion that the correlation between arrival of egrets at the roost sites with that of the time of sunset is highly significant. Arrivals began about ten minutes before sunset and continued for about half an hour after sunset until all four species had arrived. A negative correlation has been foimd between the total day length i.e. time span between sunrise and simset and the total roosting hours of the egrets. Highly significant correlation existed for Cattle Egret r = .699 at P = 0.05, for Little egret r = .854 at p = 0.01, for Median egret r = .856 at P = 0.01
-..:^^^v and for Great Egret r = .866 at P = 0.01). Hence it can be concluded that as the day length increases the total roosting hours of the egrets decrease. Significant differences were also found between the pre- and post-roosting behaviours adapted by the four species. However, when the selection of roost site characteristics - ground cover, canopy closure, canopy level, tree height and girth at breast height, by the four species was compared no significant difference was found amongst them. Egrets for the most part of their life-cycles depend on wetlands, which are under tremendous pressure worldwide. Some possible measures to bring more heronries under state protection could be to ensure future availability of roosting and nesting sites vis- a- vis maintenance of large water bodies. For heronries there should be a security zone provided by water or dense undergrowth as barrier for predators. Area and quality of fresh water habitat, diversity of feeding patches, flight distances and ability to maintain periodicity in a species are important factors to sustain a viable population. The forest department should prevent ongoing poaching and protect breeding colonies during the nesting season. Reed removal and overexploitation of the open water for cultivation of water-chestnut may rob the egrets of potential feeding grounds. If unabated, fishing in the Lake and the Canal will also deplete the food availability to the egrets and cormorants. Paddy fields are important habitats of the egrets hence selective and harmless pesticides and fertilizers should be used in these fields. Water conservation should be given priority and alternative habitat should be made available so that in adverse conditions breeding and sustenance of the birds is not affected. Ensuring water during the summer season is also recommended so that food supply to breeding birds is not disrupted in the Lake. Local community provides traditional protection to the biodiversity at Sheikha Lake. This custom should be supported and encouraged when seen debilitating.
10 ECOLOGY AND BIOLOGY OF EGRETS WITH SPECIAL REFERENCE TO Egretta alba, E, intermedia, E. garzetta AND Bubulcus ibis IN AND AROUND ALIGARH
THESIS SUBMITTED FOR THE AWARD OF THE DEGREE OF Bottor of $I)tlo^optiP IN WILDLIFE SCIENCE
BY FAIZA ABBASI
DEPARTMENT OF WILDLIFE SCIENCES ALIGARH MUSLIM UNIVERSITY ALIGARH (INDIA) 2004 ?A
•:i T7165 bedicated to
My Great Grand Father
^fisan-uUdfi A SBasi DEPARTMENT OF WtLDLIFE SCIENCES ALIGARH MUSLIM UNIVERSITY, ALIGARH - 202 002 (INDIA)
CERTIFICATE
This is to certify that the thesis 'Ecology and Biology of Egrets with special reference to Egretta alba, E. intermedia, E. ganetta and Bubulcus ibis in and around Aligarh' is the original work of Ms Faiza Abbasi. The thesis submitted for the award of Ph.D. degree in Wildlife Sciences, Aligarh Muslim University, Aligarh is worthy of consideration for the award. She has thoroughly revised this thesis as suggested by the Indian examiner. I have gone through the revised thesis and I am fully satisfied with the revision. This work has been done by the candidate under my supervision.
JiUf Prof H.S.A. Yahya (Supervisor)
OF V^ -f DLIFE : CIENOBi A.K^.l.'.. ALiGABB -.^^
Countersignature ^ '^ "^ ii:>.
Tel. — Office . 0571 2701052 Telefax : 0671 - 2701206 m DEPARTMENT OF WILDLIFE SCIENCES ALIGARH MUSLIM UNIVERSITY, ALIGARH-202002 [INDIA]
^rof, H,S.A, Yahya PhD (Ornith) Chairman
J^ef..J\(o
CERTIFICATE
This is to certify that the thesis entitled 'Ecology and Biology of Egrets with special
reference to Egretta alba, E. intermedia, E. garzetta and Bubulcus ibis in and around
Aligarh' submitted for the award of Ph.D. degree in Wildlife Science of Aligarh Muslim
University, Aligarh, India^is the original work of Ms Faiza Abbasi. The work has been
done under my supervision.
(H. S. A. Yahya)
Tel —Office ; 0571-2701052 Telefax: 0571-2701205 Email : [email protected] Resi 0571-2706119 CONTENTS
ACKNOWLEDGEMENTS i LIST OF TABLES iii LIST OF FIGURES vi Chapter 1. INTRODUCTION 1.1 Introduction 1 1.2 Background 5 1.3 Hypothesis 9 1.4 Objectives and Rationale 9 1.5 General description of Ardeids 10
Chapter 2. STUDY AREA 2.1 Aligarh District 17 2.2 Sheiicha Lake 17 2.2.1 Historical background ' 2.2.2 Physical features 19 2.2.3. Climate 22 2.2.4 Flora and Fauna 24 2.2.5 Land use and conservation status 27
Chapter 3. SPATIAL PARTITIONING 3.1 Introduction 34 3.2 Methodology 38 3.3 Results 42 3.4 Discussion 48 Chapter 4. FOOD AND FORAGING 64 4.1 Introduction 69 4.2 Methodology 73 4.3 Results 76 4.4 Discussion
Chapter 5. TEMPORAL DISTRIBUTION 5.1 Introduction 93 5.2 Methodology 97 5.3 Results 100 5.4 Discussion 103
Chapter 6. ROOSTING BEHAVIOUR 6.1 Introduction 127 6.2 Methodology 130 6.3 Results 133 6.4 Discussion 135 SUMMARY AND RECOMMENDATIONS Future research directions 158 Conservation implications 159
References 163
Appendix I 190
Appendix II I93 Acknowledgements
At the onset, I am thankful to Prof. H S A Yahya, Chairman Department of WildUfe Sciences (DWS), Aligarh Mushm University (AMU), for supervising this work and bearing with me, which must have certainly been a test of patience for him.
I am grateful for the financial support I received by the administration of the AMU, for a period of three years.
Thanks are due to the faculty members of the DWS Drs. Jamal A. Khan, Afifullah Khan and Satish Kumar for their encouragement and also some fruitful discussions. I have learnt much that was required to accomplish this work from two former faculty members of DWS - Dr. A. R. Rahmani Former Chairman, DWS, presently Director of the Bombay Natural History Society, Mumbai and Dr. Salim Javed former Lecturer DWS currently Ornithologist, Environment Research and Wildlife Development Authority at the United Arab Emirates. I am deeply indebted to both of them.
I sincerely thank the people around Sheikha Lake, specially, the villagers of Sheikha village for their congeniality and hospitality during the field data collection.
The affable staff of the Library and Documentation Centre of the Wildlife Institute of India (WII), Dehradun has greatly obliged me while I conducted my literature survey there. I am deeply indebted to Dr. S. A. Hussain, Faculty member of the WII, for making it possible for me to navigate. I am also grateful to Mr. Rashid, Shaheen and Asghar, WII researchers and AMU old boys, for their unconditional help during my stay.
Thanks are due to Mr. Asim Zafar, Lecturer, Dept. of Computer Science, AMU for helping me in matters related to the computer and Mr. Mazharul Haque, Dept. Of Geography, AMU for helping me with the maps. I thank my senior research colleagues at DWS for giving me suggestions drawing form their own experiences in the friendliest manner. Specially Dr. Azra Musavi, Lecturer, Women's College, AMU for her friendly support, Drs. Ekwal Imam and Orus Ilyas, for their timely help and Mr. M. Hilaluddin, Tahmina Shafique, Drs. Shah Hussain and Ayesha Sultana for their kindness. Support from Mr. Junaid Nazeer Shah and Mr. Shahid Basheer Khan - my ex class mates, and my research companion, Sangeeta Singh was also valuable.
I am grateful for the cooperation of the non-teaching staff of the DWS - Mrs. Nasreen Hussain, Ex Seminar In-charge, Mr. Masroor Khan, Ex Accountant, Moonis Saleem, Ms. Anjum Ahmad and Mr. Ahmad Sayeed - the office bearers, Anees Zameer, Seminar In- charge, Chhote Khan, Abdul Ghaffar, Noor-us-Sayyam, Mohammad Omar, Ramgopal, Peer Mohammad and Yusuf - the attendants and Jaseem, Tanveer and Azeem - the Drivers.
It is beyond words to express my gratitude to Mr. Jamshed Siddiqui, my husband for his unparalleled help and cooperation at every step. Thankfully my children - Ahad Eiman alias Cherie (7) and Ebadat Eiman alias Sabrina (1) have been quite enduring of a mother preoccupied with a thesis. I owe a lot to my parents Dr. (Ms) Parveen Abbasi and Dr. Farhat Abbasi for their keen interest and encouragement in the progress of this work. Thanks are due to my sister Amna Abbasi for her help and uncle Mr. Ashraf Abbasi for his support. Finally, I extend gratitude to my cousin Tanya and aunt Ms Yasmeen for their constant support and encouragement.
^^ (Faiza Abbasi) List of Tables
Table 1.1 Comparative account of the measurements of various body 16 parts of the four sympatric species of egrets.
Table 3.1 Population of four sympatric species of egrets 53 and their comparative abundance.
Table 3.2 The percentage utilization of 15 microhabitats by four 54 sympatric species of egrets and their micro-habitat niche breadth.
Table 3.3 Habitat niche overlap (Morisita's measure of niche 55 overlap) amongst four sympatric species of egrets
Table 3.4 Aquatic habitat utilization pattern of four sympatric species 56 of egrets
Table 3.5 Percent terrestrial habitat utilization pattern of four 57 sympatric species of egrets
Table 3.6 Proximity matrix of four sympatric species of egrets with 58 other associated wetland avifauna
Table 4.1 Time devoted to different Foraging behaviours 83
Table 4.2 Food resource matrix of prey item for four species of 84 egrets
Table 4.3 Food resource matrix for prey size for four species of 85 egrets
Table 4.4 Levin's measure of niche breadth (B) and Hulbert's 86 standardized measure of niche (BA) diversity of behaviour and food resource for four species of egrets
Table 4.5 Horn's resource overlap (RQ) between four sympatric 87 species of egrets
Table 4.6 Overall resource overlaps in the independent condition of 88 resources (product of individual resource overlaps) for foraging behaviour, prey item and prey size for four species of egrets
Table 4.7 Overall resource overlaps in the dependent condition of 89
m resources (mean of individual resource overlaps) for foraging behaviour, prey item and prey size for four species of egrets
Table 5.1 General time and energy budgets of four sympatric species 110 of egrets
Table 5.2 Seasonal time and energy budgets of four sympatric 111 species of egrets Table 5.3 Daily time and energy budgets of four sympatric species of 112 egrets
Table 5.4 a Differences between general activity patterns of four 113 species of egrets
Table 5.4 b Differences in seasonal activity patterns among four 114 species of egrets
Table 5.4 c Differences in daily activity patterns amongst four species 115 of egrets
Table 5.5 a Time budget of the Cattle Egret over three different 116 seasons and times of the day
Table 5.5 b Time budget of the Little Egret over three different seasons 117 and times of the day
Table 5.5 c Time budget of the Median Egret over different seasons 118 and times of the day
Table 5.5 d Time budget of the Great Egret over three different seasons 119 and times of the day
Table 6.1 Mean sunrise time, emergence time from the roost, and 140 total time span for emergence in minutes of four sympatric species of egrets
Table 6.2 Mean sunset time, settling time and total time span for 141 settling in minutes for four sympatric species of egrets
Table 6.3 Monthly mean day lengths and total roosting hours spent 142 by four sympatric species of egrets
Table 6.4 Percentage of total number of individuals of a species 143 counted performing a particular pre or post - roosting
IV behaviour amongst sympatric egrets
Table 6.5 Mean of total number of individuals of the species sighted 144 selecting a class of Girth at Breast Height for roosting amongst four sympatric species of egrets
Table 6.6 Mean of total number of individuals of the species sighted 145 selecting a tree of a particular height class, for roosting amongst four sympatric species of egrets
Table 6.7 Mean of total number of individuals of the species sighted 146 selecting a tree with a particular class of canopy type for roosting amongst four sympatric species of egrets 147 Table 6.8 Mean of total number of individuals of the species sighted selecting a tree with a particular class of canopy closure for roosting amongst four sympatric species of egrets
Table 6.9 Ground vegetation cover at the roost site selected by four 148 sympatric species of egrets
Table 6.10 Roost counts of the four sympatric species of egrets 149
Table 6.11 Differentiation amongst four sympatric species of egrets 150 regarding roosting patterns
Table 6.12 Differentiation amongst four sympatric species of egrets - 151 regarding use of roosting behavior and resource characteristics offered by the roost site List of Figures
Figure 2.1 a Map of Aligarh District 29
Figure 2.1b Map of the intensive study area - Sheikha Lake 30
Figure 2.2a Max and Min temperatures in Aligarh in 2001 31
Figure 2.2b Average monthly rainfall in Aligarh in 2001 31
Figure 2.3a Max and Min temperatures in Aligarh in 2002 32
Figure 2.3b Average monthly rainfall in Aligarh in 2002 32
Figure 2.4a Max and Min temperatures in Aligarh in 2003 33
Figure 2.4b Average monthly rainfall in Aligarh in 2003 33
Figure 3.1 Mean of population for four sympatric species of egrets 60
Figure 3.2 Micro habitat use for four sympatric species of egrets 61
Figure 3.3 Dendrogram showing spatial associations of four sympatric species of 62 egrets with other species of the wetland
Figure 4.1 Percent utilization of various prey items by four sympatric species of 90 egrets
Figure 4.2 Percent utilization of various prey sizes by four sympatric species of 91 egrets
Figure 4.3 Percent utilization of various foraging behaviours by four sympatric 92 species of egrets
Figure 5.1a, Allocation of time to different general activities in the time budgeting 120 b, c & d pattern for four sympatric species of egrets
Figure 5.2a, Allocation of time to different general activities in the time budgeting 121 b, c «fe d pattern during the summer season of four sympatric species of egrets
Figure 5.3a, Allocation of time to different general activities in the time budgeting 122 b, c & d pattern during the monsoon season of four sympatric species of egrets
Figure 5.4a, Allocation of time to different general activities in the time budgeting 123 b, c & d pattern during the winter season of four sympatric species of egrets
VI Figure 5.5a, Allocation of time to different general activities in the time budgeting 124 b, c & d pattern in the morning period of four sympatric species of egrets
Figure 5.6a, Allocation of time to different general activities in the time budgeting 125 b, c&d pattern during forenoon and afternoon period of four sympatric species of egrets
Figure 5.7a, Allocation of time to different general activities in the time budgeting 126 b, c & d pattern during evening period of four sympatric species of egrets
Figure 6.1a Correlation between sunrise time and monthly mean emergence time 152 of Cattle Egrets
Figure 6.1b Correlation between sunrise time and monthly mean emergence time 152 of Little Egrets
Figure 6.1c Correlation between sunrise time and monthly mean emergence time 153 of Median Egrets
Figure 6.Id Correlation between sunrise time and monthly mean emergence time 153 of Great Egrets
Figure 6.2a Correlation between sunset time and monthly mean settling time of 154 Cattle Egrets
Figure 6.2b Correlation between sunset time and monthly mean settling time of 154 Little Egrets
Figure 6.2c Correlation between sunset time and monthly mean settling time of 155 Median Egrets
Figure 6.2d Correlation between sunset time and monthly mean settling time of 155 Great Egrets
Figure 6.3a Correlation between the monthly mean day length and total roosting 156 hours of Cattle Egrets
Figure 6.3b Conelation between the monthly mean day length and total roosting 156 hours of Little Egrets
Figure 6.3c Correlation between the monthly mean day length and total roosting 157 hours of Median Egrets
Figure 6.3d Correlation between the monthly mean day length and total roosting 157 hours of Great Egrets
vn CHAPTER 1
INTRODUCTION 1.1 Introduction
Egrets are large showy birds readily seen in most neighbourhoods and well appreciated by humans. They often nest on houses and in city parks and feed in pastures, meadows, flooded plains and along drains in towns. They also serve important ecosystem functions such as accelerating nutrient cycling at feeding grounds and regulating fish population (Kushlan 1976.
Miranda & Collazzo 1995). Our understanding of these functions is facilitated by information on the species' breeding biology, food habits and the extent of their dietary similarities (Kushlan
1978). In the west extensive information is readily available on these aspects (Jenni 1969.
Kushlan 1976, Custer & Osborn 1978, Hafner et al. 1982, Kent 1986b) but parallel data in the old world is scanty. Besides a general account of each species given by Ali & Ripley (1968). notes and museum specimen cataloging (Abdulali 1965, 1968) taxonomic discussions (Berlioz
1956) and miscellaneous observations (Ikeda 1956, Abdulali 1967, Bhargava et al. 1982, Jamdar
1984, Parasharya & Bhat 1987) few detailed Indian studies (Burg et al. 1994) are published on their feeding (Sodhi & Khera 1984 & 1986, Singh et al. 1988, Sodhi 1989) and breeding ecologies (Jha & Sarkar 2000, Hilaluddin et al. 2004). However, several survey reports on the extant and breeding sites of herons or water-birds (Naik 1987, Perennou & Santharam 1990.
Urfi 1993, 1997, Subramanya 1996) report on egrets alongside other species.
The Great Egret was the main symbol of concern for hunting bird for plumes in North
America and triggered the Audubon Movement. The same alarm regarding the Little Egret in the
UK was the reason for the establishment of the Royal Society for Protection of Birds in the nineteenth century. Yet the general conclusion is that most egret populations are not in danger of extinction and some to the contrary are expanding their populations and ranges (Curry-Lindahl
1978). For example, the arrival and spread of the Cattle Egret in the New world in the last
century presents an exceptional opportunity to see how an immigrant becomes established and
fits in with or takes over from indigenous species (Lowe-McConnell, 1967). In France too their
1 population has increased incessantly from a couple of breeding pairs (Hafner & Fasola
1997). Like other species, egrets too are a source of gene or natural designs to keep the future options in the biotechnology; a recreational or educational resource for the public in the burgeoning mechanized world. They are integral component of an ecosystem and have a definite role to play in nature. Egrets are friends of farmers as their excreta are good fertilizers. They congregate in ploughed agriculture fields and consume agriculture pests. At times they also flock around animal dumps at primitive slaughterhouses and carcasses processing centers to rescue man in disposing off animal carcass. They do not attack human or livestock. So there is direct link between the survival of them and that of the people (Bildstein 1997).
This study was undertaken to explore the ecology and biology of four sympatric species of egrets coexisting at Sheikha Lake, Aligarh, U.P., India and focuses on aspects of niche overlap, resource partitioning measures and mechanisms of ecological isolation adapted by the species to maintain coexistence.
One of the most central and fundamental questions that an ecologist can address is: why there are so many different kinds of plants and animals? The most basic qualities of a natural community are the kinds and numbers of species living in them. Hutchinson
(1959) suggested that the major determinant of diversity patterns would be the trophic interactions of organisms. This premise that consumer resource interactions and resource competition are the structures of a community (Tilman 1982) is the basis of the observations of this study. Answers to the hypothesis as to how organisms compete for resource and the way their competition promotes diversity have been providing clues to the mystery of nature. The concept of the resource-partitioning model assumes that the greater the differentiation in fundamental niches the lesser would be the intensity of competition (MacArthur 1972, Vandermeer 1972, Cody 1974, Whittaker and Levin 1975,
May 1981, Giller 1984). In case of Ardeids the question becomes more pertinent and intriguing because there are so many different species of herons with immense similarities in their morphology, ethology and ecology.
Stemming from the classical work of Gausse (1934) commimity ecologists have
long sought to understand how coexisting species utilize common resources such as food,
space or time. Lack (1971) suggested that two species of animals could coexist in the
same area only if they differ in ecology. He further illustrates that such ecological
isolation brought about through competitive exclusion is of basic importance in the origin
of new species, adaptive radiation, species diversity and composition of faunas. Earlier
Darwin (1859) drew attention to the importance of competition for resources, which are
not adequate for the survival of all the individuals bom because variety not monotony
normalizes the ecological communities as at each trophic level of the food chain there are
a restricted number of potentially competing species sharing the resources. Interspecific
competition may be stabilized intrinsically because two species are bound to differ to
some extent in exploitation. The actual details of resources, the methods of exploitation
or the degree of overlap do not matter provided that this simple maxim holds good
(Pontin 1982).
Theories on the natural regulation of species diversity in communities are aimed at refining the concept of the species niche (Schoener 1974). A species niche is defined as the position of a species in a community, for example its use of food resources, time of
activity, location, mode of interaction with other species and so forth. One of the early attempts to quantify the notion of species coexistence in terms of the niche was by Pianlia
(1972). He introduced an empirical index to measure the extent of similarity or overlap of the different species with regard to resource states such as selection of food size its availability and location of foraging.
Common association between the coexistence of competitors and niche differentiation has led many workers to seek evidence for competition simply by documenting niche differences between species in the field. As in case of five coexisting species of tits, Lack (1971) concluded that size of prey and hardness of the seed separates the species at most times of the year. This separation is associated with overall differences in body size and in the size and shape of the beaks.
It is difficult to choose from various explanations to ascertain exact mechanisms of ecological isolation, but in spite of all difficulties of making a direct connection between interspecific competition and niche differentiation there is no doubt that niche differentiation is the basis of coexistence of competitors. There are number of niche dimensions that work out differentiation. The first is differential resource utilization or resource partitioning which can be observed when species living in precisely the same habitat nevertheless exploit different resources. The second dimension is spatial and temporal separation based on resources utilized by ecologically similar species segregated along microhabitat differentiation or even differences in geographical distribution; and availability of resources to be utilized differing along time of the day or the season. The other major way in which niches are differentiated is on the basis of conditions. Two species may utilize exactly the same resources but if their ability to do so is influenced by environmental conditions and if they respond differently to these conditions then each nay be competitively superior in different environments.
1.2 Background
A short survey of the work done on isolating mechanisms in birds traces back to
Steere (1894), when he wrote 'no two species structurally adapted to the same conditions will occupy the same area. Grinnell (1904, 1943) was the first to state explicitly the principle of competitive exclusion as pointed out by Udvardy (1959). As illustrated by
Begon et al. (1990), the necessity for competitive exclusion was also contained in the mathematical equations of Lotka and Volterra (Lotka 1925, Volterra 1926) on the basis of which Gausse (1934) set up a model population in the laboratory to measure the changes in numbers of two species of microorganisms, which ate the same limited food supply. The concept that each species selects its habitat by psychological or recognition factors, which are not necessarily essential to its existence was hinted by Brock (1914).
Later it was found that Grinnell (1943) had also said the same and termed it competitive exclusion (Hilden 1965). The term ecological niche first used by Elton (1927) and
Grinnell (1917) is a kind of shorthand expression indicating the entire role played by a species in an ecosystem. In other words it can be termed as an abstractly inhabited hyper volume consisting of n number of dimensions, by a species in any ecosystem (Hutchinson
1957). But the intellectual atmosphere surrounding the concept of the niche was one in which the competitive exclusion principle was held as an important ecological rule
(Brewer 1988). Further it was almost universally believed at that time that the difference between closely related species are non adaptive and that they arise only at the level of the genus and higher (Robson and Richards 1936). Yahya (1987 and 2000) supported Huxley (1942) that big size differences between congeneric species of birds are a means of ecological isolation.
In natural communities species that occupy a similar ecological niche will compete with one another for resources that are limited in supply. This interspecific competition negatively affects fecundity, growth or survival of one or both species and its effects are considered to be density dependent (MacArthur 1958, Hutchinson 1959, May
1973, Rosenzweig 1981, Connell 1983 and Dudgeon et al. 1999). This theory of resource partitioning usually is based on the ability of a species to specialize along a critical resource dimension or environmental gradient (MacArthur and Levins 1967). Certain theoretical and experimental studies have concluded that niche differentiation, dissimilarity in activity pattern, foraging behaviour (food choice) or habitat use among competing species are necessary for competitive coexistence (MacArthur and Levins
1964, Schoener 1974, May 1973, Brown 1989). Competition between animal species has received much attention both from field as well as theoretical biologists. It is evident that competitive interactions between species play an important role in structuring communities (Cody 1974, Connell 1983, Tilman 1987 and Hairston 1989). It is considered to induce resource partitioning and can work as a selective force towards specialization of feeding processes (Gordon and lUius 1989). Three conditions are generally seen as a prerequisite for resource partitioning to occur (Weins 1989, De Boer and Prince 1990, Putman 1996): potentially competing species should have overlap in habitat use, share food and food availability should be limited. In the most extreme case competition leads to the exclusive use of a resource by one species making coexistence impossible (Schoener 1983, Belovsky 1984). Under these circumstances competition is no longer evident in the field although it may have had an important role in structuring the community in the past (Connell 1983, Putman 1996). However, stable equilibria can be found if each species exploits a resource not monopolized by others (Schoener 1983), which is frequently the case.
In India egrets are common species placed in the Schedule III of the Indian
Wildlife Protection Act (1972) amended in 1991. All the four species are doing quite well in the wild and moreover the cattle egret is even expanding its distribution successfully.
Under the new trend of research on wildlife where most of the studies are oriented towards endangered and threatened species the common birds are being forgotten. But in the history of conservation this may prove to be a mistake going by the fate of the imperial pigeon in Europe (Rahmani 2002) and now the vultures (Prakash 1999) and house sparrow (Vijayan 2003) in India and elsewhere. Data available on common birds when they are common can act as a baseline model for their future conservation if they ever face threats. Conservationists trying to solve the mysterious local extinction of vultures would not have groped in the dark for a while if vultures were properly studied when they were common.
Understanding regulation of relative abundance and species richness of communities has been and still is one of the most central topics of ecology (MacArthur
1972, Cody 1975, Diamond and Case 1986, Ricklefs and Schlutter 1993, Rosenzweig
1995). Several hypotheses have been presented to explain patterns of diversity (Nudds and Bowlby 1992, Rosenzweig 1995). Most of them include hypotheses about time, productivity, predation and competition (Hutchinson 1959, Connell and Orias 1964).
With time it has been realized that these hypotheses do not have to be mutually exclusive
7 because they can either interact or operate independently in time and space. Nevertheless over the past twenty years it has been a hotly debated subject (Simberloff 1983, Strong et al. 1984, Abrams 1986, Den Boer 1986). Despite a long list of studies there is still uncertainty as to what regulates competition and when and where it occurs (Nudds and
Bowlby 1992). One reason for this is the scarcity of experimental studies on resource limitation and of the factors affecting species co-occurrence and diversity (Morse 1974,
Reynolds 1978, Connell 1983, Schoener 1983 and Elmberg 1997).
Evolution is a mystery. We try to look for what happened in the past by what is happening in the present. Ever since Charles Darwin made his legendry voyage of H. M.
S. Beagle the secret behind the origin of new species has intrigued evolutionary biologists. To avoid competition animals get adapted to varying patterns of resource use behavior (Ricklefs 2000), and this gives rise to new species. The ensuing debate sharpens evolutionary thinking and perceptions about the fundamental issues related to variations in life histories (Moreau et al. 1944, Lack 1971, Skutch 1949) yet very few comprehensive studies have been devoted to solving this mystery within the vast spectrum of Indian avifauna barring Zacharias (1974), Vijayan (1975), Grubh (1979),
Yahya (1980), Vijayan (1984), and Datta (2001). Within the vast and interesting area of research on herons it would be worthwhile to take a step towards reconfirming the doctrine that the key to coexistence is resource partitioning.
Sheikha Lake is one such wetland where four species of egrets peacefully coexist.
Superficially they seem to be exploiting the same set of resources and two of them - the median egret and the little egret are also of the same size. In that case there has to be some factor that helped them evolve as two different species in the past and now stops the
8 one which is more fit fi-om eliminating the less fit. This work is an attempt to explore that
X factor in case of the four species of egrets, which have never before been studied in the present context.
1.3 Hypothesis
Drawing from the theories emerged out of earlier condescending upon the subject of speciation and niche separation the hypothesis to be tested on the basis of natural observations is that there is some niche separation between the four species of egrets found in the Sheikha Lake since they are sympatric and utilize exactly the same macro habitat. Various aspects of behavior, life history patterns and habitat use have been selected as a tool to approach the question and the study has been designed so as to propound whether or not the four species differ amongst themselves in these ecological and ethological traits as far as the use of resources and maintenance activities are concerned.
1.4 Objectives and Rationale
Considering the above hypothesis the focus of the present study is to quantify niche differentiation mechanisms amongst four sympatric species of egrets i.e. Cattle Egret
Bubulcus ibis. Little Egret Egretta garzetta. Intermediate Egret Egretta intermedia. Great white Egret Egretta alba, coexisting in Sheikha Lake, Aligarh, UP, India. The following objectives were set for testing above hypothesis:
1. To ascertain the status and populations of the four species of egrets within the
intensive study area.
2. To analyze the partitioning of resources in micro habitat use of sympatric egret
species 3. To depict their inter and intra-specific competitive spacing mechanisms.
4. To investigate their differences in food selection and use of foraging behaviour.
5. To quantify their various activity patterns - seasonal as well as diurnal.
6. To study the variations in roosting patterns and roost-site selection amongst egrets
With the above objectives in mind this research work was conceived and commenced in August 2000. After an initial survey of available literature, species and site intensive field study commenced from the beginning of year 2001 which came to an end in March 2004.
1.5 General description of Ardeids
There are 17 genera and 60 known species of Ardeids comprising Bitterns,
Herons and Egrets and 6 of them are threatened while one is extinct since 1600 (del Hoyo
1992). These Colonial nesting wading birds are one of the most conspicuous, popular and well-known components of wetland ecosystem (Hancock and Kushlan 1984).
References to these birds date from the Old Testament (Jeremiah 8:7) and they also appear routinely in ancient Egyptian art (Houlihan 1986). The name Egret comes from the French 'aigrette' meaning the plume feathers of the six species of white Egrets. These are a special breeding plumage only occurring through the breeding season. For many years they were popular in the fashion trade (Ali 1996). The term has since lost its original meaning and is now used to describe various members of the Heron family which neither have these plumes nor are they white.
Somewhat visually similar to Cranes, Storks and Ibises, they can be distinguished by long legs, necks, bills and large size ranging from 40 cm (Rufous-bellied Heron Ardeolu rufiventris) to 140+ cm (Goliath Heron Ardea goliath). They are short-tailed and hold
10 their long necks in an 'S' shape with the head held back between the shoulders even in flight. The neck is also an effective spear extending rapidly but only backwards and forwards. They are all carnivorous and most feed solitary in or near water using a variety of hunting techniques ranging from standing still to prey flushing. Some species nest and roost together in a certain tree or group of trees in heronries away from feeding areas and commute between the two. They have a wide range of display actions, which they use during courtship such as threat displays, upward stretches, bill snapping and rattling, circling and pursuit flights. Males will offer females twigs as gifts or as a hint that it is time to start building a nest. During the courtship period many species undergo colour changes to the soft parts of the body. Several species have different coloured morphs or forms.
A short description of the four species selected for this study follows in the forthcoming sections. Although several authors have suggested different nomenclatures for these species such as Ardea ibis, Ardea bubulcus and race Bubulcus ibis is some times treated as an allospecies (del Hoyo et al. 1992) for the cattle egret. Similarly for the Little
Egret and the Median or Smaller Egret Ardea garzetta and Ardea intermedia have also been used. Ardea alba is also used for the Great white Egret also called as Large Egret or
Great White Heron (Ali and Ripley 1968, Ripley 1982). The Median Egret is sometimes placed in monospecific genus Mesophoyx and alternatively Casmerodius as the Great white Egret is also more often placed in the genus Casmerodius than the Genus Ardea.
Work on DNA indicates closer genetic links with Ardea than Egretta for the Cattle,
Median and Great white Egrets (del Hoyo et al. 1992). However, for the ease of
11 understanding and convenience we have followed the widely known common and scientific nomenclature adapted by Hancock and Kushlan (1984). The following descriptions of individual species and particulars in Table 1.1 are mainly drawn from Ali and Ripley (1968),
Hancock and Kushlan (1984) and del Hoyo et al. (1992). The species accounts are also augmented with specific Indian studies.
1.5.1 Cattle Egret Bubulcus ibis coromandus Linneaus IDENTIFICATION: 50-56cm, 340 - 390 g. White egret with stubby aspect, short yellow bill and short dark green legs and pale yellow iris and lores. Hunched posture while at rest. Juveniles similar to non-breeding adults but may have a blackish or grey tinge. Sexes alike and attain long rufous-buff plumes on the crown, nape, lower fore neck and mantle during breeding season. Bare parts brighter during courtship. Non-breeding adults have duller bare parts and little or no buff plumage. Jamdar (1984) also reports a bird lacking white plumage. DISTRIBUTION: A native of the Old World and common from Africa east, south and east Asia, Australia and New Zealand. First new world occurrence reported in 1877 in British Guiana; current range expanded to a near cosmopolitan status (Snoddy 1969). HABITAT: Traditionally associated with ungulates. Least aquatic of all herons. Feeds in agricultural fields, suburban lawns, dense thickets, and shrubby vegetation near water and wetlands, reedbeds, marshes, mangroves, riverbanks, wet pastures and stream edges. Breeds up to 1500 m in India. Sedentary with far reaching dispersive movements in search of feeding grounds. FOOD AND FEEDfNG: Eats mainly insects, including lepidopterans and orthopterans, and small vertebrates, but also eats any other food they can glean. The young eat the same diet as the adults. Uses a variety of behaviours for prey-catching (Ikeda, 1956). It is diurnal and gregarious by nature. Loose flocks throng food abundant sites. BREEDING: Seasonal breeding peaks. Jun to Aug in North-India. Male territorial and aggressive; front forward threat displays, mutual preening during courtship and highly colonial nesting with other water birds on wet pastures open, marshy habitats and nesting trees 1 to 10 m high. Male collects nesting materials while female constructs nests of sticks, twigs, and reeds. 3-4 light bluish eggs in one clutch, normally incubated by both parents for 22 to 26 days. Semialtricial chicks with white down and nestling period is 30 days. Siblicide uncommon. STATUS: Not globally threatened. Abundant in India (Perrenou & Mundkur 1991). Schedule IV species of the Wildlife Protection Act (1972).
12 1.5.2 Little Egret Egretta garzetta garzetta Linnaeus IDENTIFICATION: 55 - 65 cm, 280 - 638 g. A medium sized polytypic heron, including dark grey morphs with white throat and intermediate morphs with mixture of white and grey. White form studied here is predominantly white with black bill and yellow feet. Sexes alike, juveniles as non-breeding adults, vary from having poorly developed ornamental plumes or no plumes. Breeding dress includes two or three lanceolate plumes from the nape, throat and slightly recurved ones of variable length at the back. DISTRIBUTION: Palearctic, from France, Spain and NW Africa east to Korea and Japan, scattered in Middle-east, India and southeast Asia. HABITAT: Wide variety frequenting all kinds of open wetlands, riverbanks, shallow lakes, pools, lagoons, irrigation canals, flooded meadows, rice-fields, marshes and inland dry areas. Coastal habitats such as mudflats, sandy beaches, coral reefs, mangrove covered shores. In India usually on muddy substrate, very scarcely on pure rocky or sandy shores. Normally in lowland but up to 1400 m in Nepal. Population mainly sedentary with some dispersal or nomadism. FOOD AND FEEDING: Variable feeding techniques depending on habitat and food. Feeds by walking, running, foot-stirring and open wing feeding. Also seen flying low over water to disturb and catch fish fishing in cooperation with merganser (Abdulali 1949, 1967). Defends food sites and opportunistically flips between solitary and gregarious feeding. Feeds even from the backs of partially submerged cattle or water-hyacinth (Parasharya & Bhatt 1987). May feed 7-13 Km away from colony in breeding season. Eats mainly fish but crustaceans, molluscs and insects and occasionally worms, reptiles and small birds too. BREEDING: Jul to Sep in North India. Nests colonially in large mixed colonies but individuals aggressively defend own sites. Male displays from a succession of temporarily established advertising territories. Forward displays, neck flicking, upright displays, grow calls and erection of plumes. Nest a small platform built by both sexes on ledges, reeds, trees and bushes below 20 m. Clutch size varies from 2, 3, 5 to 8 depending on race and so does the egg color from green-blue to off white. Both parents incubate eggs for 21 to 25 days. Chicks have white down, pink bills and feet later turning green. Fledgling 40 - 45 days. Breeding also reported from a heronry in the midst of an office compound (Naik 1990). STATUS: Not globally threatened. Schedule IV species of Wildlife Protection Act (1972) in India. Earlier farming was also done for plumes (Birch 1914, Anon. 1921, Benson 1922)
13 1.5.3 Intermediate Egret Egretta intermedia intermedia Wagler IDENTIFICATION: 56 - 72 cm, 400 g. An all white medium to large egret with stubby yellowish bill and dark legs. Sexes alike, juveniles look like adults except in breeding plumage distinctive, long aigrette back plumes extend beyond the tails. Fairly silent yet calls during displays. DISTRIBUTION: Discontinuous and patchy distribution in Africa, south and east Asia and Australia. Race intermedia breeds from Pakistan east through China and west Indonesia to Japan. HABITAT: Very varied, mainly inland habitats with abundant emergent aquatic vegetation including margins of fresh and salt lakes, ponds, banks of rivers and streams, rain ponds, swamps, flooded plains and dry grasslands and pastures with cattle close to water and less often in coastal mangroves, mudflats and estuaries. Inhabits lowlands but seen up to 1450 m in Nepal. Mainly sedentary with some nomadic movements. FOOD AND FEEDING: Solitary hunter using walking slowly, hovering and plunging and head tilting to prey upon mainly fish, frequently frogs insects and grasshoppers and even nestlings of herons. Aerial feeding observed in Keoladeo National Park, India with the little egrets (Sivasubramaniam 1988). Diurnal and solitary but sometimes in flocks of 15 - 20 (Sodhi & Khera 1986) BREEDING: Season varies regionally, Jul to Sep in North India. Aggressive during courtship performing upright, forward, flap flight, twig shake, snap, stretch and circle flights coupled with buzzing calls. Mutual preening, bill clapping and neck entwining takes place after pair formation. Breeding occurs in the rains or dry season always in large and mixed colonies on ledges, reedbeds or tall trees normally at height of 3 - 6 m but up to 20 m. The nest of reeds or twigs is completed by the female with material brought by the male. Lays 3-4 pale sea green and smooth yet slightly pitted eggs. Incubation period of 21 days in India, nestling 35 days, chicks with white down and fully fledged at five weeks. Also paired in captivity with Ardeola grayii (Parasharya 1985). STATUS: Not globally threatened. Schedule IV species of Wildlife Protecfion Act (1972) in India. Breeding colony may contain up to 1500 nests (Perrenou & Mundkur 1991).
1.5.4 Great White Egret Egretta alba Linnaeus IDENTIFICATION: 80-104 cm, 700 - 1500 g. Entirely white large egret with dark legs and feet, yellow to black bill, green lores and yellow iris. Characteristic S shape of neck, black line extends from the gape of the mouth to well behind the eye. Sexes alike, non-breeding adults have all yellow bill, dull greenish facial skin and lack ornamental plumes. Juveniles similar to non-breeding adults but yellow bill has black tip. Long back plumes develop during breeding season in addition to soft part colour changes. DISTRIBUTION: India, southeast Asia, Japan
14 and Korea South, through Indonesia to Australia and New Zealand. Extensive post breeding dispersal, tropical population sedentary. HABITAT: Generally a bird of wet habitats of all sorts (coastal and inland) occurring typically in marshes, damp meadows, swamps, river margins and lake shorelines, saltpans, mangroves and estuaries. Agricultural land specially rice-fields and drainage ditches are frequently used. Seldom also seen on dry pastures. FOOD AND FEEDING: Feeds both alone and in groups, mainly passive diurnal feeder. When feeding solitarily may vigorously defend its sites using erect posture, forward displays supplanted fights and actual attacks. Feeds gregariously when food is concentrated although with some conflict. Specializes in feeding by walking slowly and standing wading through shallow water and also on shore or dry land. Fish comprise the bulk of the diet, yet insects, amphibians and reptiles too are taken along wet margins. Small mammals can be important prey at dry ground and small birds also eaten occasionally. BREEDING: Plumes figure prominently in both antagonistic and pairing displays. Males defend display territories using upright, arched neck and forward displays, supplanting flights and attacks. May nest either solitarily or colonially in 10s or 100s of pairs. Nest in reed-beds, bushes and short trees over water at height of up to 50 m. Eggs are pale blue, incubation by both parents for about 25 - 26 days. Clutch size varies from 2 to 5, chicks have white down and white nestlings with yellow bills fledge after 6- 9 weeks of hatching. STATUS: Not globally threatened, Schedule IV species of Wildlife Protection Act (1972) in India.
Various aspects of the above mentioned four sympatric egrets have also been
subjects of comparison amongst themselves (Sodhi 1986 & 1992, Uthaman 1990) and with
other herons (Parasharya & Bhat 1984). Building upon section 1.3 & 1.4, the primary
question for this dissertation is detection and extent of niche partitioning mechanisms
amongst them as they coexist in the same ecosystem. This has been taken up with specific
background in the forthcoming chapters (3 to 6) for spatial organization, foraging patterns, temporal distribution and roosting activities in the same light.
15 44 o gj B o1 1 • 1 o o Q. u u ON
in Q. 00 E o fN >^ o C3 O o to oOJ
in OX) E rn 00 in u ON Q. c irj VO \D .2 O >. rn •oo in o
00 O o C •^^ a> 2i "« o bc o u aE ^ ^ (N >o u U (M ^ ON ON fa ii ^ O o (N r^ 00 M u IT) 00 00 OJ 'fc' ^O ^1 - -a OJ c a ^_^ < E o ^ c ^ c o b o ?o ^? ^e M (U i 1 CO tu C C/3 N ^ 03 I- (7;-3( C3 yo ^ s H m CHAPTER 2 STUDY AREA 2.1 Aligarh District Aligarh comprises the northern most part of the Agra division in the upper Ganga - Yamuna doab (the area between two rivers) region. It extends from 27° 29' N latitude to 28° 1 r N lattitude and 77° 29' E longitude to 78° 38' E longitude. To the north the boundary is purely conventional and touches the district of Bulandshahar; on the northeast the Ganges separates it from the district Badaun, on the east and southeast lies the district of Etah, on the southwest lies the district of Mathura, and on the west it is separated from Haryana by the river Yamuna. It is stretched over an area of 5000 sq km approximately and its length and breadth are 120 km and 72 km respectively. Aligarh is at a distance of 120 km from the National capital Delhi and well connected by road and rail network (Figure 2.1a). A survey of the district was done for egret populations and it was found that all four species of egrets under the scope of this study were found utilizing the Sheikha Lake round the year as a natural habitat. Considering its ecological compatibility, easy approachability and atmosphere conducive to fieldwork Sheikha Lake was selected as the intensive study area for this work. 2.2 Sheikha Lake Situated at a distance of 17 km from Aligarh the Sheikha Lake is a perennial lake spread over 250 hectares which is also home to a large number of waterfowls both migratory and resident. The Upper Ganga Canal (UGC) divides the area in two parts. For the convenience of the study we termed them as Sheikha 'A' and 'B'. However, the main lake is Shiekha 'A' on the western side of the canal. Sheikha 'B' becomes patchy in the dry season and segregates into several small pools. The metal road and the canal form 17 two of the boundaries of the lake while on other two sides it is surrounded by a tree line separating it from the agricultural fields (Figure 2.1b). 2.2.1 Historical Background The district of Aligarh has been an example of imperfect drainage of rain and floodwater since yore. Owing to these drainage defects there were several small and temporary marshes and lakes, which are mainly rainwater reservoirs confined to some natural depressions. Such wetlands were common around Sikandra Rao and Koil tehseels (administrative sub-divisions). There were fair sized lakes at Gopi, Ikri, Bhawan Garhi, Nagla Sheikha and Gursikaran and seasonal lakes such as Adhawan and Sengar. With the advent of the UGC in 1852 many of the drainage defects of the Aligarh district were rectified and hence the smaller marshes leveled up. The remaining wetlands were confined to the depressions in the higher levels of the country and through which the UGC passes. Details of the history and formation of Sheikha Lake are not found in any reliable government documents. For example only an occasional mention of a Jheel can be seen in some of the district gazetteers. However, survey of the region and inquiries from the locals suggest that prior to the construction of the (UGC) the area would have been a wasteland and converted into a marsh due to water logging from seepage of the canal. Further depression created by digging out mud for building the canal and accumulation of rainwater would have resulted in a Lake. Today it exists as a perennial wetland fed by rainwater as well as canal seepage. It is also speculated that several kilometer long belt of marsh had existed on both side of the canal but later reclaimed for agriculture under land reforms. Constant draining of water also affected these marshes and today they exist as 18 barren land. Only a few scattered patches of marshes have survived and Sheikha Lake is one of them. 2.2.2 Physical features 2.2.2.1 Location and approach Sheikha Lake falls between the latitude 27° 51' 21" North and longitude 78° 13' 05" East, in the upper Gangetic Plain of northern India. A part of the saline alkaline belt of western Uttar Pradesh, the Sheikha Lake lies in the southeastern region of the District in the Koil Tehseel of Dhanipur Block. It is located at a distance of 22 km from the Aligarh Muslim University campus on the Panaithi - Charra road that goes left from the Grand Trunk road towards Kanpur. The main villages in the vicinity of the lake are Bhavankheda, Changeri and Sheikha. The nearest small town with a bus station is Jalali, which is at a distance of 3 km from the Lake. 2.2.2.2 Topography The general surface of Aligarh district is a plain of remarkable fertility and the level is extremely regular. The configuration of the soil is characteristic to that of the doab and it slopes gently from north to southeast. The level rising sharply to the high sandy upland gradually descending inland to a depression drained by several rivulets. The Sheikha Lake lies in this central depression. Apart from a few sandy ridges alternated by shallow depressions, the land is uniform. The surface is varied by several depressions formed by the river valleys and natural drainage lines while the elevations consist merely of slight ridges of sand. The height of the ground surface where the UGC enters the district is 193.24 m above sea level and towards south the level drops to an ahitude of 160 m above sea level. 19 2.2.2.3 Soil The principal physiographic alluvial fillings and the major soil types of Aligarh district are influenced by the depositions of the two rivers Ganga and Yamuna. The main constituents of the alluvium are of clay, silts, sands and kankar (limestone conglomerate that results into a type of rocky earth) in several horizontal layers piled up in varying proportions and varying thickness. There are also a few tracts of infertile barren soil locally called usar. These tracts are filled with white slippery sand very fine in texture on which even grass refuses to grow. The local washer men use this soil for washing clothes and its vernacular name is reh. A type of inferior sand called bhur gives an arid appearance to some parts. The Sheikha Lake is a part of the fertile loamy belt formed by the low land khadar of the Kali river which gradually sinks into the broad central depression. Clay soil, imperfect natural drainage and numerous lakelets in which the surface water collects without finding an outlet characterize this tract. In consequence of the resultant saturation the tract is marred by frequent stretches of barren usar and the exudation of salt in the form of reh. 2.2.2.4 Rivers Any major river does not traverse the District, the Ganga merely touches it in the northeast while separating it from Bulandshahar and the Yamuna flows for a short distance along its western boundary separating it from the State of Haryana. The other streams running through the district are the Kali and the Isan (tributaries of the Ganga) the Nim (tributary of the Kali) and the Rind, Sengar, Karawan and Patawaha (tributaries of the Yamnua). However, by all means the most vital water body of the district and the 20 Sheikha Lake as is the UGC, which was commenced in 1842 and opened 12 years later (Atkinson 1875). 2.2.2.5 Ground Water Sand belts provide the main inlet for ground water. The depth of water from the ground level varies from place to place, ranging from 6 m to 9 m in the northern half of the district and 15 to 19 m in the southern half The water table near the Sheikha Lake is comparatively higher than the dry portions of the city and remains up to 19m. The general chemical composition of the water of the district is suitable for irrigation (Bahadur 1976). 2.2.2.6 Other wetlands There were broad tracts of lowland specially in tehseel Koil and Sikandara Rao. In this part of the district natural depressions were numerous but now there are no permanent big lakes. However, various water bodies of small or big sizes existed earlier. The major ones were at tehseel Koil in Gursikaran, Ikri and Adhawan, the last was the source of Sengar river. In Akrabad the large wetlands were at Ladhawa, Sahadi and Gopi. There was an extensive group of depressions in Sikandara Rao as well as a large complex of the broad lakes of Hasayan, Bakayan, Nagla Sheikha and Jao, besides several detached ponds at Bhisi and Jau. In the central depression of Khair also there were the large water- bodies named Ogar and Morehna. In addition to these there were several shallow depressions at Atrauli and a large lake at Dadon (Nevill 1909). Many of these lakelets have given way to siltation, draining and agricultural reclamation. 21 2.2.3. Climate The climate of Aligarh is typical of tropical monsoon type. Extreme variation in temperature and humidity are its characteristic features (Yahya et al. 1990). The region is characterized by three distinct seasons namely winter, summer and monsoon. Bright days, cold nights and low humidity are the features of winter season from mid November to mid March. Rains also occur for a short duration in January. Summer continues from mid March to mid June. May and June are the hottest months of the year. Hot and dusty wind called lou is prevalent in the region during summers. December and January are the coldest months of the year when the cold wave casts its spell for over a fortnight and the days are foggy with low temperature. This cycle of the major seasons is interspersed by spring season in March and the autumn break around October each year. Apart from monsoon during the rest of the parts of the years the sky remains generally clear or lightly clouded. However, for short spells of a day or two during the cold season the skies become cloudy and light showers may occur. 2.2.3.1 Temperature The region experiences extreme conditions of temperatures that rise to a maximum of 44° to 47°C during summers, and dips to even 0°C during winters. However, the average minimum temperature for winters ranges around 4°C to 5°C. There is an approximate difference of 10°C between the minimum and maximum temperatures of a day. More or less the same pattern was recorded by temperature rise and fall during the three years of study period (Figures 2.2a, 2.3a, 2.4a). Although the maximum temperature recorded in the study period was not more than 45° C even during extreme summers, the minimum temperature did drop to 0°C in the peek winters. This extreme 22 variation of temperature also accounts for the diversity of bird species in the region. The water temperature in the lake varies between 12°C and 30°C. 2.2.3.2 Rainfall Monsoon breaks usually during the first week of July and continues till the last week of August. Moderate rainfall, amounting to an aggregate of 644 mm annually is received during these months. However, the average annual rainfall received by the region on the whole amounts to 760 mm (Anon. 1976). About 87% of the annual rainfall is received during the south-west monsoon months from June to September, July and August being the two heaviest rainfall months. In the monsoon season the skies are generally heavily clouded and overcast on some days. The weather conditions and seasonal rhythms round the year make Sheikha Lake a pereimial wetland suitable to act as a waterfowl refuge during winters. A picture of the average monthly rainfall during the study period is given in Figures 2.2b, 2.3b and 2.4b. The pH varies form 7 to 7.8 and the content of dissolved oxygen fluctuates between 4.4 and 8.1 mg/litre at Sheikha Lake (Khan 1990) 2.2.3.3 Humidity Except during the southwest monsoon seasons (June to September) when the relative humidity is high - more that 85% usually - the air is generally dry over the district. The driest part of the year is during the summer season when relative humidity is less than 25% in the afternoon (Singh 1987). 2.2.3.4 Wind Winds in the District are generally light with a slight increase in summer and the early part of the monsoon season. During the period from October to April the Winds 23 blow mostly from north and west. South-easterlies appear in May. During the monsoon season winds are predominantly from the south-east and east. The mean wind speed is 5 km/hour (Singh 1987). 2.2.3.5. Special weather phenomena During the monsoon season the depressions originating in the Bay of Bengal, which move in a westerly or a northwesterly direction across the central part of the country, affect the weather of the District causing widespread heavy rains. During the cold season passing western disturbances affect the weather and a few showers occur. In the summer months the District often experiences dust storms. Thunderstorms also occur during the monsoon season some times accompanied with hail and squally showers. Fog occurs for a short period of two to three weeks during the cold wave with extreme cold conditions in winters. 2.2.4 Flora and Fauna Perennial water lodging, diverse weather conditions, shelter belt plantation and the adjoining canal favours a broad spectrum of living conditions for diverse life forms. The effect of the edges and ecotones phenomenon at Sheikha Lake supports rich avian diversity too. 2.2.4.1 Flora The terrestrial plant community around Sheikha Lake comes under the dry deciduous forest type as classified by Champion and Seth (1968). The most abundant tree species planted at the periphery of the lake are that of Terminalia arjuna and Schyzygium cumunii. Other trees with stunted growth are Accacia leucocephala, Accacia nilotica, Holoptelia integrifolia, Ficus religiosa, Dalbergia sissoo and Azadirachta indica.. At the 24 border of the Jheel there is thick growth of Prosopis juliflora. The major weeds are Lantana camara, Sida spp. Parthenium hysterophorus and Cassia tora. Plantations of Psidium gujava and Terminalia arjuna are present on one side of the jheel. The shrub species are Ipomea aquatica, Muraya koenigi and Lausonia enermis. The dominant grass species are Ischeatium sp., Saccharum spontaneum, Imperata cylindrica, Saccharum munja, Vetiveria zizanoides, Dichanthium annulatum and Setaria glauca. The submerged vegetation consists of Hydrilla, Ceratophyllum demersum, Vallisneria, spiralis, Potamogeton crispus and Naja spp. Free floating vegetation consists of Salvinia and Azolla sp. and in some places Eichhornia crassipes. Rooted floating vegetation includes Nymphoides cristata and Nymphoides indica (Saxena 1999). Details of the floral diversity are given in Appendix I. 2.2.4.2 Fauna Compared to a large variety of birds only a few mammalian species are found in this area. In addition to blue bulls Boselaphus tragocamellus and jackal Canis aureus, are Indian Mongoose Herpestes auropunctatus, Five-stripped Squirrel Funambulus pennanti. Porcupine Hystrix indica, Black-naped Hare Lepus nigricolis, and Rhesus Monkey Macaca mulatta are reported as identified with the help of Prater (1971). Several species of rats are also found. Amongst reptiles several species of snakes and fresh water turtles such as Lessymes punctata and the Geochlamys hamiltonii are found here. An occasional Monitor Lizard can also be seen in the terrestrial habitat. Sheikha is also rich in ichthyofauna and several species of amphibians also occur here. Insect diversity in Sheikha is also quite 25 abundant. Due to limitations of this study it was not possible to commence a comprehensive biodiversity assessment of the area. Avifauna - The main attraction of the Sheikha Lake are the waterfowl that inhabit the Lake in different combinations in different times of the year. A one square km perennial wetland surrounded on all four sides by thick plantations and a leading trail of forest on the adjacent canal banks is a sort of haven for the resident as well as migratory birds. They use the wetland for feeding and general activities, the adjoining crop fields supplement their feeding and the nearby thickets provide breeding and roosting sites. During drought years this wetland becomes more strategic for migrants and many waterfowl detour here even from Bharatpur a as pilot bird banding by Yhaya et al. (1990) has shown. Rahmani and Sharma (1997) have reported 161 species from Sheikha while in another study Yahya et al. (1990) described 188 species of birds from the environs of Aligarh. Though a threatened species the Sarus Crane Grus antigone are found in good numbers (largest flock of 28 seen during the study period). Black-necked Storks Ephippiorhynchus asiaticus and Black-headed ibis Threskiornis aethiopica - both near- threatened species (BirdLife International 2000) are found in some numbers. The lake is seen teaming with migratory waterfowl during the winters - Bar-headed Geese Anser indicus, the Grey lag Geese Anser anser, Ruddy shelduck Tadorna furruginea, Red- crested Pochard Netta ferina, Shoveller Anas clypeata and many others. Waders and herons also contribute to the waterfowl diversity of the lake. In addition to this it is home to many forest birds such as kites and eagles, doves and pigeons, warblers, cuckoos, parakeets and numerous passerines. 26 Although agriculture and livestock breeding is the main livelihood for the inhabitants around the Lake, it has never been subjected to unsustainable anthropocentric pressures for land or water. The area around the Lake is used for cattle grazing which is in the interest of the ecosystem health since it helps in pulling back ecological succession and maintaining the wetland in a serai stage, which would otherwise change into a climax terrestrial ecosystem. Apart from this a small amount of fishing, fuel wood and fodder extraction and utilization of the Sheikha 'B' pools for cultivation of water chestnut Trapa bispinosa is also done. Earlier the legal status of the Sheikha Lake was that of a Village Commons Land under the ownership of the Gram Samaj (village level local governing body). The Forest Department had done plantations around the Lake under the Social Forestry program a few years ago. At the time of the formation of the Upper Ganga Canal the Irrigation Department had also planted trees along the canal bank. Later these were also taken over by the Forest Department and now they exist as Protected Forests. The FD exercised its right of prohibiting hunting of the Scheduled species under the Indian Wildlife Protection Act 1972 ammended in 1991. Later Rahmani and Sharma (1996) suggested that it should be developed as a 'Multiple-Use Protected Area' with prohibitions on major habitat alterations, land acquisition and tree plantation. Presently Sheikha Lake is a Closed Area and a forest guard is to check poaching . 27 Sheikha Lake has got some conservation attention by authorities and scientists. It was first brought on the world ornithological and conservation map by Yahya et al. (1990) when a pilot project on bird ringing was initiated in the Lake and several waders with Russian rings and ducks ringed by BNHS elsewhere were recovered. Considering the support of the local community in the protection and upkeep of the Lake it was recommended to be included in the National Directory of Community Conserved Areas (Khan & Abbasi 2000). Recently it has been listed as an IB A site due to the large congregations of birds that it harbors. The Indian Bird Conservation Network (IBCN) at the Bombay Natural History Society (BNHS), Mumbai has listed it as an IBA (Important Bird Area) Site due to the large congregations of birds that it harbors (Abbasi and Yahya 2003, Islam and Rahmani 2004). It has also been listed as an important wetland of Uttar Pradesh by (SACON) 2004. 28 U] 125 oi 2 - Soi « son •» T '^a i •- ^ & 0.-= « « « a o B b o-f-o « w U « 0>£ 3 = O CO 0. 3 U S > I I 10 I I o Q. IS I 3 Figure 2.2 a: Max and Min temperatures and b: average monthly rainfall In Aligarh in 2001. 45 "ST 40 I 35 o Q. 10 I- 5 M M A O N D "Montn 250 200 I I 150 1 i 100 50 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months 31 Figure 2.3 a Max and Min Temperatures and, b: average monthly rainfall in Aligarh in 2002 45 40 (0 35 3 ID d> 30 O Ave. Max o 25 Ave. Min a> ^ 20 O o. lb F o 10 1- 5 0 -1 1 1 1 1 1 1 r n 1 1 JFMAMJJASOND Month 250 200 150 I •f 100 o: 50 M L Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month 32 Figure. 2.4 a: Max and Min Temperature and, b: average monthly rainfall in Aligarh in 2003. 45 4D ^35 _3 • 30 O O 0 25 -•—Ave.Max g'20 Q -«— Ave. I\^ E .• 10 —1 r- M M J J O N Months 250 200 I 150 I 100 50 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Source. Meteorological Station, Physics Department, AMU, Aligarh. 33 CHAPTER 3 SPATIAL PARTITIONING 3.1 Introduction There are often close linkages between the birds and the quality and structure of their habitat (Shankar-Raman 2003). Such is the influence of spatial distribution of resources over multi species assemblages that when resources are evenly distributed on a spatial scale there is little opportunity for one individual to command more than others. However, when they are patchily distributed some individuals may be able to defend better quality resources than others (Krebs & Davies 1981). Such influences also imply upon niche partitioning and natural selection. There is evidence that in an area where several species of geese are found breeding when the carrying capacity is reached the species compete for limited resources affecting their distribution in the area (Madsen 1985, Madsen & Mortensen 1987). Interspecific competition for food or foraging space has been implicated in various patterns of resource use in waterfowl (White & James 1978, Nudds 1983, Bustenes & Lonne 1997). Competition exerts its greatest effect on avian assemblages during periods of resource shortage (Baker & Baker 1973, Grant & Grant 1980), however biologists disagree as to whether resource limitation for waterfowl is highest during the breeding (Bethke 1991, Nudds & Bowlby 1992, Nudds & Wicket 1994) or non-breeding seasons (Dubowy 1988). Although the existence of competition is difficult to examine in highly mobile animals such as waterfowl, niche theory and Optimal Foraging Theory (OFT) provide testable hypothesis regarding resource use (niche breadth) and niche overlap between potentially competing species (Schoener 1986, Stephens and Krebs 1986). When food abundance is low species also may limit foraging to the microhabitats (patches) in which they forage most efficiently (MacArthur & Pianka 1966, Schoener 34 1982, Pulliam 1985). It is predicted that egrets would occupy a more limited set of micro- habitats as food abundance declines resulting in decreased breadth and overlap of the micro-habitat niche. As discussed in this chapter Egretta Spp. under the purview of this study provide a good opportunity for studying niche overlap because they interact in different combinations in different settings. They also show considerable dietary overlap (Chapter 4) and are broadly sympatric. But when they coexist to share a habitat they typically show vertical or horizontal segregation into different microhabitat types and often differ in body size (Cody 1985). Such consistent patterns of segregations have been interpreted as evidence for the importance of competition amongst egrets (Kent 1986b). Ardeid species have evolved to measure up to resource availability amongst conspecifics too. Egrets and herons even adjust the brood size relying on mortality to match the resources actually available. (Mock 1987, Mock et al. 1987, Mock & Lamey 1991). A variation in parental feeding behaviour corresponding to differential competitive abilities of the siblings, which is the behavioural cause of asymmetric growth and survival, and asynchronous hatching has also been reported in Little egrets (Inou 1985). Lack (1971) considered asynchronous hatching to be a mechanism that allows brood size to be reduced to the number that the parents can successfully raise, depending on food availability. Over time egrets like many other waterfowl have evolved to exploit the wide variety of niches available in the aquatic environment. A good example of such adaptive radiation exists in the geese of north America and Eurasia. The five species, which have traditionally wintered in Britain are adapted to feed in different kinds of habitat on the 35 areas of open land that existed before man felled the forest and introduced domestic grazing animals (Owen 1976). Studies of diversity patterns in north European waterfowls have found that species richness in assemblages of two sympatric dabbling ducks is associated positively with prey invertebrate abundance and habitat structural diversity (Elmberg et al. 1997). They have also shown remarkable results considering the assumed generality of food limitation that habitat structural diversity seems generally to be more important than abundance or diversity of food for species richness in dabbling ducks and other waterfowl guilds. Morphology is also used to index ecological relation relations in several studies of animal communities. Species of dabbling ducks have been found to segregate among habitat types according to size based prey profitability (Nudds et al. 1994, Poysa et al 1996). Another aspect of habitat selection in birds, which may be more important than food resources (Hoi & Winkler 1994) may be enemy free space (Jefferies & Lawton 1984). Temporal and spatial patterns in the activity and foraging to quantify differential niche partitioning and isolating mechanisms in heterogenous environments have also been taken up for mammals (Wauters et al. 2002) and amphibians (Wilbur 1982, Travis & Texler 1986). Spacing behaviour and interactions with other species have been studied for various aspects of an animals life history, mainly for the foraging and breeding functions (Dow 1979, Johnsingh et al. 1982). The study of avian niche relationships provides information about patterns of segregation among coexisting species that is a prerequisite to identifying the ecological mechanisms structuring avian communities (Hamilton 1958, 1962; James 1976, Rabenold 1978, Rice 1978, Sherry 1979, Sherry & Holmes 1988, Martin & Thebault 1996, Hudman & Chandler 2002). Although intraspecific effects may 36 explain patterns in communities composed of divergent species, they are invoked less frequently to explain coexistence among similar species. Potential mechanisms permitting coexistence of several similar species breeding in an ecosystem have been evaluated. Habitat characteristics, dimensions and positions of the performing individual and spacing patterns have been examined to evaluate possible models of species coexistence. In this study I have examined spatial partitioning based on niche theory and inter-specific effects as the primary mechanism structuring commimities (Hairston et al. 1960, Schoener 1982, Kelt et al. 1985, Bardsley & Beebee 1998, Beckerman 2000). If it is so then habitat use should be limited by interspecific competition. Under such conditions it is expected that habitat characteristics would differ among species. Alternatively intraspecific processes may also explain species coexistence. In this scenario habitat use by egrets should be limited by interactions with conspecifcs and we expected that selection of habitat parameters should be similar among species but vary within species. Positively associated spatial distributions of two sympatric and synoptic species of bee-eaters indicates that food competition is traded off by the species for improved breeding success in mixed colonies (Kossenko & Fry 1998). Competition influences life history features of a species not only due to the presence of sympatric species but also due to other non-related species exploiting the same habitat. Inter and intraspecific variations in the clutch size is also assumed to be a possible effect of competition with migrants (Katzner et al. 2003). Here in this study I have evaluated the variations in habitat exploitation by egrets as a possible effect of presence of migratory waterfowl in the Lake and classified them into clusters of occurrence. 37 Apparently four sympatric egret species seem to be utilizing the same habitat in Sheikha Lake, but based on the differences in the microhabitat selection it is assumed that there exists some form of niche separation -over the spatial scale between them so that they are allowed to co-exist. In the present study the habitat use and occurrence of egrets with their contemporaries in the Sheikha Lake have been undertaken to testify this hypothesis. The objective of this study was to quantify the ecological factors potentially influencing co-existence between the four sympatric species of egrets pertaining to habitat characteristics and species assemblages to determine if the egrets differentiated on a spatial scale. In this chapter I report on the population and comparative abundance of four species of egrets focusing on the non-breeding and non-roosting habitat exploitation in and around the Sheikha Lake. Secondly, I have documented the niche breadths of all the four egrets based on their selection of micro-habitat for survival. Extent of niche overlap between the four species corresponding to several habitat parameters has also been quantified. Thirdly, I have collected data on the associations of the egret species with conspecifics, congenerics, sympatrics and other major species that are also found utilizing the same habitat. 3.2 Methodology 3.2.1 Data Collection Three trails were identified in the study area. The first trail encircled the periphery of the Lake, the second trail traced the canal and its pools and the third one ran through anthropocentric settlements in close vicinity of the Lake and covered the village woodlots and crop fields utilized by egrets for foraging and roosting. Several micro-habitat types were identified such as Open water, Paddy field, Grass land. Lake shore, Reedbed, Canal 38 Bank and Ploughed field. Trails were laid down so as to cover all the possible habitat types in the study area. Throughout the study period these trails were monitored twice a week and for each sighting the numbers of individuals of an egret species seen on a particular substrate and utilizing the habitat were recorded. For all encounters the habitat type and specific habitat characteristics were noted. If the sighting occurred in aquatic habitat then water depth, water stretch in the Lake, aquatic vegetation type and cover were noted. When the sighting took place on a terrestrial habitat or a perch then ground cover, tree height and crown cover were noted. For all encounters distance from the closest human habitation was also recorded. If the sighting occurred within the Lake or within a human settlement then the distance was noted as zero. Estimation of vegetation cover on terrestrial as well as aquatic surface was done by the quadrate charting method following Mueller-Dumbois & EUenberg (199^) and Causten (1988) using a square meter frame. To assess the number of birds of the four species the direct count method was opted. Comparative abundance of the four sympatric species in different habitats was taken into consideration during analysis of data. Care was taken not to count the same individual repeatedly by monitoring the entire trails in a go and not back counting. Though the third trail ran through roost sites also, counts of number of species and species abundance taken on the roost site were not taken into consideration for spatial scale partitioning and population estimation as are discussed in Chapter 6. To be able to quantify species associations while analyzing the data I also measured distance of a foraging focal animal from the nearest conspecific or congeneric individual, nearest non-egret species and took ad libitum data of all other waterfowl 39 present in the wetland. When an individual foraged in at such a location that no other water bird, whether sympatric or not, was present within a distance of five-meter radius then the focal animal was considered as solitary. Whenever encounter was made with a flock the group size, flock composition and distance between individuals constituting a flock were noted. In case of such encounters distances from the nearest non-sympatric individual and presence of other species was also recorded. 3.2.2 Data analysis Population of each of the four species of egrets was derived by pooling the total number of individuals of a species counted in all observation of one monitoring. These daily figures were summed up at the end of the study period and mean was calculated. The outcome is considered as the approximate population of a particular species of egret. To assess the comparative abundance of each species error grams of the population size thus attained was made for the entire study period and population was assessed by calculating the 95% confidence limits (Fowler & Cohen 1986). Comparisons were made with the student independent sample t-test for significant differences between respective abundance of the four species. A comparison was made of the frequency with which a species used a particular micro-habitat type or the different habitat parameters available with x^ for k independent samples. Chi-square contingency analysis (Seigel 1956, Fowler and Cohen 1986) was done to test the significance of associations between a species of egret and a micro- habitat type and different habitat parameters such as water depth, vegetation cover, ground cover, stretch of water, tree height, canopy and distance from the Lake. 40 The computations of niche relationships were done by the computer programme NICHE (Krebs 1989). Estimation of the micro-habitat niche breadth for all the four species was done by using the Shannon-Weiner Measure (Colwell and Fuentes 1975, Krebs 1989). Given the resource matrix the formula is: //' = Ipy lOgPy Where H' = Shaimon-Weiner measure of niche breadth Pj = proportion of individuals found in or using a resource/ (j = 1,2,3, , n) n = total number of resource states The Morisita's index of similarity (Morisita 1959) was used to quantify the degree of overlap in the habitat utilization pattern of the four species of egrets. It was calculated from the formula 2Zp,y logp ik C= — S" p „ [(n „ - 1) (Nj -1)] +1" p ,i [(n ik -1) (N, -1)] Where C = Morista's index of niche overlap betweeny and k species. p ij = Proportion resource / is of the total resource used byy species p /i = Proportion resource / is of the total resource used by k species n, y = Number of individuals of speciesy that use resource category /. n,J: = Number of individuals of species k that use resource category /. Nj N ^ = Total number of individuals in sample (S n ; y = NJ; L n , ;t = Nk) Spatial associations of the egrets amongst themselves - with conspecific, congeneric and sympatric individuals, and with the other waterfowl utilizing the same habitat are analyzed by the cluster analysis and expressed in a dendrogram produced by 41 the single linkage-nearest neighbor method. The cluster analysis is a classification technique for placing similar entities or objects into groups or clusters arranged in a hierarchical tree like structure called a dendrogram. The sampling unit taken in this study is the Lake considered as one quadrate and the Q-mode presence-absence distance matrix of different members of the waterfowl community in the Lake was subjected to Cluster Analysis performed using the computer program SPSS. 3.3 Results 3.3.1 Population The population estimates of four species of egrets show that the cattle egret was present in largest numbers followed in decreasing order by the median egret, great egret and the little egret. (Table 3.1, Figure 3.1). Analysis of comparative abundance of the four sympatric species of egrets reveals that highly significant differences exist in the population sizes of CE-LE at t = 37.4, P<0.05, CE-ME t = 3.04, P<0.05, CE-GE t = 99.3, P<0.05, LE-ME t = 87.8, P<0.05, ME-GE t = 79.1, P<0.05and LE-GE at t = 17.9, P<0.05 level of significance. 3.3.2 Habitat utilization For ascertaining the spatial partitioning between four sympatric species of egrets on the basis of habitat utilization pattern nine different micro-habitat types in the terrestrial as well as aquatic ecosystems were identified (Table 3.2, Figure 3.2). Chi- sqaure contingency analysis of the frequency with which each species used these micro- habitat types reveals that highly significant associations exists between the species and the habitat types. The cattle egret used a variety of habitat types both aquatic and terrestrial but preferred freshly upturned soil of the ploughed crop fields and dry 42 grassland amongst terrestrial habitat types while amongst the aquatic types it preferred reedbeds with low height vegetation growth and irrigated paddy fields {x =213.6, P<0.05, df = 288). The little egret (x ^ = 232.7, P<0.05, df = 288) mostly remained in open sheets of water within the lake and at the shore. Amongst its less preferred ventures into the terrestrial area it remained in short grasslands. The median egret however, (x = 256.8, P<0.05, df = 288) showed high preference for reedbeds {x^ 139.1, P<0.05, df = 288).and made equal use of paddy fields, lake shore and marshes. The Great egret (x ^ ^^ 297.3, P<0.05, df = 288) seems to be specializing in open water feeding making use of the clear sheet of water within the lake and other pools. Three-habitat parameters vis. water depth, emergent vegetation cover, and stretch of water in the wetland were selected in the aquatic ecosystem of the study area (Table 3.4). Analysis of utilization pattern of these habitat characters under various categories reveals that significant associations exist between the four species and different categories of water depth. The cattle egret prefers to remain in shallow reaches (x = 234.2, P<0.05, df = 288) when feeding in water and treads over vegetation, while the little egret (x ^ = 477.8, P<0.05, df = 288) and the median egret (x ^ = 285.4, P<0.05, df = 288) mostly stay in water up to 30 cm deep. Owing to itls longest legs the Great Egret (X - 274.3, P<0.05, df = 288) is the only species of the four, which ventures up to 70 cm deep waters. The aquatic vegetation cover was also differentially selected by the four species for foraging. While the cattle (x ^ = 184.5, P<0.05, df = 288) and the median egret (x ^ = 109.6, P<0.05, df = 288) fed in highly vegetated areas, the little egret (x^ =119.2, 43 P<0.05, df = 288) and the large egret (x^ = 122.4, P<0.05, df = 288) fed in scantily vegetated areas. Out of the several categories of available water stretch in the wetland there was differential association of the four species with various categories. The Cattle egret (x^ = 248.6, P<0.05, df = 288) frequented the wetland when the stretch of water was less than 50% while for the little egret (x^ ^ 194.7, P<0.05, df = 288) the preferred stretch of water in the wetland was more than 25%. The median egret (x^ =233.1, P<0.05, df = 288) frequented the Lake when the stretch was upto 15% and the great egret iX^ = 242.9, P<0.05, df = 288) fed in the Lake when the stretch was more than 50% and even when the Lake was over flowing due to heavy rains. Four-habitat parameters vis. tree height, canopy cover, ground cover and distance from the Lake were identified in the terrestrial ecosystem of the study area to determine the habitat utilization pattern of four sympatric species of egrets (Table 3.5). Occurrence data of egret individuals in the various categories of tree height put to analysis does not suggest significant association between the species and tree height. Similarly for categories of canopy closure also non-significant associations were produced between species and canopy closures. However, highly significant associations were found between the terrestrial habitat characteristics of ground cover and distance of the individual from the Lake. The cattle egret (x^ = 274.3, P<0.05, df = 288) frequented ground vegetation cover only where h was more than 30%, whereas the little egret (x^ = 146.2, P<0.05, df = 288) frequented areas with less than 30% ground vegetation. The median egret did not exhibit significant association with ground cover but the great egret (x^ "= 203.5, P<0.05, df = 44 288) showed significant preference for ground vegetation cover up to 60%. Significant associations were also found with the species and their distance to the Lake. While the cattle egret (x ^ = 266.4, P<0.05, df = 288) was mostly found feeding away from the lake. The little egret (x^ -313.5, P<0.05, df = 288) maintained strict proximity to the Lake area. The median egret (x^ = 186.7, P<0.05, df = 288) did venture away from the Lake but remained within a distance of one kilometer. The great egret (x =302.8, P<0.05, df = 288) was one species found to feeding only in the close vicinity of the lake and its adjoining pools and never beyond one-kilometer distance. Analysis of the niche breadth (Table 3.2) shows that the cattle and the median egrets use a wide spectrum of habitat types hence they have a larger niche breadth. While the great egret has a lesser diversity of habitat types and smaller niche breadth followed by the little egret. According to the Shannon-Weinner's measure, the cattle egret has the largest niche breadth the median egret stands second to it as they exhibit a greater diversity of micro-habitat type utilization pattern. Degree of niche overlap between the four sympatric species of egrets regarding various parameters of habitat type (Table 3.3) indicates that the maximum overlap exists between the Little Egret and the Great Egret. The Cattle Egret has near negligible overlap with any of the species for all habitat parameters - in fact zero overlap exists between Cattle Egret and other three species in case of vegetation cover. The Median Egret shows moderate overlap with Little Egret and Great Egret adapting a somewhat similar fashion for both the contemporaries. However, niche overlap inference about two of the terrestrial habitat parameters i.e. tree height and canopy cover cannot be drawn here because in the 45 preceding step of deriving Morisita's index of niche overlap the Chi-square contingency analysis has revealed a non-significant association between the species and these habitat parameters. 3.3.3 Species associations The cluster diagram (Figure 3.4) depicts the classification of the wetland species based on their similarities in abundance pattern. It shows the single linkage tree diagram (nearest neighbor method) based on the Euclidean distances. As no objective criteria exists to use the value of Euclidean distances as the separating groupings, I considered mid-point of the Euclidean distance as the separating point and groups were separated by midpoint value of cluster interpretation. The clusters revealed in the dendrogram suggest that the four sympatric species of egrets have specific associations with the other species of the waterfowl community in the Sheikha Lake when the entire wetland is considered as one guild. The two major clusters were found - A and B. A consists of the four species of egrets and the other resident waterfowl starting fi-om the red-wattled lapwing to the woolly-necked stork. The second cluster B mainly consists of the winter visitors from bareheaded goose to the gull billed tern, except the last three occurrences - large cormorant, pied kingfisher and whit-tailed lapwing, which have low densities. Not withstanding the selection of a particular foraging distance from these species (which is treated in another data matrix. Figure 3.5) it may be inferred here that the frequency of visits of the egrets to the wetland for the purpose of foraging is impacted by the presence of other species. While the egrets frequent the wetland almost always in the presence of resident species the occupation of the space of the Lake and the sustenance activities of 46 the migratory waterfowl within the Lake causes deterrence of the egrets on a spatial scale. Based on the demarcations between the abundance of these species on the Euclidean scale the dendrogram has been divided into seven clusters. The Cattle egret is placed in the first cluster with the most common five species present in the Lake on all occasions. The next cluster of 11 species generally utilizing the Lake consists of the rest three species of egrets under the purview of this study. The third cluster has 13 species that are lower in abundance but a regular feature of the Lake. The fourth and the cluster of segment 'A' is that of three resident birds seen seldom in the Lake. However, the seventh and the last cluster of the 'B' segment also consists of those three resident birds which are rarely seen in the wetland. The 'B' segment has three clusters out of which the last one is of resident birds. The clusters five and six of this segment are of those water birds that visit the wetland only during the winter season. The fifth cluster comprising of 13 migratory waterfowl is high in abundance, whereas the sixth cluster of four species is low on an abundance hierarchical scale. The interpretations from the proximity matrix depict that the little egret is closest to the median egret (30.00) amongst sympatric species and to the white-breasted kingfisher and the pond heron (36.00) amongst non-sympatric species with respect to frequency of utilization of the Lake. The Median egret has a reverse relationship with the little egret but its proximity to non-sympatric individuals differs with the latter as it is closest to red-wattled lapwing (23.00), pond heron (22.00) and Black Drongo (27.00). The Great Egret and the cattle egret are the proximate species amongst the sympatric 47 group for each other at (31.00) and for the Great Egret the closest non-sympatric species are the black-winged stilt and the red-wattled lapwing at 21.00 and the pond heron at 26.00. For the Cattle Egret in terms of sharing the wetland on number of occasions the nearest non-sympatric species is the white-breasted-kingfisher at 27.00. This pattern suggests a negative association of the egrets with some species and a positive association with others. 3.4 Discussion Dynamics within an included niche have been discussed since Hutchinson's (1957) classical paper defining the niche as an N-dimensional hypervolume. Included niche dynamics have been inferred from a number of different studies on wide ranging taxa (Miller 1964, 1967, 1968, Jaeger 1970a & b, Morse 1970, 1974; Cameron 1971, Colwell & Fuentes 1975, Rusterholtz 1981a and b, Joem and Klucas 1983, Gilbert 1985, Bennett 1990). In systems where broad generalists coexist with more specialized species included niche dynamics are common (Colwell & Futuyama 1971). The results of the study indicate that there is niche partitioning on the scale of spatial heterogeneity amongst the four sympatric species of egrets because they compete for limited sets of resources and here the limiting factor is the space. Based on the locations of the foraging individuals it was observed that the Cattle, Little, Median and Great egrets occupied sites with similar tree heights and canopy covers. Nevertheless, there were detectable differences in the composition of the ground space utilized by the four species in terms of cover and distance form the Lake. On the other hand in the aquatic habitat there is partitioning between the species for all habitat parameters. 48 These generalizations lead to an expectation that four species of egrets coexisting at Sheikha Lake might occupy slightly different micro-habitat within their overlapping niches. Some species may be suffering due to this and hence making adaptations to meet the energy requirements by enhancing the foraging time selecting other food patches or items. Unlike the cattle egrets the other three species remain extremely wary and dare not enter areas close to human habitations. Thus segregation involves little egret and large egret restricting to fishing in the open waters and the median egret also making use of reeds and shores. While, the cattle egrets in an attempt to avoid competition select terrestrial habitats with high insect diversity and unsuitable for the other three species. Furthermore, the Little and the Great egrets differ in selection of prey item and prey size while feeding on the same micro-habitat (Chapter 4). In many communities species similar along one or more niche dimensions are dissimilar along others (Cody 1968 and Schoener 1986). Such niche complimentarity has been demonstrated earlier too (Amat 1984, Dubowy 1988, Bustnes & Lonne 1997). A look at the comparative abundance of the four species indicates that species with highest niche diversity index also exist in the ecosystem in larger numbers. This is in conformity with the general observation that diversity in habitat is an important factor contributing to the maintenance of an abundant and diverse population of herons. The results are consistent with other published work on niche separation patterns of sympatric species. Similar inter- and intra-specific space use patterns have been observed in allopatric and sympatric species. Fasola et al. (2002) have found strong competition, habitat heterogeneity, bad previous outcome and temporal variation of the habitat to be promoting the phenomenon of dispersal in Little Egrets, depending on their relationship 49 with the physical and biological factors. Erwin (1975) has tested Snowy and Great egrets to the assumptions of the optimal foraging theory in patch use of a given space and found difference in their patterns of patch use. Habitat use differences among snowy egrets, tricolored herons and little blue herons in Florida Bay (Recher & Recher 1968) and Tampa Bay (Kent 1986b) have been derived with considerable overlap. Hafner et al. (1986) have observed temporal variations in habitat quality promoting the Little egrets at the Camargue, (Southern France) shifting between habitats provided by natural and artificial lakes and adjacent rice-fields. Similar patterns have been observed in herons by Seigfried (1971), Quinney & Smith (1980), Reeders (1983) and Moser (1984). Given the lack of interspecific territoriality and aggression, studies on bird assemblages suggest that they should exhibit some other pattern of spatial segregation (James 1976). Darwin's finches have showed pronounced morphological adaptations over the long-term to different feeding substrates (Tebbich et al. 2004). Squirrels have exhibited preference to different tree species and positioning variable activity centres on spatial scales (Wauters et al. 2002). Unusual spatial organizations correlated with body size and food preferences has also been observed in other species (Dow 1979). Co-occurrence data on spatial niche segregation pattern between the four sympatric species of egrets pertaining to the results of this study suggest that they differentiate between the other species exploiting the wetland by having different proximity levels to different species. Adjustments in habitat utilization pattern of the egrets have been observed to vary depending on the presence of other waterfowl. All four species have been found to reduce the frequency of their visits to the Lake in the winter 50 season when competition for food and space in the wetland becomes severe due to the arrival of the migratory birds. This pattern is also supported by various other studies in the past (Sale 1974, Schoener 1982, Wilbur 1987 Bowers & Dooley 1991, Rhode 1991). Negative association is affected by differences in habitat selection, behavioural exclusion or repulsion and effect of past population histories (Pielou 1972). A vision of the spatial affinity and habitat similarities of egrets within themselves and with other species indicated that resources in terms of space available for foraging are abundant for those species having a high overlap. And, therefore, they spatially distribute each other in such a way resulting in negative association. However, co-occurrence of egrets differing in body confirms that distribution over an eco-morphological guild of the egrets allows co-occurrence without food and space competition. If the present results are extrapolated to generality in nature something else besides interspecific competition - heterospecific attraction affecting species assemblages or a factor related to resource limitation, must be the process regulating co-occurrence in egret assemblages. Finally, this study cannot be regarded as proof that interspecific competition for space does or does not determine species co-existence because resource limitation was not demonstrated. Nevertheless studies on interspecific association among birds in India are few (Vijayan 1975, Yahya 1980, Johnsingh et al 1982, Vijayan 1984 and Rahmani &, Manakadan 1987) and more research is needed. Our observations and experiments in this study highlight the extent of spatial niche partitioning between superficially similar micro-habitats and give some indication of the mechanism underlying this segregation. Where overlap has been observed in most aspects of spatial use absence of niche partitioning and exclusion has been observed 51 amongst the four sympatric species. No evidence of intense competition within the adult individuals was observed (Miniscule chasing interactions observed during the period of this study. See Chapter 5). Our observation of the egrets is rather contradictory to the other species where agonistic spacing interactions are observed due to interspecific conflict related to predation, roosting site and food resources. Passerines are generally reported to be chasing those coexisting species which compete for the same set of food resources in a foraging space and allow to trespass urmiolested those species that exploited different food resources (Morse 1970, Gaston 1977, Johnsingh et al. 1982). Most studies on congeneric birds have pointed to ecological differences that diminish competition in respect of their having different ranges, habitats and food (Perrins & Birkhead 1983). Niche partition and interspecific competition is not easy to define: a generally accepted definition is an interaction between species that results in reduced densities of both (Pontin 1982). Ecological differences in egrets are minimal and seem to be less in sympatry particularly where they live and breed in mixed colonies. In the light of most of the world's egret population increasing within this century (Meyerricks 1962, Recher & Recher 1969, Hafner 1997), interspecific competition for space should be looked for in future studies. This may affect local distribution of the involved species and ultimately it may become a factor in limiting population growth. 52 o m o o o o o o o o o o o o o o o o -t—» (U IT) O VO vo C O ON in m (U m 00 ON -^ o (D > OS ON 4-> ON oo ^ TO O) U C o ^ fD •o o s u (^ t—1 r<-i o o r^ o m O C in r<-) u-i 'o r-1 »—1 (n JD m m 03 m O i_ Z •* nS (30 Q. r^ :^ r- r-> t- 1:^ E — ^ (N -^ (N ^ o s § « u O) ON ON _> t~- in O r-- in NO NO o a> U r-i (N rn O T3 ^ CZ5 -H -H JJ C -H -H -H O S 4^ .—1 -H "o TH *Proportion of individuals Habitat Type Cattle Little Median Great Egret Egret Egret Egret Marsh 6 14 9 10 Ploughed field 27 4 8 0 Pool 0 6 0 23 Open water 0 31 11 42 Paddy field 7 13 12 7 Dry Grassland 34 7 12 0 Lakeshore 0 22 8 18 Reedbed 21 36 0 Canal Bank 5 3 4 0 Shannon-Weiner's niche breadth H' 325.05 301.96 313.29 305.48 (Determined by recording where each individual was first sighted. The percent values are of 110616 total encounters made in the 3456 collective sightings of all species during the entire study period). 54 4^ «> -i^ in >n O ^ •* 00 00 1-H o ON ' 1 0^0 O'^N 2 g o ^^ r-- .S£ o Q ii •*- u « •B o in • PM fl L. 00 O Q. .£ s S (N (N © >• O u J«3 fc. O 55 O U • PH b. CL >^ E 4> ci- . 00 >- U o ^ in U c ** in in 1_ a> O o o H £ a •4-1 cn c ON o o o J3 (N 00 E O O O O CL jU i_ > 0* S o c •oM o o o (N ON y -w o o o 5 L. o o o (N (N ON 'c V a tt) > o o o o O o V4— CL I 00 in in o o (N o o oCi OJ O) u ro c -• < o in m (N o o o O O o -Q 'a) o o X to M W w O O O I I a W w I- U C/3 o u Table 3.4: Aquatic habitat utilization pattern of four sympatric species of egrets at Slieil Sp ecies Habitat Characteristic CattUe Egret Little Egret Median Egret Great Egret WATER DEPTH (cm) 0-10 86.6 2.1 37.4 00.5 10-20 11.1 35.9 32.9 20.2 20-30 2.3 39.7 23.1 23.8 30-70 0 13.4 0 32.5 70-80 0 6.2 0 09.6 80-100 0 1.6 05.4 08.1 >100 0 1.1 01.2 05.3 WATER STRETCH >10% 41.8 02.2 27.6 01 10-25% 30.5 12.4 18.5 5.7 25 - 50 % 17.2 17.6 21.3 12.3 50 - 75 % 07.1 32.3 15.1 40.8 75-100% 03.4 30.8 14.4 22.4 >100% 0 04.7 03.1 17.8 VEGETATION COVER 0-20 % 0 65.9 9.6 78.3 20 - 40 % 0 22.1 10.4 19.1 40 - 60 % 13.6 06.7 33.2 2.6 60 - 80 % 14.5 04.4 28.7 0 80-100% 71.9 0.9 18.1 0 (Percent of number of individuals counted utilizing a particular habitat characteristic) 56 Table 3.5: Terrestrial habitat utilization pattern of four sympatric species of egrets at Sheikha Lake (2001 - 2004) Species Habitat Characteristic Cattle Egret Little Egret Median Egret Great Egret TREE HEIGHT (m) 0-5 10.8 13.9 22.1 21.4 5-10 14.6 15.1 11.8 22.3 10-15 17.3 22.4 15.5 16.7 15-20 21.9 12.5 16.3 14 20-30 18.4 19.3 19.2 13.1 >30 17 16.8 15.1 12.5 CANOPY 0-10 28.1 22.2 24.5 29.1 10-30 21.4 20.9 23.7 29.5 30-60 24.7 26.3 25.2 21.8 60-100 25.8 30.6 26.6 19.6 GROUND COVER (%) 0-30 12.4 90.8 29.5 73.2 30-60 38.7 9.2 31.3 26.8 60-100 48.9 0 39.2 0 DISTANCE FROM LAKE (m) 0 3.9 71.3 39.2 59.3 0-500 6.8 14.6 30.4 23.6 500-1000 9.2 7.4 9.8 13.4 1000-1500 30.2 5.1 12.2 3.2 >1500 49.9 1.6 8.4 0.5 (Percent of number of individuals counted utilizing a particular category of habitat characteristic) 57 Table 3.6: Proximity matrix of four sympatric species of egrets with otiier associated wetland avifauna based on Hierarcliical Cluster Analysis of their presence for habitat utilization in the Sheikha Lake (2001 - 2004) Egret species Associated wetland species Little Egret Median Egret Great Egret Cattle Egret Little Egret .000 30.000 52.000 35.000 Median Egret 30.000 .000 42.000 33.000 Great Egret 52.000 42.000 .000 31.000 Cattle Egret 35.000 33.000 31.000 .000 Little cormorant 53.000 51.000 59.000 34.000 Large Cormorant 228.000 236.000 226.000 241.000 Grey lag goose 126.000 132.000 146.000 137.000 Bar headed goose 161.000 163.000 171.000 176.000 Lesser whistling duck 170.000 184.000 198.000 189.000 Ruddy Shelduck 152.000 160.000 150.000 155.000 Comb duck 125.000 129.000 137.000 136.000 Cotton Pygmy Goose 74.000 68.000 66.000 53.000 Gad wall 119.000 125.000 133.000 134.000 Mallard 231.000 245.000 249.000 250.000 Spot-billed duck 87.000 85.000 73.000 68.000 Northern Shoveller 114.000 118.000 124.000 115.000 Pintail 126.000 134.000 130.000 129.000 Common Pochard 125.000 139.000 139.000 136.000 Tufted duck 170.000 192.000 198.000 195.000 Eurasian Wigeon 125.000 131.000 131.000 128.000 White-breasted Kingfisher 36.000 30.000 38.000 27.000 Pied kingfisher 177.000 183.000 171.000 186.000 House swift 55.000 41.000 33.000 32.000 58 Sams crane 62.000 52.000 36.000 41.000 White-breasted Waterhen 65.000 43.000 43.000 46.000 Purple moorhen 61.000 39.000 39.000 42.000 Indian moorhen 78.000 56.000 48.000 51.000 Common coot 107.000 113.000 117.000 108.000 Redshank 72.000 66.000 64.000 57.000 Sandpiper 60.000 44.000 42.000 37.000 Ruff 72.000 70.000 62.000 65.000 Black winged stih 41.000 29.000 21.000 18.000 Pheasant tailed jacana 73.000 65.000 69.000 54.000 Red-wattled lapwing 37.000 23.000 21.000 18.000 White-tailed lapwing 190.000 196.000 178.000 189.000 Gull-billed tern 213.000 225.000 227.000 224.000 River tern 174.000 184.000 192.000 189.000 Marsh harrier 56.000 56.000 66.000 53.000 Little grebe 133.000 141.000 155.000 146.000 Indian Darter 74.000 58.000 74.000 57.000 Pond heron 36.000 22.000 26.000 17.000 Grey heron 59.000 59.000 69.000 52.000 Purple heron 67.000 61.000 69.000 52.000 Glossy ibis 106.000 104.000 76.000 87.000 Black-headed ibis 68.000 52.000 64.000 55.000 Spoon bill 115.000 121.000 129.000 126.000 Painted stork 74.000 60.000 58.000 51.000 Open-bill stork 73.000 57.000 63.000 54.000 Woolly-neck stork 114.000 100.000 102.000 103.000 Black-necked stork 101.000 85.000 97.000 98.000 Black drongo 41.000 27.000 31.000 22.000 Bronze Winged Jacana 68.000 56.000 54.000 59.000 59 Figure 3.1: Mean of population of four sympatric species of egrets based on total counts of restricted areas in and around Sheikha Lake (2001 - 2004) 300 200- 100- lU GO O S -100 SPECIES jT] Cattle Egret {2} Little Egret 3j Median Egret 4J Great Egret (Results obtained from 304128 total encounters made in the 3456 collective sightings of all species during the entire study period). Figure 3.2: Proportion of individuals of four sympatric species of egrets found utilizing different micro-habitat types at Sheikha Lake (2001 - 2004) 120 100 Ice |LE c \ME m IGE %. ^o MICRO-HABITAT (Determined by recording where each individual was first sighted. The percent values are of 110616 total encounters made in the 3456 collective sightings of all species during the entire study period). Cattle Egret (CE), Little Egret (LE), Median Egret (ME), Great Egret(GE) Figure 3.3: E)endfX)gram based on habitat utiKzation showing spatial associations of four sympatric species of egrets with the other species of Sheikha Lake (2001 - 2004). ******HIBRARCHICAL CLUSTER ANALYSIS*** Dendrogram using Average Linkage {Nearest Neighbor) Rescaled Distance Cluster Combine CASE 0 5 10 1» 20 25 . + + + +- + Label Num +- R W LAPWING 34 POND HERON 41 BLAK DRONGO 51 B W STILT 32 CATTLE EGRET 4 W B KINGFISHER 21 HOUSE SWIFT 23 LARGE EGRET 3 SANDPIPER 30 LITTLE EGRET 1 MEDIAN EGRET 2 SARUS CRANE 24 LITTLE CORMORANT 5 PURPLE MOORHEN 26 COMMON MOORHEN 27 W B WATERHEN 25 0 B STORK 48 B H IBIS 45 REDSHANK 29 PAINTED STORK 47 GREY HERON 42 PURPLE HERON 43 C P GOOSE 12 MARSH HARRIER 38 P T JACANA 33 62 DARTER 40 RUFF 31 B W JACANA 52 SPTBLD DUCK 15 GLOSSY IBIS 44 B N STORK 50 W N STORK 49 B H GOOSE 8 L W TEAL 9 RIVER TERN 37 TUFTED DUCK 19 COOT 28 SPOON BILL 46 G L GOOSE 7 GADWALL 13 LITTLE GREBE 39 SHOVELLER 16 WIGEON 20 J POCHARD 18 PINTAIL 17 RUDDY SHELD 10 COMB DUCK 11 MALLARD 14 GULLBIL TERN 36 LARGE CRMRNT 6 PIED KNGFSH 22 W T LAPWING 35 (See Appendix II for abbreviated common and scientific names of waterfowl species in the dendrogram) 63 CHAPTER 4 FOOD AND FORAGING 4.1 Introduction Foraging seems to be the strongest relationship between a species and its habitat since competition for food is not only responsible for the movements of a species but also regulates populations and influences individual reproductive success. Documenting diet composition and dietary responses to environmental variation yields important knowledge about patterns of resource use. Because food is an essential resource researchers have often hypothesized that food niche differentiation is an active target of natural selection (Smith 1995). Partitioning may occur through independent selection of resources or may be determined by active interspecific competition. In many instances however, food may not be a limiting factor and resource use may be opportunistic, with all species tending to exploit the most profitable habitats and locally abundant prey types (Fasola 1994). Documenting inter-specific variation in diet composition among coexisting species may help identify whether species use the food resources in an area opportunistically or selectively. Combined with data on use of foraging habitat (Chapter 3) such information also helps to determine the probable range of species' responses to changing environmental conditions. This knowledge in turn enables development of ecosystem management strategies that accommodate various management actions and sustain ranges of prey and predator species. Since important ecosystem functions such as accelerating nutrient cycling at feeding grounds and regulating fish population (Kushlan 1976, Miranda & Collazzo 1997) are served by egrets, our understanding of these functions is facilitated by information on the species' food habits and the extent of their dietary similarities (Kushlan 1978). Probably this is the reason why breeding and foraging behaviours 64 occupy the largest share of research on formulation of conservation strategy and developing an understanding of the ecology of egrets (Schoener 1971, Krebs & Cowie 1976, Pyke et al. 1977, Krebs 1978, Krebs et al. 1981) At the same time competition for food also plays an important role in sibling aggression and breeding success (Mock et al. 1987). A majority of them are on prey catching and foraging behaviour of Egrets and Herons (Kushlan 1976, Hafner et al. 1982, Hancock & Kushlan 1984, Draulans 1987). Lotem et al. (1991) found differential strike success of foraging little Egrets in different depths of water. Hafner et al. (1986) have explored the role of foraging success in breeding little Egrets. Krebs (1974a) demonstrated a positive correlation between flock size and rate of food intake in the Great Blue Heron. A similar result was obtained for the Little Egret (Hafner et al. 1982, Cezilly et al. 1990). Scott (1984) has revealed that cattle Egrets exhibit a higher foraging efficiency when they feed in groups near cattle herds and that there is a potential cost associated with feeding too near others unless the prey are relatively small and abundant. Metz et al. (1991) have studied the effect of feeding with con-specifics on the foraging efficiency of Cattle Egrets and Thompson et al. (1982) have found their associations with the grazing cattle as per the predictions of the optimal foraging theory. Campos & Lekuona (1997) have observed temporal variations in the feeding strategies of herons owing to breeding activity. Feeding behaviour also provides useful indications for socio-biological processes amongst Egrets. Mixed species foraging behaviour and competition and overlap in food has been studied in many other species of birds too. Within mixed species flocks each species has a unique foraging niche (Seigfried 1976, McKnight & Hepp 1998, Warkentin & Morton 2000; Chen & Hseih 2002) and important differences exist in life histories between 65 species even within a homogenous group (Yahya 1980, Warham 1990, 1996). Extensive differences size, morphology, diet and foraging behaviour have been discovered among albatrosses (Permycuick 1982, Weimerskirch 1998, Cherel & Klages 1998, Weimerskirch & Guionnet 1998). Rolando et al. (1997) have found contrasts in the feeding time, rate and foraging techniques of the coexisting chough and alpine chough. Haley and Gjerhshaug (1997) have made similar revelations for sympatric eagles. Benvenuti et al. (2001) have found foraging behaviour in razorbills adjusting to the marine environment during daily cycles. Cruz (1980) detected food resource overlap amongst four associated species of north-American vireos. Four sympatric species of Darwin's finches have been found using food, feeding substrate and feeding techniques differentially by Tebbich et al. (2004). Behavioural plasticity based on dominance relationships for food competition also contributes to niche partitioning within sexes (Pasinelli 2000). Overlap in food amongst herons has been studied by various authors for several species but probably not with reference to the Cattle, Little, Intermediate and Great Egrets. Erwin et al. (1985) have observed differences in feeding activity and success of Little Egrets in different habitats reflecting differences in prey density and availability in the relevant habitats. Lowe - McConnel (1967) found that there is little overlap amongst the aquatic feeding indigenous herons (Snowy Egrets, Little Blue Herons and Tricolor Herons) nesting together since their feeding behavior is very different. Evidence exists that similar size herons partition resources among themselves. Erwin (1975) has tested assumptions of the Optimal Foraging Theory on foraging Great Egrets and Snowy Egrets and found the two species using different techniques. Snowy Egrets fed with greater efficiency and intensity during the breeding season and left patches when their capture 66 rates declined and spent more time foraging in patches when other birds were present. Great Egrets on the contrary showed few of these tendencies, although they did leave patches when their inter-capture intervals increased. Satiation differences having some influence over their feeding rates. Jenni (1969) found differences in food items, behavior and foraging depth among four herons in freshwater in Florida. Willard (1977) while working in fresh and salt-water marshes in New Jersey found that larger herons ate larger fish and fed in deeper water than did smaller herons. Whereas medium sized herons ate similar sized fish but used different habitats and behaviors. Rodgers (1983) in a study on herons foraging behaviour in Tampa Bay suggested similar sized herons foraged in a similar manner. Several studies have considered foraging as a partitioning mechanism among coexisting heron species. Whitfield and Blabber (1979) found that segregation was achieved through a combination of prey size and wading depth among four different sized herons in Lake St. Lucia, Natal, south Africa. Custer and Osborn (1978) found that Great Egrets fed in deeper water than did the smaller Snowy Egret Egretta thula. Homs (1983) found differences in prey size among snowy Egrets, Great Egrets and Great Blue Herons Ardea herodias in a California salt marsh. Aggression may disrupt normal foraging behaviour causing sub-ordinate species to reallocate time that otherwise would be devoted to foraging within the habitat. Aggression could operate more subtly by forcing subordinate species to avoid aggressive species thereby lessening opportunities to obtain prey. The resuh should be differential success rates with dominant species having a greater rate of energy intake than subordinate species. Alternatively what is best for one species may not be best for 67 another species. Morphological or physiological differences between species could result in different requirements or in different prey catching abilities (Pulliam & Caraco 1984, Grant & Grant 1980). Under such conditions each species should have a different set of optimal resources. Natural selection could produce differences in habitat or prey selection and energy intake should be comparable (Kent 1986b). Habitat and prey differences are the typical means of resource partitioning among herons (Jenni 1969, Willard 1977, Custer & Osborn 1978, Whitfield & Blaber 1979). Among various heron species many foraging patterns have been observed (Meyerriecks 1962, Recher and Recher 1969, Kushlan 1978, Hancock & Kushlan 1984). A foraging Egret experiences a conflict of interests between allocation of attention to prey and to predators or other danger. Predation amongst foraging Egrets is a goal- oriented behaviour under which two basic postures are recognized each of which corresponds to a particular attentiveness inferred from the birds' visual field (Hancock and Kushlan 1984). In the upright posture the bird detects prey in a large area of water and is able to scan for predators. In the crouched posture the effect of refraction is decreased (Katzir 1985) leading to a greater precision of capture movements, but scanning for predators is considerably reduced. Studies in psychophysiology have shown that the initial arousal of attention on perceiving a target (before any capture attempt is made) is necessary for the correct choice and ordering of subsequent processing operations (Beaubaton 1985). This chapter considers how sympatric Egrets chart their foraging routines, foraging behavior and selection of food for coexistence in a single habitat. Species that are able to coexist and exploit similar foods must have developed adaptations of structure 68 or function. In the present study it has been attempted to compare the foraging behavior, extent of feeding and food of four species of Egrets coexisting in a freshwater perennial wetland the Sheikha Lake. A literature survey revealed that a study on this aspect and with similar objectives has not been done in the past. My objective of the study was to determine the extent of resource overlap and identify potential mechanisms by which partitioning is maintained with regards to the foraging ecology of these four species. 4.2 Methodolgy 4.2.1 Data collection I observed foraging Egrets at Sheikha Lake from August 2000 to March 2004 (excluding the summers of 2002). As practiced by Yahya (1980) I divided 12 hours of daytime into three shifts of four hours each. The morning shift began at 0600 hrs and ended at 1000 hrs. The after noon shift began immediately after ranging from 1000 hrs to 1400 hrs. the last shift was that of the afternoon from 1400 hrs to 1800 hrs. Observations were carried out for at least one shift each day and I tried to allocate equal observation time to each of the shifts so that daily rhythms could be covered. Although general activity pattern of the species was studied usually the foraging behaviour was given special emphasis. Formatted records on foraging behavior, ecology and food of four species of Egrets were taken based on their availability. The average observation distance was maintained around 10 meters and the help of 8 x 20 binoculars and a spot scope was taken for observing foraging individuals belonging to one of the species. Total time spent in foraging was calculated from the general activity records. Foraging behavior - The species under the focus are flexible in their use of resources and employ a variety of foraging behaviors. Following Hancock and Kushlan 69 (1984) ten behavioural phenomena used by foraging Egrets covering all four species under the focus of the present study were identified - Walking slowly, Standing, Foot stirring, Chasing, Probing & Pecking, Walking Quickly, Hopping, and Gleaning. Focal Animal Sampling following (Altman 1973) was done to study the foraging behavior. I restricted these behavioural categories to body movements, foot movements and aerial methods only and did not distinguish between postures, wing movements and head and neck movements such as neck swaying or wing flapping. The duration of time spent by the bird in pursuing these behaviors for foraging was recorded. Each species was given equal observation time in a particular shift to avoid bias. I also tried as far as possible to cover as many individuals by constantly changing the focal animal based on their availability in the field. The total observation time devoted to all species was 1622 hours and the break-up for each species is as follows: CE (24197 mins), GE (24321 mins), ME (24422) and LE (24379); in the entire study period. Food - Since Egrets feed on a wide variety of prey item (Hancock and Kushlan 1984) handling time for most of which is not more than two seconds (Recher & Recher 1968, Krebs 1974a, Bayer 1985) and during this time the bird is often moving shaking its head and/or holding prey crosswise in its bill and the prey can be squirming or violently flexing it was not possible to identify the prey up to species level. Hence prey item was identified to the lowest possible taxon. The observations were recorded under ten taxa - aquatic insects, terrestrial insects, crustaceans, molluscs, amphibians, small fish, fish, repfiles, small birds (nestlings) and small mammals (Rodents). The number of jabs or pecks made by an individual as a feeding attempt were counted and if a prey item was 70 seen in the bill it was considered as successful and the category of the prey item was noted. As in Bayer (1985) prey-size was estimated as a proportion of bill length (Recher and Recher 1969, Seigfried 1971a, Krebs 1974a, Willard 1977, Kushlan 1978, Caldwell 1979, Quinney & Smith 1980, Homs 1983, Kent 1986b & Mock et al. 1987, Forbes 1989). Figures from AH and Ripley (1968) were taken and an average was reached upon for male and female bill lengths and divided in fractions of quarters, fifths or thirds. Prey were observed in categories of 2 cm up to larger than 10 cm. Prey smaller than 2 cm size was not recorded. Some of the error in this method could be cancelled when many prey were caught in each bill-length class. Tendencies to over and underestimate could also be compensated by practicing accuracy in appraising classes of prey length with the help of dummy prey and marked bill placed at field observer distance. Prey sizes corresponding to bill length classes for Cattle egret were 2-4 cm for one third bill length, 4-6 cm for two third bill length, 6-8 cm for larger than bill length and 8-10 cm for double bill length. In case of the Little egret and Median Egret they were 2-4 cm for one fourth bill length, 4-6 cm for half bill length, 6-8 for three fourth bill length, 8-10 cm for full bill length and >10 cm for larger than bill length. For the Great Egret this proportion was reached upon by dividing the bill in five parts 2-4 cm for one fifth bill length, 4-6 cm for two fifth bill length, 6-8 cm for three fifth bill length, 8-10 cm for four fifth bill length, >10 cm for full bill length. However, it was not possible to measure the standard error of prey size thus estimated due to the inability to calculate mean of observations recorded in classes or categories of a particular range. 4.2.2 Data Analysis A comparison was made of the frequency with which each species used a foraging behaviour, food item and prey size with x ^ for 'k' independent samples. Chi- square contingency analysis was used to test the significance of associations between a 71 species and a behavior, prey item and prey size (Seigel 1956) following Fowler & Cohen (1986). The Chi-square statistic was calculated by the following formula: (0-E)- X^ s E Where, O = Observed frequency E = expected frequency which is the sum of the expected frequencies of each cell in the contingency table calculated by multiplying the sum of the row with the sum of the column and dividing it with the grand total. The degree of freedom is (r - 1) x (c - 1) Food item and prey size in the categories of food and foraging behaviours in the categories of behaviour were considered as one resource type each and resources matrices for all species were structured following Pianka (1986). Levins (1968) diversity index was used to estimate the extent of behaviour and resource use. 1 Levins' Diversity Index B 2 SPj Which can also be written as Y B = SNj 2 Where, B = Levins' measure of niche breadth 72 Pj= fraction of items in the diet that are of food category j/proportion of individuals found using resource state j or behaviour] (estimated by Nj/Y) (IPj = 1.0) Nj = Number of individuals found in or using resource state or behaviour] Y = E Nj = Total number of individuals sampled Niche breadth was converted to Hulbert's standardized measure B-1 BA= - -- B varies from 1 to n where n is the number of categories. There are a number of measures to quantify niche overlap however, they all generally give the same resuhs, Horn (1966) index was used to determine the degree of overlap between species since in conditions other than where resource use can be expressed in number of species, it is recommended to be the best measure of overlap (Krebs 1989). S (P'i + Pik) log (p,j + Pik) - S pij log pij - I pik log Pik Ro = 2 log 2 where RQ = Horns' Index for overlap for species j and k Pik = Proportion resource / behaviour I is of the total resource utilized by species k py = Proportion resource / behaviour I is of the total resource utilized by species k All the calculations were done using the computer simulations in the program NICHE modified from Krebs (1989) in a Fortran based program. 73 4.3 Results For the study of differential use of foraging behavior amongst four sympatric species of Egrets eight behaviors types were selected (Table 4.1). Chi-square contingency analysis of the frequency with which each species made use of these behaviors suggests that associations between the species and the behaviour types are highly significant. Cattle Egrets used a variety of feeding behaviours with walking slowly, standing and walking quickly most often (X ^ = 32.7, P<0.05, df = 21) and Little Egrets used walking quickly and foot stirring most often. (X ^ = 33.4, P<0.05, df = 21). The behaviour of foot stirring was unique to the Little Egrets. The Median Egrets used walking slowly most often but gleaning, probing and pecking and standing were also used with an equal thrust iX^ = 37.9, P<0.05, df = 21). The Great White Egret almost specialized in using the walking slowly and standing behaviour (x^ = 34.3, P<0.05, df = 21) with miniscule use of probing and pecking and chasing. The percentage utilization of 11 prey items by four species of Egrets at Sheikha Lake was recorded by counting the number of prey items belonging to various taxa captured by the individual while its activities were observed by Focal Animal Sampling. Table 4.2 is based on a total number of 7826 sightings. Goodness of fit tests reveal that there exists a significant association between species and favourite prey item. Cattle Egrets preyed upon terrestrial insects and small vertebrates such as amphibians, molluscs and crustaceans most often (x^ = 44.5, P<0.05, df = 30), the Little Egret was most associated with small fish but equally included crustaceans, amphibians and aquatic 74 insects {x^ =48.9, P<0.05, df = 30), the Median Egret most often fed upon small fish but larger fish and aquatic insects too formed a considerable portion of the diet, {x^ ^ 46.2, P<0.05, df = 30), where as the Great Egret almost exclusively fed upon fish - the larger ones constituting more than one half of the diet (X ^ = 43.8, P<0.05, df = 30). The rest of the dietary items were also consumed by the GE but in smaller quantity. Prey type analysis based on size shows a significant association between the size of prey eaten and species of Egrets. Cattle Egrets subsisted on smaller prey of less than 6 cm (X ^ = 22.8, P<0.05, df = 12), prey eaten by little Egret ranged from 2 cm to 8 cm {X^ =11\, P<0.05, df = 12); similarly the median Egret too preyed upon intermediate size fish and crustaceans less than 8 cm in size (x = 25.2, P<0.05, df = 12) but the Great Egret maximized on fish larger than 8 cm (;^ ^ = 24.7, P<0.05, df = 12). However, since they eat small fish too some of their prey was less than 6 cm. The measurement of niche breadth (Table 4.4) indicates that Cattle and Median Egrets use almost the same diversity of foraging behaviors and the Little Egrets and Great Egrets use a very small variety of behaviours - practically only walking quickly and foot stirring; and walking slowly and standing. The Cattle and Little Egrets showed equal diversity in choice of food items and the Median and Great Egret show a little less diversity than the former two. Regarding prey size little egret showed a very high diversity followed by median egret and the great egret and cattle egret exhibited a comparatively lower diversity. 75 Analysis of resource overlap amongst four sympatric egrets (Table 4.5) reveals high overlap between CE and GE regarding behaviour, moderate overlap with prey type but very little overlap in prey size. GE and ME showed high overlap in foraging behaviour and considerable overlap in prey size and prey type. ME and LE exhibited almost total overlap in prey type but little overlap in foraging behaviour. GE and LE coexist with very little overlap in foraging behaviour and considerable overlap in prey type and prey size. LE and CE have high overlap in prey type and prey size and moderate overlap in foraging behaviour. CE and ME have high degrees of overlap in all categories. 4.4 Discussion Most studies that have compared use of foraging habitats, feeding techniques and prey selection have demonstrated some significant differences among the species. The findings of partitioning mechanisms based on feeding ecology suggest that there is probably little overlap in food used even amongst the aquatic feeding indigenous Egrets which nest together as their feeding behaviour is so different. The view is supported by studies conducted elsewhere on herons and Egrets. Diet differences among the four study species reflect food-niche differentiation. Analogous differences have been demonstrated in other studies too (Meyerriecks 1962 & Kushlan 1976, Murdich 1978, Rodgers 1983). These results are generally consistent with other published data and confirm some generalizations about foraging strategies and patterns of food niche differentiation among these four sympatric species. However the nature of differences has varied widely. Of particular interest in this regard is the interplay of foraging behaviour, habitat selection (Chapter 3) and prey selection (Fasola & Ghidini 1983). At Sheikha Lake four species of Egrets often foraged together in the same habitat but distinct differences in patterns of 76 \ ./ response to environmental change were identified among the gjfneVal foraging jDoiJuTatipn. Each species displayed unique foraging tendencies thus the n^ure' of sfoiagiti^^nii differentiation among this suite of ardeid species is multifaceted and may vary from region to region. Fasola (1994) discovered opportunism for a similar suite of European species generally taking advantage of locally available and abundant prey. Lowe-McConnell (1967) also studied three feeding herons on the Guyana offshore and described that Snowy Egrets paddle four or five together (probably family parties) on the edge of the tide where they were seen to chase and feed among small fish. The little blue herons feed scattered on the drier mud higher up on the foreshore, where they stand and wait for fiddler crabs. The tricolor heron was found to be a solitary feeder in Guyana, a lone bird crouches low, stalking along channels in the mud, running forward and shooting out the long neck in great suddenness to seize food, swallowing it immediately. Prey density too has been found to affect foraging behaviour (Draulans 1987). Smith (1995) has found dietary overlap between Great Egrets, Little Blue herons, Snowy Egrets and Tricolor herons and suggested that Great Egrets have high diet diversity as they ate a larger variety and size of fish species more than any other fellows. They also switch prey types as hydrological conditions and habitat availability changed and changed their foraging tactics to ensure continued encounters with preferred prey. For Great Egrets my findings are in conformity with the other studies. Meyerriecks (1962) has found open wing feeding in Egrets and herons and described and compared the feeding techniques of many species in great detail. He also noted the inter-specific feeding hierarchy based chiefly on size among those, which fed 77 together on the shore. On the Goto Donana in Europe Cattle Egrets were found eating mainly insects (Grasshopper, beetle, neuroptera larvae) spiders and small vertebrates such as frogs and lizards, but very few fishes. Whereas the little Egrets ate fish and aquatic insects and the night herons ate fish frogs and newts (Valverde 1958). Dimalexis et al. (1997) found Little and Great Egrets adopting different tactics and achieve variable foraging efficiencies. Little Egrets revealed greater plasticity in their foraging repertoire, especially with regard to their mobility and prey preference and Great Egrets consumed larger amounts of biomass per unit effort hence being slow feeders. Miranda & CoUazo (1997) have detected little or no dietary overlap amongst heron species proving advantageous for exploiting habitat that exhibit spatio-temporal fluctuations in prey availability. Opportunism may be the norm for these species but the available data suggest some common themes that my results help substantiate and are worth summarizing. Great Egrets are capable of foraging in deeper water (Chapter 3) and capturing larger fish - owing to larger body and bill size, than the smaller species but they exploit a wide range of prey item where the prey species also depends on this selecfion. Regarding foraging behaviour though they seemed to have specialized in walking slowly and standing and use almost 90% of their foraging time in this technique. The Cattle Egret has specialized in feeding on the ground besides grazing cattle and behind the ploughs hence its size and type of prey selection corresponds to terrestrial insects, yet it preys upon crustaceans and small fish too given a chance to feed near water. It also uses a wide variety of foraging behaviours with approximately equal thrust on some of them. The Little Egrets are specialized consumers of active medium sized prey hence they eat small fish and also 78 some molluscs and crustaceans. Depending on the prey selection it makes use of the walking fast and foot stirring techniques to the maximum but has been observed using other behaviors such as standing and gleaning too. The intermediate egret shows tendencies common to both the species it is flanked with on the classification axes - making an intermediary choice of foraging behaviours of the Little and Great Egrets and also exploiting prey items in the similar fashion (Fig. 4.1, 4.2, & 4.3). For instance if GE and LE use walking quickly 1.7% and 61.7% respectively of their foraging time then the figure for the median egret -31.7 falls in between these two. Similarly for prey type and prey size too the ME line in the figure runs between the GE and LE line in the line diagram plotting of percent values (Fig. 4.2 and 4.3) for most of the time. Thus ME exhibits the widest variety of prey selection and foraging behaviours and probably this can attribute to its population success (Chapter 3). Due to similarity in size LE and ME exhibit maximum overlap of resources in all state. Where as GE and CE stand far apart from them as well as from each other. However no combinations of the four sympatric species show complete overlap signifying absolute congruence, hence confirming niche segregation. For instance it is well evident that if there is high overlap in food size and prey type taken by ME and LE then there is very little overlap in their foraging techniques adapted for catching prey. It must be mentioned though that behaviour is commonly considered to be one mechanism of resource partifioning (Meyerriecks 1962, Jenni 1969, Recher & Recher 1969, Willard 1977), presumably based on the idea that Egrets hunting for prey in different ways are exposed to or can capture different prey. Indeed the species of Egrets under the scope of this study used different behaviours but they sometimes ate the same 79 prey - at times even the size of the prey was same. Whereas an association between behaviour and type of prey captured was demonstrated for the great white, cattle and Uttle egrets a species like median egret, which used only walking slowly and gleaning, ate the widest variety of prey item. Further research should consider differences in the diet due to selectivity on the part of the egret. It is hence propounded here that behavioural differences alone should not be considered to be the partitioning mechanism without also examining the effect of habitat, prey and prey size. Pianka (1974) and Schoener (1974) have suggested that for groups where more than one niche dimension is important, separation should be complimentary. For example a significant overlap for one resource should be offset by a difference in use of a second resource. Indeed in this study where little and large egret ate similar diet they varied in size of fish. Similarly there was not much difference between feeding behaviour of cattle and median egret they differed greatly in selection of prey item. It is useful to consider the extent of overall niche overlap (Pinaka 1974). If niche dimensions were independent (i.e. any behaviour is possible in any part of the habitat and for nay prey item) overall resource overlap can be considered as the product of the individual resource overlaps. Table 4.6 demonstrates the overall resource product for foraging behaviour, prey item and prey size for all species. However, if the resources were dependent (i.e. a behaviour occurs in only one part of the habitat and results in the capture of one prey type and size) then overall overlap can be considered the arithmetic mean which are given in Table 4.7. In this study the relationship between niche dimensions seem at least partially dependent. It seems that an appropriate measure of overall niche overlap lies between the 80 product and sum estimates. Thus we may infer that sum overall partitioning occurred among the four species in the present study. Most likely overlap among the species varies as their demand for resources relative to resource supply varies (Pianka 1972 and Rusterholz 1981b). A pertinent question is that why are these four species feeding in the same habitat and presumably having similar nutritional requirements using the food resources in different ways? Interspecific aggression may force a change in the foraging behaviour of subordinate species, thus altering the type or size of prey the species is exposed to or is able to capture (Morse 1974). A subordinate species would be expected to have a lower rate of net energy intake. However a mechanism of this nature requires a relatively constant dominance hierarchy. Caldwell (1979) has noted a hnear hierarchy between egret species. I have dealt with inter and intra specific interactions of four sympatric species of Egrets in a separate chapter (3) where aggressions and flocking have been studied together while performing different activities especially foraging, habitat use and roosting. Alternatively species-specific differences in foraging efficiency may exist perhaps due to slight morphological or physiological differences (Kent 1986a). Each species would then be viewed as eating a combination of prey that maximizes its net energy return. Comparable rates of net energy intake would be expected among the species. However, due to lack of funds and techniques available for ascertaining the feeding efficiencies of these species I could not include this aspect in the present study. Drawing from the outcome of the extensive studies on Camargue Little Egrets (Dugan et al. 1983, Kersten et al. 1991, Hafner et al. 1994 & Hafner 1997) what next is needed is further development. Some sort of interdisciplinary research programs could be developed to 81 investigate the link between hydrology, plants, prey and egrets foraging. Homogeneity constitution of feeding apparatuses across ardeid species in relation to their feeding behaviours (Dubale and Mansuri 1973, 1974, 1974a, and 1977) might also have a role to play. Perhaps more evident in my study is the differentiation on prey size but a much more integrated broader scale (in both time and effort) is needed to verify whether these species routinely and uniquely rely on any particular foraging technique. In particular variation in sample sizes across species, limitation of seasonal coverage, and a lack of replication across different regions may confound inter-specific comparisons of diet diversity. For instance in my study no species ate small bird or Great Egret was never seen eating a rodent and cattle egret was seen eating very little reptile where as there are confirmed reports of these species catching an occasional chick fallen from a nest, or Great Egret eating rodents and Cattle Egret feeding on lizards - sometimes even snakes (Hancock & Kushlan 1984 and Gassett et al. 2000) depending on food availability. Another limitation borne by this study was not identifying prey consumed by each species up to a higher level instead of an animal group. While the former requires either collection of regurgitated prey from heronries (Sodhi 1992) or gut-content analysis of birds shot a short while after ingesting prey (Sodhi 1989, Mukherjee 1971) or both (Sodhi 1992) only the latter could be commenced in this study as it was confined to non-interfering field observations alone. With the authorities getting stringent for wildlife researchers (Sethi 2005) and the intensive study area being a highly conservation sensitive spot (Pg 28) collecting a sample of considerable size for laboratory identification and analysis was next to impossible. Besides to maintain homogeneity over all seasons, collection of regurgitated prey item - which would enable investigation only during nestling period, would also have produced bias. However, under field observations it has been tried to reach upon the finest possible 'taxon' for prey identification. 82 *-> u QJ ISl) o 00 (N OO cn o O) Q. U 00 ^^ r<-i 00 r^ 2 o ^. TO e r-i 2 O ^ Q. :d ^ :5 5 E >- 3 ;3 a o >- •> t CO C/5 V) u Ml ON 00 o o o (N g ON ON o o o in •> 'O 3 o '•2 JD a. O) c Oi G (T3 i_ a O 1/3 00 O O 0) O 2 °0 00 >- o G ^ rsi O > o o| > i5 (U —' OX) o TD rtJ G E •, o P -C ^ o _o 3 T3 00 a 3 on c G O DO a 00 c _G OH 'S o "^ m O o o ^ O O o in vd o n en a in (N r~; ITl NO ON o ir> o iri '^f rn ON ON m o o u 00 bc r^ o lO o o o <^ ^ t< 2; o O o ft u on C/5 t/2 a c/3 Vi s 2 1 O IS oc 01 C/3 C/5 -4ii« 58 u CO o e ON -3 I/) a; u O) CL a u 44 in ^ Ml Q. 2 O E >^ 3 o (U N M) in ON 0\ M3 >• (V 1_ CL u N '&_ o E ^- ?2 3 wo rog o ^ ^ 2^ I I i > o o c ^ (U o g s CJ O C3 Ui LL CM 03 ID !E u re > 03 <->^ vo »-< (N iri c^'^ o ^ t~^ >n w JC m Tf v£> ^ o;^ CN (N in CO -C -ti u ro f i^ 'h a? 2^ S^ (N in 00 1-H 5 >*- •^ m •^ m u. fO 00 in IT) JD -o 00 00 (N ON •* >-H rf o 9 U i_ O c 5 o ?J ^ o QQ rsi in m ^ m m ON l> 00 1 00 f-H t-^ tt r<^ f^ ON V^O o Tt 1-^ o (N (^ rsi c i2 > ^ OJ -J TJ _l • • * 2i 2 ^ Ml a V -S « Js ja to 1- ro _i SI 01 .n. .a O O ON ON 00 O 00 Tf ^ri -^ O (N •M ^^ m ON lA) 00 r-- u i_ O) a; 'u Q. « w u •*ii» a O 01 (N in (N r- r^ r-- •4—t H ON r-- ro r-- o ^ Q. w 'd- ^ ON ^ 00 r^ E u OX) >^ S {/) o i_ V W c CD O (L) S 00 o ir-i ,—1 m ON m IT) w (M Tf ^^ NO r~- ON G « 00 00 r<-i (M IT) 00 2 Q. -3 OS i2 > o OuJ ^^. o§ Ofl W .'^ ^ £ o o «=> O H W W w W S •^^ O S -J MJ U S I Ofi 'u I W s r<-) (N O O r*-i OO .— if) !>• oo OS r-^ r^ O p rn CN O rn •^ a o — N e o u O ON ON ON OO O 00 ^ in TT O (N e •-H m ON in 00 r-- •a G ON a o .9 § Q^ T3 C a o J- ^ u Q.O "n c O > a (N r^ in c~- r-~ (N o •o o ON t^ r<-i r^ o •^ c Q ' ^ \D ON ^ 00 t~^ y0^) > r^ u Q. ro o h. w 00 3 oc C J3 ^ o — CU IK l-l PS w ci C fD rtJ o u S in ,_, r<-i ON rn in CN ^ .—1 NO r^ ON a OO 00 m (N in 00 JS > ^^ •'-' a 00 o3 {/) W CU O u 01 n3 3 .?^ 1_ o <-> O) W > (U CL U H S W W W W (U o IK HJ J a u DO I Co I a w g w w w a u o S o J u n 05 e ON ON in 00 ON ^n ON 00 m ON (N 00 93 ^ ^ r- •* r- r^ e o •a o w B •a O ON ON ON 00 O B 00 -"^ in '^ O (N a ^ m ON in oo r-- a. I. o t3 a w "u (U > a kH o (N r- >n r-- r- (N o n 00 J, U W g W w W H VI S HJ J u w I I a M U U u ^ [2} CZ5 U O ;^ O HJ U i 8- Ui a. u a. E 3 r i (1W QQ x: CO CO LU to JO LU fiT LL O o^ •5 + 00 U- E LU C3 E ^ 2 +oj ^ O o ^ LU 21 _l 2 g Q. ^*—' S •4-» 5 < + &0 LU pa O c o _i ^ 2 1 o o CM o C»-5 2o <0 bO pajnideo Aajd j^oi lo 86e)U30J9cl (U **- o (/) U •I-) ra Q. E CD > O >- < ro I LU to 00 CD 1n jS E LU w > o ^ o ro mwtmm a> 00 0) uoj)e)!0]dx8 86e;uaojaci O Q) U y is a. E ST o CO 5 U- iS ID Q- UJ CD •t-> ID i2 3 O LU o O •> o > (0 ID x: (a (D m c O) LU "o» CO C _l 2 D) £ (0 + i_ 3 O LU O u. •c o (D > O \ OS S o O PM "ID • O = o X •t; o • • m CO m s oooooooooo uo!;eoo||e QUiW )U30J3d CHAPTER 5 TEMPORAL DISTRIBUTION 5.1 Introduction In order to maintain peaceful coexistence with other inhabitants sympatric species distribute them selves over space and time in such a maimer that confrontations for competition are reduced to the minimum. For this they adapt themselves to differing time and energy budgets to reduce competitive exclusion in a way that each species thrives in its own niche etched out for its successful survival (Fuller 1979). In this chapter I have tested the above hypothesis with the example of four species of egrets living in the Sheikha Lake. Each species exhibits an optimal time budget for different environmental conditions and that natural selection favours individuals whose time budgets were most adapted to natural conditions (Vemer 1965). Piscivorous birds have been found responding to non-linear fashions to fluctuations in prey densities. As long as food abundance is above threshold levels they can maintain high levels of productivity over a wide range of prey densities by adjusting their foraging time budget (Burger & Piatt 1970) Egrets use a wide spectrum of non-breeding activities for their maintenance, which have substantial survival values for them. The norms of the extent of time spent in each of these activities, the time of the day chosen to perform them and also the seasonal variations between them may be observed by these species as a measure of partitioning mechanism. This chapter deals with such non-breeding daytime activhies - their regular patterns and time budgeting of sympatric egrets in Sheikha Lake. The main objective here is to identify a pattern of distribution over time and whether these species use it as a means of ecological isolation. 93 The behavioural patterns of animals are the product of their interaction with the external biotic and abiotic stimuli. Time or activity budget is quantitative description of how animals apportion their time for feeding or other activities (Baldassarre & Bolen 1994). Although some type of behaviour requires more time and energy than others, the optimizing paradigm predicts that the individual performs at the most opportune time (Smith 1976). Because of the chance component the underlying rhythm of any behaviour repertoire can be modified in most cases and therefore the behaviour pattern is probabilistic. Examining the influences of temporal and environmental factors on a species' time budge/ also enables us to understand the ecological significance of behavioural pattern (Boettcher & Haig 1994, Brady 1982). Many field studies have been undertaken on birds and small mammals as regards their time and activity budgets (Erkinaro 1972, Voute et al., 1974, Daan & Aschoff 1975, (Yahya 1980). There are existing studies on blackbirds (Orians 1961), wrens (Verner 1965), tufted duck (Folk 1971), finches (Schartz & Zimmerman 1971), hummingbirds (Wolf & Heinsworth 1971), geese (Raveling et al. 1972; Burton & Hudson 1978, Marquiss & Duncan 1994) european green-winged teal (Tamissier 1976), mallard and wood duck (Gilmer el al. 1977), peafowls (Navaneethakannan 1984), owls (Wijnandts 1984), albatrosses (Prince & Francis 1984), gadwall (Paulus 1984, Webb & Brotherson 1988), seaducks (Goudie & Ankney 1986), Canada goose waders (Eguchi 1988), (Eberhardt et al. 1989), jacanas (Betts & Jenni 1991), Black-necked Storks (Maheshwaran 1998), spotted owls (Delaney et al. 1999), common murres (Zador & Piatt 1999), keel-billed toucans (Graham 2001) and blue tits (Tripet et al. 2002). 94 There are several comparative studies on behavioral activity of various species also like raptors (Marti 1974 and Bosakowski 1989), albatross (Weimerskirch & Guionnet 1998), the bronze-winged and pheasant tailed jacanas (Ramachandran 1998), Wilson's and semipalmated plovers (Morrier & McNeil 1991), ducks (Sridharan 1989), waterfowl (Bhupathy 1995), and moorhens (Jayaraman 1985). Time and activity budgets of waterfowl have been studied by many authors (Morton et al. 1989). Analysis of activity budgets has been considered as a useful tool in determining the needs of post breeding waterfowl (Fredricson & Dronbney 1979). The activity rhythms are mainly regulated by light dark cycle of nature. Other extrinsic factors are temperature (Wiley 1971), sound (Menaker & Eskin 1966, Gwinner 1966) and social cues (Marimuthu et al. 1981). The intrinsic factors such as hormones (Turek et al. 1976) can also eventually modify several such activity rhythms. The amount of time and energy, which a bird devotes to different activities, must inevitably influence its survival (Orians 1961). Activity budgets of birds greatly vary according to the type of habitats and foods (Paulus 1984). They are also proposed to vary in correlation with prey availability and abundance (Cairns 1987, Burger & Piatt 1970 and Monaghan et al. 1994). Of late ecologists have been making an extensive use of time budgets and activity patterns (Gauthier et al. 1984) because these behavioural traits deal with potentially limiting resources common to all organisms' time and energy (Ettinger & King 1980 and Beidenweg 1983). Such studies have also been found specially suitable for comparative studies such as those between matched - sexes and periods; as well as unmatched pairs - across species and habitats (Holmes et al. 1979). The concept of time and energy budgets 95 ands its role in the annual and diurnal activity cycle has been recently developed by the contributions of several authors. The concept implies that the birds have to spend a certain amount of time in satisfying elementary needs of self-maintenance, above all in gaining sufficient energy for their metabolism. Behavioral defense mechanisms in response to parasites such as adjusting with time spent in different activities of foraging and maintenance have also been found to evolve given the fitness cost associated with ectoparasite infestation (Hart 1992, Christe et al. 1996, Perrin et al. 1996, Tripet & Richner 1997). Quantification of life-history characteristics is important in identifying the relationship between behavioural patterns and fitness, detecting and mitigating for anthropogenic impacts and understanding an animal's energetic needs under certain ecological conditions. Many investigations have quantified changes in behaviour of wading birds but few have examined comparable activity patterns of sympatric species. As far as egrets are concerned only limited studies are done exclusively on their energy budgets and activity patterns. I conducted this study for three years in the Sheikha Lake to quantify the behavioural changes in egrets in response to changes occurring in seasons, daily rhythms and presence and performance of other sympatric individuals. I examined the activity patterns of four species of egrets with the question that how they adjust these activity patterns according to daily rhythms and seasonal changes to work out temporal distribution. 96 5.2 Methodology 5.2.1 Data collection The study was conducted for a period three years spanning between August 2000 and March 2004. Based on the general observations on the activity of egrets and consultation of previous work on activity budgets of water birds in non-roosting hours during the off breeding seasons of the year I identified seven major types of activities that are performed by the four species of egrets under the focus of this study, these are as follows: 1.Preening: The act of cleaning and smoothening its plumage normally performed in between foraging or while siesta on a perch 2. Siesta: Seizure all activities during the day time 3. Resting: While egrets are foraging in the habitat they take intermittent rests doing nothing except preening occasionally. 4. Foraging: All the time that the bird spends in looking for food, handling it and finally eating it up. 5. Chasing While performing general activities egrets have been observed to defend their sites aggressively. In this bid they chase away other individuals from their territory 6. Display Before mating at the onset of the breeding season two individuals rise vertically to a few feet in the air with wings unfurled and before dropping back they stay at the peak of the rise for a moment. This spurt of two individuals male and female also includes bill- clattering, neck swaying etc. 7. Miscellaneous There are many short duration activities of egrets that cannot be classified under a particular term but they do take some time of their activity budget such as defecating, scratching the body with feet, tihing the neck and fluttering their wings. I record these activities under the miscellaneous type. 97 In the foraging grounds the individuals were observed with the help of a pair of 8 X 40 binoculars. The sampling method applied was focal animal sampling according to (Altman 1973) was applied. If the individual continued to perform a particular activity for 15 seconds or more, then the total amount of time devoted to that activity was calculated with the help of a stopwatch and recorded. Those activities that were performed for less than 15 seconds amounted in aggregate to the miscellaneous type. During the observation time if a focal animal flew away then the individual was changed (Yasmin 1995). The recordings were taken directly on classified data forms and later summarized according to temporal variations of seasons - winter, summer and monsoon. Total duration of an activity is rounded of to the nearest minute hence a duration is not expressed in the denominations of seconds. For example if an egret preened for 12 minutes and 48 seconds exactly then the time recorded as preening duration is 13 minutes. If the duration in seconds did not exceed the threshold value of 30 then they were not included in the records. For example if an egret rested for 12 minutes and 13 seconds exactly then the recorded observation time for resting was 12 minutes only. It was assumed that such adjustments would make-up for each other and will not produce bias in the results. Observations were made in three shifts of four hours each. The first shift ranged between 0600 hrs and 1000 hrs, second shift from 1000 hrs to 1400 hrs and the third shift from 1400 hrs to 1800 hrs (Lehner 1979, Yahya 1980, Maheswaran 1998). The beginning and termination time of observation however slightly varied depending on the variation of the time of sunrise and sunset. One shift of each type was devoted to an individual of a species of egret once a month and this way a full day observation was procured in every 98 month for all the four species. Data of approximately 285 hours of observation on the general activities of each species was subjected to statistical analysis. All the activity pattern observations were made on the Lake and not at the nest or the roost site. Different samples of the same season for one species were pooled and then the activity pattern for that season was plotted. Similar treatment was done for daily rhythms where a full day observation on activity patterns of foraging egrets were again classified into three shifts of four hours each namely morning. 5.2.2 Statistical analysis Data collected on the activity budgets of all fotir species of egrets at Sheikha Lake was summarized along with the temporal influences of the season year and time of the day. One-way analysis of variance (ANOVA) was used to test the Ho that 'the four species of egrets budget the time devoted to different activities in a similar fashion'. The Post hoc Tukey Test was performed to identify the differing samples. All the tests for the analysis of variance were done following Fowler and Cohen (1986). To compare the activity pattern of one species over three seasons - winter, summer nad monsoon, and over three shifts of the day - morning, noon and afternoon I used the Kruskall-Wallis test following Zar (1986). The Ho for this test was that a particular species of egrets does not distinguish between the seasons and shifts of the day in time and activity budgets. 12 k R,' KruskallWallis test statistics/f= Z -'3(N+1) N(N+1) '=' ni Where ni = the number of observations in the group i. k N = I] Hi (the total number of observations in all k groups) i=l Rj = the sum of the ranks of the n, observations in group i. All the data was analyzed by using the computer program SPSS 11.0 5.3 Results The percentage of time allocation on each activity by all four species representing an overall pattern of the year, in different seasons and hours of the day are depicted in the pie-charts 5.1 a, b, c & d; 5.2 a, b, c & d, and 5.3 a, b, c & d. Significant differences were found through the one-way ANOVA in the general time budgeting pattern of all four species regarding all the seven type of activities identified (Table 5.1). However, multiple comparisons reveal that preening time differs between all species except LE and GE. Only CE & ME and LE & ME differ in foraging activity. Resting time differs between CE-ME, CE-LE and CE-GE while siesta and time devoted to miscellaneous activities differ amongst all species. Difference occurs between display and chasing activity of CE-LE, LE-ME and ME-GE (Table 5.4a). Kruskall-Wallis test comparing the activity budget of a single species over the three seasons of the year - winter, summer and monsoon, and the three shifts of the day - morning, noon and afternoon reveal that the Cattle Egrets differentiate between seasons as well as time of the day for all activities at P<0.05 level of significance (5.5a). The Little Egret and the median Egret also adopt to different activity patterns for different seasons and times of the day except in timings of the miscellaneous activities over the seasons where, H = 1.777, P>0.05 and H = .076, P>0.05 respectively (Table 5.5b and 5.5c). However, the Great Egret exhibits differing activity and time budgets over the 100 three seasons but significant difference was not found in the preening activity of the species over the three shifts of the day where H = 7.305, P>0.05 (5.5d). Hence the Ho is rejected and the conclusion may be drawn that with minuscule exception all the four species of egrets resort to differing activity patterns as the seasonal changes in the climatic and consequent habitat conditions take place and also as the day graduates from dawn to dusk. Species comparisons of seasonal activity through one-way ANOVA (Table 5.2) reveal that the four species differ in their winter activity pattern for all the activities except chasing and miscellaneous type of behaviours where difference was not found significant as H = .125, P>0.05 and H = 2.311, P>0.05 respectively. While during summer and monsoon season time budgeting of all the species differed regarding all the seven type of activities. Post Hoc Tukey test done to identify the species that differed in activity patterns (Table 5.4b) shows that during winters all species except LE-GE differ in the preening activity. CE-ME, LE-ME and ME-GE differed significantly in their foraging time. For the resting activity only CE-LE, CE-GE and LE-ME differed significantly while for the rest of the activities in the time budget only ME-GE showed significant difference at P<0.05, level of significance regarding the siesta activity. During summer only LE-GE did not differ in their preening activity and the same was shown by CE-GE and ME-GE for the foraging time allocation. LE-GE showed similar trends of resting and miscellaneous type of activities in contradiction to the other sets of species. CE-LE, CE- ME and ME-GE differed significantly at P<0.05, level of significance, in their display behaviour where as CE-ME, CE-LE and CE-GE adopted differential budgets for chasing 101 during winters. For the monsoon season also non-significant difference in the preening time budget was found only between CE-LE and CE-GE and foraging time budget only between CE-LE. For time allocation to the resting, siesta and miscellaneous type of activities half of the sets of species differed significantly (CE-GE, ME-LE and LE-GE) and the remaining half performed without any significant differences (CE-LE, CE-ME and ME-GE). While there was no occurrence of display activity uniformly amongst all four species during monsoon significant difference at P<0.05, level of significance, was found between CE-LE, CE-ME and CE-GE regarding the chasing behaviour. Similarly species comparisons of daily activity patterns when divided into three periods of equal duration - morning, noon and evening through one-way ANOVA reveal differential activity patterns of four sympatric species of egrets corresponding to the changing hour of the day (Table 5.3). Significant differences at P<0.05, level of significance were found between seven activities comprising the time budgets of the four species for all the three shifts taken into considerations. Multiple comparisons within individual species done by the Tukey test for the changing daily activity of the four sympatric species of egrets exhibit that in the morning hours only ME-GE do not differ for the preening time allocation. All sets of comparisons between species show significant difference at P<0.05, level of significance regarding foraging and resting time budgeting for morning except CE-ME & CE-LE and CE-GE & LE-ME respectively. Time allocation to display and miscellaneous type of activities is similar only between CE-ME and CE-LE & LE-GE respectively. Chasing and siesta differ significantly between CE-ME, LE-ME & ME-GE and CE-GE, LE-ME & ME-GE respectively. During the noon hours all four species differ individually for preening and 102 miscellaneous type of activities except CE-GE. Similarly significant difference at P<0.05, level of significance was found amongst all species for Foraging and siesta between all sets of species except CE-ME. Time allocation to display and resting activity did not differ significantly between all species except ME-GE. However time budgeting for the chasing activity differed significantly only between CE-LE, CE-ME and CE-GE. Finally analysis of the afternoon hours activity pattern shows preening differed significantly amongst all species, while foraging and siesta did not differ between CE-GE and LE-GE respectively. Display differed significantly only between LE-GE and chasing time allocation was not found to differ significantly between any of the species. Significant difference at P<0.05, level of significance was found only between CE-ME and ME-GE for miscellaneous type of activities where as allocation of time to the resting activity in the time budget differed for CE-GE, LE-GE and ME-GE. An overall consideration of these muhiple comparisons leads to the conclusion that a vast majority of them are differences that exist between the time and activity budgets of individual species and in all cases of general, seasonal and shift-wise comparisons. Hence the Ho that all activity patterns are similar amongst four sympatric species over seasons and day shifts is rejected. This difference revealed by analysis may be accounted for a temporal distribution working within the species as a mechanism of resource partitioning over an important resource for survival i.e. time. 5.4 Discussion The significant differences in activity patterns of sympatric egrets over different seasons and shifts indicate that egrets with overlap in other niche factors such as prey species and size, foraging behaviors, and habitat may be isolating in terms of time 103 budgeting and that temporal distribution is also a means of resource partitioning adopted by these species to allow coexistence. This finding is supported by many other published works. Ramachandran (1998) has reported differential activity budgets of the bronze- winged and the pheasant-tailed jacanas in general as well as over seasons. Weimerskirch & Guionnet (1998) have found extensive differences in the foraging activity of fourteen albatross species occurring in the duration of bouts in flight, and on the water as well as in the frequency of landings and in the time elapsed between landings. Important differences in life histories of other homogenous groups have also been found (Pennycuick 1982, Warham 1990, 1996; Cherel & Klages 1998 and Weimerskirch 1998). In this study extensive differences were noted between the times apportioned to foraging and other maintenance activities by the four sympatric egrets. The cattle egret spent 66% of the total day time in foraging and the remaining 44% in the maintenance activities. This allocation was increased by two percent in the little egret with foraging time amounting to 68% and reduced to the minimum of 58% foraging time with the median egrets. The great egret spent 64 % of its time in foraging and devoted the rest to maintenance activities. Within the maintenance activities too break-up of time apportioning to different activities differed significantly. Amongst this preening time showed the maximum variation followed by resting time. Niche separation is operating within these sympatric species based on prey, foraging technique as well as time allocated to foraging. Individual comparison reveal that ME differs significantly from CE and GE in foraging time allocation because their foraging techniques are quite similar but food is different. While GE and ME specialize in unique prey types ME maintains a strong overlap on the prey types of both (See Chapter 4). 104 The four species showed a similar trend of devoting the first phase of the morning to foraging activity alone, as immediate compensation to the energy lost in the night is needed. But they differ in the total time devoted to foraging in the morning. Foraging time devoted by Little egret is the highest - 84% and least by the Great egret in the morning- 68%. The values for cattle and intermediate egret range between 76% and 79% respectively. Morning is followed by the noon period when all species give time to rest and digestion. In this period siesta occupies the largest chunk of the maintenance activities but species variation in this pattern again suggests partitioning over time. The cattle and the median egrets which are generalized feeders spend more time resting as compared to the Little and Great egrets which are specialized feeders. Longer foraging duration is again resumed in the evening at the expense of the resting duration by all species. The cattle egret spends the longest time on foraging in this period because it catches comparatively smaller prey and is smaller in body size too. Though the Little Egret too has a small body size it spends less time foraging in this shift as it departs latest to the roost site. The great egret with a large body size spends as much time on foraging as the little egret but departs early. The median egret, which is a consistent feeder, spends the smallest duration foraging in the afternoon as it accumulates enough night reserves in less time by feeding in a generalist manner. Although this study has not encompassed the breeding activities of egrets the data on the activity pattern into three seasons showed implications of the breeding activities undertaken. The winter season corresponds to the post-brooding period, the summers with the pre-brooding period and the monsoons with the brooding period of egrets. Display was recorded amongst all the species only during the summer season but there 105 was inexplicable variation in the time devoted to this pre-breeding activity. The little and the cattle egret spend 6% of their time in display where as the median and the great egrets spend only 3% of the total time in display. Although all the species need to build up body mass in preparation of breeding during monsoon they spend less time foraging in the summer. This is because water stretch in the Lake reduces during summers and increased fish density per unit area makes foraging efficiency higher. Interspecific differences in foraging versus maintenance time were recorded in summer attributed to various underlying facts like body size, foraging techniques, preferred prey item etc. Time spent on siesta is also maximum in this season. The great egret having the largest body size spends maximum foraging time (53%) in this season. Cattle egret is second in the series with 49% foraging time as it feeds on small sized insects. The Little egret spends a little less time foraging in summers as its foraging technique is faster than all other species. The median egret though spends least amount of time on foraging as it feeds on a variety of food items. During winters chasing time is increased by all species as presence of other waterfowl increases food competition. There is less difference in the winter activity of cattle, little and great egret as differential selection of habitat (See Chapter 3) and prey item minimizes food competition amongst them. The median egret spends less time on foraging due to its efficient foraging technique. During the monsoon season brooding is at its peak and activities like incubation and chick rearing, increase the energy requirements of the birds. Hence maximum time is spent on foraging in this season. Abundance of food due to high moisture content makes up for time devoted to nest attendance. Underlying differences in the time budgeting of this season would be more 106 clearly explained when a combined study on the breeding biology is taken up. Nevertheless these variations do suggest temporal distribution. The findings suggest that the general activity budget egrets is manifested upon prey availability, presence of other species and extant of the area foraged. That the amount of time spent in various activities varies according to seasons and daily cycles also suggest some compensatory behaviour related to the energetic requirements of prey searching - assuming that the birds spend the nights resting and digesting food to compensate for the day time activity. While in the foraging grounds the egrets may not roost or sleep but they do take rest-giving time for digestion of the food ingested. In addition to different interspecific activity patterns seasonal intra-specific differences in all species were also observed. Along with climatic adjustments this could also be attributed to different stages of the breeding cycle. The energy requirement of a bird rearing a nestling is assumed to be more than that of a bird fledgling (Ricklefs 1983). However during breeding they are constrained within their foraging range because they have to feed the chick regularly and therefore cannot got to distant zones for foraging. In certain cases the birds do not increase their foraging effort during their brooding period when they might be drawing on their body reserves to cover these additional requirements. Also prey intensities and thus encounter rates may be lower close to heronries and birds brooding may be less successful when constrained to forage near closer to the heronries. Any future study can throw more light on the phenomena. Intra-specific activity patterns were found to vary between different times of the day. These differences may be indicative of the precision of the biological clock underlying and governing such activities that constitute the time and activity budget. Such differences were also noted between different species and may be attributed to the inherent sensitivity of the bird to the light intensities. Nevertheless conditions of temperature, atmospheric humidity and consequently prey availability are also dependent on the light intensity and these factors coupled with the circadian clocks of the egrets might determine temporal redistribution of the activities within the time budget of the species as light intensities change. Opportunism may be the regulating mechanism behind the temporal adjustments described above. Adaptive significance of time and activity budgets have been reported by many other authors too (Furness & Barrett 1985, Cairns 1987, Burger & Piatt 1970, Monaghan et al. 1994, Utley et al. 1994). Common murres have been reported to spend more time attending breeding sites when prey is abundant. Conversely when prey is scarce they increase the amount of time spent foraging at the expense of time spent ashore (Monaghan et al. 1994). Graham (2001) has found Toucans devoting similar time to perching and feeding in disturbed habitat and suggest that combining activity budgets of birds with habitat selection yields a better understanding of factors that allow populations to persist in disturbed habitats. Navaneethakannan (1984) has reported a positive relationship between various activities of peafowls and length of the photo period. Statistically significant differences as well as similarities were found by Ramachandran (1998) within the seasonal activity of jacanas also. The finding that display is given more time in the pre-breeding season than others is also reflected in prioritization of the activities. It was observed that in the pre-breeding season egrets resort to display activity first thing in the morning. A mixed flock of all four species consisting of 40 to 50 individuals indulged in prenuptial display for one hour 108 soon after making it to the Lake. However foraging was resumed after this and though the same pairs remained in close proximity of each other there was no further display. Where as in breeding and post-breeding periods foraging was started first and went on uninterrupted for at least two hours soon after emerging from roost. This supports the view that most organisms apportion their time for different behavioural activities. The optimal budgeting of time and energy between foraging versus non-foraging activities is, evidently, profoundly influenced by the circadian and seasonal rhythms of physical conditions, as well as those of prey availability. The availability of nutritious food, suitable habitat and environmental factors (Temperature, rainfall) explains the difference in seasonal time allotment for feeding and maintenance activities for all the four species. In species where this difference is not very pronounced time spent on contingencies may have masked the patterns by redistributing the temporal order of normal activity (Campos & Lekuona 1997). Brady (1982) states that the circadian control of the daily repeated, normal ongoing behaviour rhythm should only be represented as probabilistic average, and does not prevent animals from making instantaneous ad hoc responses when the need arises. Nevertheless the time budgets amongst egrets are influenced by habitat conditions, food choice and availability, and environmental factors. Replication of such study in other locations is needed to determine the general applicability of these patterns. Finally variation in prey availability and abundance in the foraging grounds may influence time and activity budgeting pattern. An understanding of food availability and abundance may help clarify causes underlying the patterns observed during this study. 109 o o o o o o o o o o o o o o o u V -< a > in 00 \or^ vo S (^ 00 0 (N ^ LI Ti- °o 00 00 ii o 00 00 (N s '^- ku. UD in o U in o (N ••-> r-- u« u o M3 o ON .2 • bi) fS ON (N 00 00 2; o 00 r- (N (N '^ bX) t—< (N 00 O ^ iri o o ^ m ON o r-~- o r-i '—' ^—^ in '* »—' CO 3 oaj G 00 Of) C3 c c 00 >% 00 2 '3) _c rt -2 fi aj (U CS t/i Cfl f> *-C/^3 "C/al cd tn O .H J3 o X tin Di c^ 5 H o O o ON o 00 ^•< 0N o o o O < o ON q q q q ^ q « o Z ON O in c Z b (N ON NO r-1 o O < 00 NO rn o o o in in (N 1^ a u ^ ^_ in rn r~; r<-i o © ON NO 00 ^ r-^ o fN o s m M3 co 00 NO o NO ON 00 o 00 (N CNI NO 00 NO rn o r-i 00 »—' ON ^^ fs u o (N o6 B ^ ^ ^^ (N (N r- O O o o o o O R 0. O o o o < o o en q q q q z q q S ^ ON r~; r^ < ON ON W m in in •* ^ <2i O < CNI ta Z w •3 00 in U in o o O 00 o o a (N in ^^ (N r- 'u c DC in s ON o NO o o o in in •** ii B in ^_ in bc B r- o o in o 00 r<-i o o Ps3 rf NoO (N >—' r<-) r- tlT 00 in NO o O NO o (N u r<-i NO ^ od ^^ t~- DC ^ O O o O o o o w '^< fiu, O O o o o o o c q q q q q q q -5 i 0 r<-i OJ fi Z yr\ m 00 >—; 00 b ^ in NO (N S o ^ ^ CNI ON -- U o NO Tj- O o o O r~- ON ON in O DC ON 00 I. U ON in NO o © ON 00 in ON o B S NO 00 fN ^ U (N o o NJ o u o o o 00 NO in r-~ ^^ u NO DC GO w U H - > NH H >' OH (73 Q o o o o O o as < o o o o O o o > p p p p p p p I O u 00 in in z o (N O < o 'O s 'NO O o ON r-- 00 o o O rn in 00 r-- NO in o (N 'S rNi ^ NO OS Os r^ U in (N o -^ (N ^ ^ m in in NO 00 r~- in ON ON ON rN) ON o o o O o o o o o o O o o o < p p p p p p p 0) > I (N NO S o ON in O o 00 in O ^ in ON rn NO in r-^ o •o (N G o (N 00 in o o O 00 o 00 ^ CN) +-* •a ON iri <-<-) o o OX) B ^ O W NO o ON I p 00 CM 00 •o r-i ON O o a m in o ON ro ON I (N ^ in NO ON 'NO in (N (N &X) O o o O o o o W o o o O o o o o p p p p p p S -a in B Z NO in p r-- in r-^ ON >o 00 in o < in r<-i W NO in p 00 NO in O ON ON 00 ON 00 r~; u in CNJ e _B in 'a s 00 o in u u NO oo in 00 ON NO in u o (N NO O in o (N iri 00 00 in o ON 5 00 ON H * IK o lO O 00 o O o (N if) H o o (N (N IT) m s I H w o X 4f- * 4f- •** * *t^ * o r- r1—-1 r- m o lO ^^ >o ^ 00 OS in I 0r0- (N >o '>r-^i vo -H r- t-- —' t^ (N W O •*-» I 00 k. CZ5 * if- W w * r-- * * 00 r- O t^ en o 00 f—1 a I O^^S o '^t m o o o ^ 00 o 00 r-- o in ron6 vO 00 u o 1 r<) w C 0) > 00 u * * * * en m o o^ mo c c 00 00 in O o o (N ^ § ^ u 00 o ^ ^ ^- OS c o * ro * * * * 00 O * m 00 '""' m i/^ 00 I OS m OS r- o -* r-^ r^ W 00 — 00 'S^ 2: ;^ o u 1 (N on O -(—» C DC QC (U C 00 >> M 00 g CT3 ^ 2 '5b g c/3 o Mean Difference in Seasonal Activity among species (Post Hoc Tukey Test) Activity Species CE-LE CE-ME CE-GE LE-ME LE ME-GE GE Winter Preening 43.25* 151.125* 64.75* 101.875* 21.5 86.375* Foraging 13.75 122.5* 7.25 108.75* 6.5 115.25* Resting 36* -25 57.5* 36.25* 21.5 57.75 Siesta 00 21.5 7.25 21.5 7.25 2875* Display 0 0 0 0 0 0 Chasing 25 00 00 25 25 60 Miscellan 7.25 7.37 7.25 14.625 14.5 .125 Summer Preening -54.7500* -117.5000* 12.000* -63* 66.75* 129.75 Foraging 36.25* -29* -19875 -65.25* -56.125* 9.125 Resting 32* 85* 44* 53* 12 41* Siesta 0 0 0 0 0 0 Display 13.75* 17.125* 7 3.375 6.75 -10.125* Chasing y* y* y* .000 .000 .000 Miscellan 25* 19* 19.125* 16* 5.875 10.1250* Monsoon Preening 5.875 94.5* 6.125 88.625* 12* 100.625* Foraging 1.75 90.625* 55* 92.375* 56.75* 35.625* Resting 17.625* 3.75 31.875* 21.375* 14.25* 31.625* Siesta .75 8.625* 92.00* 7.875* 92.75* 100.625* Display 0 0 0 0 0 0 Chasing 8* 8* 8* 00 00 00 Miscellan 18.625* 9* 9* 9.625* 9.625* .00 *Mean difference is significant at 0.05 level Cattle Egret (CE), Little Egret (LE), Median Egret (ME), Great Egret (GE) 114 Table 5.4c: Differences in daily activity patterns amongst four sympatric species of egrets at Sheikiia Lake (2001 - 2004) Mean Difference in Seasonal Activity among species (Post Hoc Tukey Test) Activity Species CE-LE CE-ME CE-GE LE-ME LEGE ME-GE Winter Preening 6.9167* 9.8333* 12.9583* 16.75* 19.875* 3.12 Foraging 12 7.5 22.54* 10.5417* 34.54* 15* Resting 14.5833* 14.5833* 0 0 14.5833* 14.5833* Siesta .1250 .0833 7.2083* .0417 7.333* 7.2917* Display 9.667* 1.9583 4.2917* 11.6250* 5.3750* 6.25* Chasing 1.6667 9.8750* 1.75 8.2083* .0833 8.125* Misceiian 1.708 4.4583* 3.6667* 6.1667* 1.9583 8.125* Summer Preening 24.4583* 30.5833* 2.7917 6.1250* 21.667* 27.7917 Foraging 15.3333* 7.6250 22.3750* 22.95838** 7.0417 30* Resting 17.5833* 25.5833* 28.5833* 8 11* 3 Siesta 13.8333* .9583 9.7917* 14.7917* 23.6250* 8.8333* Display 3.4167* 2.4583* 2.4583* 5.8750* 5.8750* 0 Chasing 2.1667* 2.1667* 2.1667* 0 0 0 Misceiian 9.6250* 6.2917* 1.75 15.9167* 7.8750* 8.0417* Monsoon Preening 9.0417* 41.75* 2.9583* 32.7083* 6.0833* 38.7917* Foraging 15.4583* 46.25* .500 30.7917* 14.9583* 45.75* Resting 1.2917 3.2917 11.1667* 2 9.8750* 7.8750* Siesta 5.4167* 5.25* 11.5417* 6.1250* .1667 6.2917* Display .9583 .7917 1.9583 1.75 2.9167* 1.1667 Chasing .8333 1.7917 .9167 .9583 .0833 .8750 Misceiian 2.1666 5.1250* .0417 2.9583 2.1250 5.0833* *Mean difference is significant at 0.05 level Cattle Egret (CE), Little Egret (LE), Median Egret (ME), Great Egret (GE) 115 ^ O o o o o o o O r-H O o « O O o o .s o o o o o o u CM ON m OS o oo in ON ON o W izi c« o in iri o< 00 ON ON in in --^ m > m in ;£ in in o ^ •"1 •^ ON ON ON 00 r-~ in OX) -H ^ (N ^ rn ON c 'S c ON ON o m in \o o > o V .a o< in -a Z c c 00 oo 00 o s o in ^O ^ o o ON WD o (N o^ ^ -H 0;::0; — (N S o o o o o o 00 o o o o o o o o o o o o o o c O CM o c ao a> s in 'NO in ON •r: .i^ ^ •** o in 00 o in en c 00 ON ^ t>- o '^ ^ o o e o (N r-- —< 00 o (N O ^ 00 00 c ? o G in o r-~- « ^ ^ 00 in o GO « ^ O vo ^ rNJ n-1 ^ Tt 00 s o o ri o I OO iS ^ ^ in r- ;_; CO rr\ r-^ ^^ c M • 1—( ^ G I 'S § 5 -S -S o [/3 en o B t/3 U o o o o o o o o o o o o o o o o o o o o o o o o u irsi 0^ as _j ON OS p ro jilt p 00 00 00 ^ JZ IT) j^ •(U JZ U) •l-> a» OS OS o (T3 IT) >o m r4 (N >^ > •a S in OS 00 p oo o O 00 o c 00 OS m o W V5 E/l 5, ^ 00 5_ O > giS IT) lAi 5 00 r-- so (N >ri 04 rj ^ •^ rsi > c 00 00 DO o 00 O o o o o OS g C/3 Z > e oo Os OS OS rsi r- o 00 IT) rsi o G (^1 O O s C S •3 s .A o o o o o O m « o o o o o O so o o o o o O Os o O 00 c g o 00 f- ir-i r~- T—1 sc •« -^ ^ '* CN o (N SO Tsof f<-) 00 (N 00 t-~ o >• 3 ;r; —I SO in iri 00 (N -H —< -^ c o o c o t~- 00 OS so 00 ^ c e o *^ ^ so in ? IK o OS ^ O ro o 00 55 (N ^ ^ o ^ in B •^ OS in oo O 3 OS 00 so t/5 3 OS rn in OS DC OJ) G g 00 >:> 'a '3) _g CO i2 CC *+-* !/3 cd in O i S <« U in ON -s -2 ^ (N o o in 00 rn « i» 2 IT) > s s in x: ON 00 o s o a 00 in 3 cn o GO a 00 ^ :£:: 2 a CN in -^ o ^ in 00 MISCELLANEOUS MISCELLANEOUS 3.0% SIESTA SIESTA 7.0% PREENING 5.0% DISPLAY 3.0% RESTING RESTING 2.0% DISPLAY 14.0% 10.0% 1 CHASING 4.0% ^J. ^0% ^ 1 CHASING ^BL ^0% Cattle Egret Little Egret MISCELLANEOUS 3.0% Median Egret Great Egret 120 Fig 5.2 a, b, c & d: Allocation of time to different general activities during the summer season by four sympatric species of egrets at Sheikha Lal MISCELLANEOUS MISCELLANEOUS 4.0% 5.0% SIESTA SIESTA 9.0% PREENING 10.0% RESTING 11.0% RESTING 20.0% 1 DISPLAY 15.0% ^J^ 6.0% ^^^^^ CHASING J^ Cattle Egret Little Egret MISCELLANEOUS MISCELLANEOUS 3.0% 3.0% Median Egret Great Egret 121 Fig 5.3 a, b, c & d: Allocation of time to different general activities during the monsoon season by four sympatric species of egrets at Sheikha Lake(2001 - 2004) MISCELLANEOUS MISCELLANEOUS 4.0% S.OK. Cattle Egret Little Egret MISCELLANEOUS MISCELLANEOUS 3.0% 3.0% PREENING 18.0% Median Egret Great Egret 122 Fig 5.4 a, b, c & d: Allocation of time to different general activities in the winter season by four sympatric species of egrets at Sheikha Lake (2001 - 2004) N«SCEl.U»iEOUS 4.0% MISCELLANEOUS 50% Cattle Egret Little Egret MISCELLANEOUS MISCELLANEOUS 30% 3.0% SIESTA 5.0% RESTING PREENING 8.0% 27.0% \ ] CHASING Hlf 3.0% FORAGING 66.0% ^^^i*s^v^ Median Egret Great Egret 123 Fig 5.5 a, b, c & d: Allocation of time to different general activities in the morning period by four sympatric species of egrets at Sheikha Lake (2001 - 2004) MISCELLANEOUS MISCELLANEOUS 3.0% 2.0K Cattle Egret Little Egret MISCELLANEOUS MISCELLANEOUS 5.0% PREENING 1.0% SIESTA 9.0% aESTA PREENMG 1.0% DISPIAY 4.0% 12.0% RESTING Z0% RESTING DBPIAY Z0% CHASING 8.0% 5.0% 5.0% ^^^M CHASING Z0% FORAGING FORAGING 76.0% 68.0% Great Egret Median Egret 124 Fig 5.6 a, b, c & d: Allocation of time to different general activities during forenoon and afternoon period by four sympatric species of egrets at Stieikha Lake (2001 - 2004) MISCELLANEOUS 2.0% MISCELLANEOUS 7.0% Cattle Egret Little Egret MSCELLANEOUS PREENING 50% 100% 80% 150% y^ \ SS^ RESnNG ^^^^^^^ \ uo% ^^r '^ >^-f--VjW FORAGING 590% Median Egret Great Egret 125 Fig 5.7 a, b, c & d: Allocation of time to different general activities during evening period by four sympatric species of egrets at Sheikha Lake (2001 - 2004) MISCELLANEOUS MISCELLANEOUS 2.0% 5.0% Cattle Egret Little Egret MISCELLANEOUS MISCELLANEOUS 3.0% 3.0% Median Egret Great Egret CHAPTER 6 ROOSTING BEHAVIOUR 6.1 Introduction Roosting is one of the important behaviors of the birds in which they spend almost half of their daily cycle. Little is known concerning the specific functions of communal roosting and flocking of birds beyond a probable advantage of reducing the risk of predation through increased predator detection or evasive behaviors unique to groups (Sparling & Krapu 1994). In some species of birds communal roosts may serve as information centers increasing foraging efficiency (Ward & Zahavi 1973, Bayer 1982, Waltz 1982, Stutchbury 1988). Foraging efficiency can also be increased through local enhancement (Hinde 1961) or use of alternative diurnal roosts (Caccamaise & Morrison 1986, 1988). A number of bird species of diverse orders and families with a diversity of habits and habitats roost together for at least a part of the year. In a few cases such social roosting may be a simple consequence of the parent bird with suitable roosting sites forcing these birds to roost together. However, in a majority of cases of communal roosting the birds associate together through some social attraction and do not disperse even if alternative roosting sites are available. Some of these social groups merely comprise feeding or migratory flocks, which remain together outside the roosting site as well. A number of avian species are reported to voluntarily form new social groups specially at the time of roosting (Gadgil & Ali 1975). Although a number of accounts of the Indian birds make incidental references to the roosting habits no systematic account of this phenomenon has yet been presented except, Razack and Naik (1965), Gadgil & Ali (1975), Mahabal and Bastawade (1985), Yahya (1987), Mahabal and Vaidya (1989) and Sivakumar et al. (1990). In fact various published accounts of communal roosting are 127 all based on examples selected to illustrate a particular point and not of an account which deals with the avifauna of an entire region (Wyne-Edward 1962, Ward 1965, Seigfried 1966, Zahavi 1971, Gadgil 1972, Ward & Zahavi 1973, Venkatraman 1996, Tarburton & Kaiser 2001, May and Gutierrez 2002). Many species of birds roost communally year round and breed in colonies. Some use communal roosts only during non-breeding season and breed in isolation solitarily at all times. It is well recognized and a number of interesting suggestions have been made as to the nature of the advantage conferred on birds participating in communal roosting to explain its adaptive function. a) It enables birds to conserve heat (Bremmer 1965, Francis 1976, Walsberg 1986) b) Communal roosting enables birds to assess population densities, which are then adjusted to the prevailing level of food supply through emigration and adjustment of reproductive rate (Wynne-Edwards 1962). c) Communal roosting serves the function of communication of information regarding the location of food sources (Krebs 1974a, Bayer 1982, Weatherhead 1983). d) It enables birds to reduce the risk of predation (Zahavi 1971 & Flemming 1981). But Gadgil & Ali (1975) do not agree to the first two hypotheses as smaller birds that are more susceptible to heat loss due to greater surface to volume ratio, are less inclined to communal roosting, and population regulation by this method has been found inconsistent to the principle of natural selection. However, they support the latter two as the most significant functions of communal roosting but call for more evidence through research. 128 Ardeid coloniality too is suggested to be an anti-predatory behaviour. The importance of roosting in a large compact group on trees is a defense from ground predators. The efficiency in locating food is promoted by communal roosting as information centres, which is a primary function whereas adaptation against predation is a response to increased predation pressure consequent on the assemblage of birds. The adaptive significance of flocks is pertinent and the predator avoidance may be an important function of communal roosts. Others however, do not seem to agree. Egrets do not seem to exhibit anti-predator behaviours such as mobbing to the same degree as other colonial species (Milstein et al 1970, Seigfried 1971b, Krebs 1974b, 1978; Mock 1981, van Vessem & Draulans 1986 and Rodgers 1987). Foraging herons learn about the location of good foraging areas by following successful herons from the colony (Bayer 1981). The flocking behaviour as an adaptation to improve the location of food has surely evolved in response to unpredictable spatial and temporal changes in food conditions (Barnard 1980, PuUiam & Milkan 1982, Pulliam & Caraco 1984, Barnard & Thompson 1985 and Krebs et al 1992). Studies on roosting behaviour of birds specially water birds are scarce. In fact based on my literature survey I may reckon that this intriguing aspect of avian is least studied, especially in India. In case of egrets it becomes even more interesting as they are communal roosters. A comprehensive search on published studies on herons and egrets reveals that hardly any study has been conducted on comparative roosting pattern, pre- and post- roosting behaviour and the roost site selection of sympatric egrets. In the present chapter I have made an attempt to explore variations related to the roosting activity amongst sympatric egrets in my study area. 129 The knowledge of roost site characteristics of sympatric egrets or any other group of birds may lead to a better understanding of their habitat requirements and help to evaluate the suitability of an area to support their populations (Churchill et al 2000). The roost site selection plays an important role in the thermoregulation of birds especially in the winter night, which is the most thermally stressful part (Walsberg & King 1980). This again asserts that selection of appropriate microclimates is generally thought to be an important component of the avian behavior. At the Sheikha Lake, Aligarh, the four species of egrets were found using clusters of trees near the Lake for roosting with other water birds such as little cormorants, black- headed ibis and glossy ibis. I compared the roosting patterns based on emergence and settling from the roost site, pre- and post- roosting behaviours and selection of roost site characteristics of sympatric egrets to investigate the presence and extent of methods of niche partitioning amongst them. 6.2 Methodology 6.2.1. Data collection In an attempt to determine as to which variables are important to roosting egrets I compared vegetation characteristics at roost sites selected by the four species of egrets. After some sites were located around the Sheikha Lake searches in areas with similar roosting habitat characteristics were also carried out. Observations on the roosting pattern, roosting behaviour and selection of roost site for the four sympatric species of egrets were made on 191 occasions during the breeding as well as non-breeding seasons of egrets for the years 2001, 2002, 2003. The egrets are not seasonal roosters as some of the other communally roosting species but they roost on a constant basis (Gadgil & Ali 130 1975). I tried to devote equal observation occasions to the roosting events of egrets at dawn as well as at dusk. Roosting pattern - Observations were made one hour before sunrise and one hour before sunset until all emergences and arrivals were complete. Meteorological data such as time of sunset and sunrise were collected from various sources (Chapter 2). Time of emergence and settling, total time span of settling to roost and emerging from roost, roosting time and flock size of arriving or departing egrets were recorded. Roosting behavior - Pre- and post-roosting activities were noted through the scan sampling method following (Altmann 1973). At a fifteen-minute interval total number of individuals of a species performing a particular behaviour were counted and records were maintained by converting into percentages of total individuals counted (Draulans and van Vessem 1986). Various pre-roosting and post-roosting activities in egrets were identified: Hopping: The birds change many places before finally settling down. Similarly before emerging also they hop around within the tree, since most roosting sites are woodlots or a cluster of trees some times this changing of place also results in change of the tree. Hovering: Although egrets are not capable of hovering one place precisely like terns or kingfishers I have grouped the particular act of egrets encircling the roost site, and flying slowly in circular paths close to the crown of the trees as hovering. Fighting: Individuals of all four species often engage in inter- or intra- specific fighting within the roost site for better place. Chasing: Some times this fight leads to a chase where the defender of a space chases away the intruder. 131 Calling: A cacophony of sorts is created by all species of communal roosters arriving at a site for settling down or before leaving the site for the day. This type of noise was recorded as a pre- or post- roosting activity Roost site - The area used intensively for roosting was designated as the primary roost site and compared with the available area. At these sites structural characteristics of roost trees such as tree height, girth at breast height (GBH), canopy cover and species were noted. I used the Point - Intercept method for estimations of vegetation cover and expressed it on a Braun-Blanquet (Causten 1988) cover scale of five ratings - (+) for cover very small; (1) for plentiful but of small cover; (2) for 5 to 20% cover; (3) for 25 to 50% cover; (4) for 50 to 75% cover; and (5) for more than 75% cover. Point Centre Quadrat method was used to determine the density and species composition of the roost trees. All trees with more than 10 cm GBH were enumerated and measured. 6.2.2 Statistical analysis Since the sample size was large enough, the bivariate Product Moment Correlation Co-efficient (r) was calculated to find the significance of correlation between total roosting hours and day length and corresponding to time of sun-set and sunrise. Mean values of both variables have been plotted in a scattergram to test whether the nature of correlation is positive or negative. n L xy - E X Ey r = V{n. Ix^- (S X) ^} {n. Zy ^ - (Sy) ^} where n = the sample size X = the first variable 132 y = the second variable The Mann - Whitney U- test was used to compare the differences in use of roost site and roosting behaviour by the four sympatric species of egrets. The following test statistic was followed for estimating this difference: n2(n2+ 1) ^i = n, . n2 + — -R2 2 til (ni + 1) t/2 = ni . n2 + — -Ri Where ni = sample size of first variable n2 = sample size of second variable Ri = the sum of the ranks of sample 1 R2 = the sum of the ranks of sample 2 Since ni and n2 in this study are far greater than the threshold value of 20 it was found appropriate to convert the smaller value of [/ to a z - score, corresponding to a normal curve with the help of the following formula U-{n\.ni)l2 Vni. n? (ni + n? + 1) 12 All the calculations were done using the simulations of the computer program SPSS 11.0(2001) 6.3 Results Analysis of roosting patterns shows that emergences for all the species from the roost site are positively correlated with the time of sunrise (for Cattle Egret r = .991 at P 133 - 0.01, for Little egret r = .766 at p = 0.01, for Median egret r = .970 at P = 0.01 and for Great Egret r = .899 at P = 0.01;) which renders the statistical conclusion that the correlation between emergence of all four species of egrets from the roost sites with that of the time of sunrise, is highly significant Figure 6.1 a, b, c, & d). They begin to emerge approximately one hour before sunrise and continue to do so upto 15 minutes after sunrise (Table 6.1). Similarly the arrival of the species to the roost sites for settling to roost is also positively correlated with the time of sunset (for Cattle Egret r = .980 at P = 0.01, for Little egret r = .996 at p = 0.01, for Median egret r = .966 at P = 0.01 and for Great Egret r = .899 at P = 0.01;) on the basis of which we can interpolate the statistical conclusion that the correlation between arrival of egrets at the roost sites with that of the time of sunset is highly significant (Figure: 6.2 a, b, c & d). Arrivals begin about ten minutes before sunset and continue for about half an hour after sunset until all four species have arrived (Table 6.2). In both cases of emergence and settling the time of sunrise and sunset which changes on a gradient over various months of the year is the independent variable and the time selected by the birds for emerging from the site in the morning and settling for roosting in the evening is the dependent variable. As a consequence to the positive correlation of arrivals and departures with that of sunset and sunrise time respectively, the total roosting hours of the four species also depended on the movements of the Sun. Hence a negative correlation has been found between the total day length i.e. time span between sunrise and sunset time and the total roosting hours of the egrets. (Figures 6.3 a, b, c & d). Analysis reveals that the correlation 134 between the variables - one dependent and the other independent is highly significant (for Cattle Egret r = .699 at P = 0.05, for Little egret r = .854 at p = 0.01, for Median egret r = .856 at P = 0.01 and for Great Egret r = .866 at P = 0.01). Hence it can be concluded that for all the four species of egrets as the day length increases the total roosting hours decrease (Table 6.3). When comparisons (Table 6.11) were made between the roosting patterns of the four species using the Mann-Whitney U test it was found that highly significant differences exist between the total roosting hours, emergence time and settling time of all four species. Significant differences were also found in the total time span taken in settling and emerging by the four species. Similarly highly significant differences (Table 6.11) were also found between the pre- and post-roosting behaviours adapted by the four species before they settled to roost for the night or emerged from the roost sites (Table 6.4). However, when the selection of roost site characteristics by all the four species was compared (Table 6.12) no significant difference was found amongst them. (See Table 6.5 for ground cover, 6.6 canopy closure, 6.7 canopy level, 6.8 for tree height and 6.9 for girth at breast height). Hence we may conclude that the four species of egrets under the scope of this study do not hold any distinction between various categories of ground cover, canopy closure, canopy level, tree height and girth at breast height of the roosting site while roosting communally. 6.4 Discussion It appears that a definite relationship exists between the movements of the Sun and the roosting activities of the egrets. Similar results have been ascertained in several 135 other birds too. Such relationships have been observed in house swift (Naik and Razack 1967), Blue Magpie (Hosono 1967), Green bee-eater (Bastawde 1976), Rosy Pastor (Mahabal and Bastawde 1985), Common Crane (Alonso et al. 1987), Barbets of Megalaima Genus (Yahya 1987) and Common Myna (Mahabal and Vaidya 1989). Amongst egrets and herons too earlier studies depict this relationship for Cattle Egret (Seigfried 1971b), Great Blue Herons (Bayer 1981, Mc Neil et al. 1993 and Benoit et al. 1993) Grey herons (Vessem and Draulans 1987 and Seibert 1951) and Egrets and Herons (Sivkumar era/1990). The actual physical stimulus influencing the roost pattern amongst egrets may be light intensity (Siegfried 1971, Counsilman 1974, Razack & Naik 1965) but since it was found in this study that cloud density did not largely affect the emergence and settling of the egrets, it may be concluded that changing envirormiental factors alone do not account for changing roosting rhythms. There might be an endogenous rhythm too in the form of the circadian cycle (Aschoff 1965, Gyllin 1967). While comparing the individual roosting patterns of the four species I found differences in their respective roosting hours. The different emergence and settling times may be an indirect factor for ecological isolation. The late emergence of Great and Little egrets from the roost may be attributed to the fact that they followed other successful species to feeding grounds (Krebs 1974a) Birds typically restrict their foraging to day light hours and therefore must rely on stored energy reserve to survive overnight. This period of fasting often coincides with the peak thermostatic demands that may occur on relatively long and cold winter nights (Walsberg 1986). The time at which birds settle down to roost and depart depends on several factors. The delayed onset and termination of activity in birds are related to light 136 intensity. Earlier authors held the view that birds are awakened by species specific light intensities (Seibert 1951). Soon it was known that light intensities, which initiate activities, (usually vocalization) in the morning and stopped activity in the evening were systematically different from each other. This was subjected to variations in season and the functional states of animals (Zimmer 1919). Many bodily functions of organisms oscillate rhythmically and keep pace with geographical temporal order (Bunning 1973, 1982). In higher vertebrates the main entrancing agent is the natural light-dark cycle (Aschoff et al 1982). The loco motor activity is best suited to demonstrate the changes in temporal relationships between activity cycles and environmental cycles (Daan & Aschoff 1975). The timings of onset and end of activity can be easily used as reference points for rhythms (Chandrashekharan et al 1993). The phase relationships between two oscillations, one entering as the other exits is determined by the ratio of their frequencies (Aschoff and Wever 1962). The circadian role states that light active organisms increase or shorten the circadian frequency, whereas dark active organisms lengthen the period with increasing intensity. The behaviour of birds entering and leaving communal roosts depends on number of individuals involved and in timing of their movements according to relation of the time of the year, light intensity and weather. Study of entry and exit behaviour could help how strongly their gathering coordinates the activities of birds. Unless they form permanent flocks or engage in pre-roosting assemblage, roost members are more likely to arrive independently and then depart independently (Greig-Smith 1982). Michael & Chao (1973) reported an association between roosting behaviour, time of sunset and light intensity. The birds arriving after sunset directly to the roost and the time of arrival 137 during cloudy days is earlier than on clear days (Bastwade 1976). I found Cattle Egrets that are early settlers devoting more time to encircling than the other species (Table 6.4.) followed by Median egrets. Other species - the Great and the Little Egrets with a lower population are late settlers as they may be maximizing on feeding time in the foraging grounds. These species also spend very little time in fighting but do maintain territoriality by chasing other members from a roost position within the site. The possible benefits from roosting communally are enhanced efficiency in exploiting unevenly distributed food supply. Evidence in support of this hypothesis of food finding by number of breeding colonies has been given by Horn (1968). The birds feed in flocks, roost communally - their main function being to act as information centre where information on location of food within the area served by the roost may be obtained by even the weakest members of the roosting community (Ward 1965, Seigfried 1971b, Zahavi 1971). Patterns of foraging trips of several species of communally roosting birds have been examined earlier so as to know whether the colonies act as information centre to assist the members in finding food (Krebs 1974b, Custer and Osbom 1978, Erwin 1975, Holmes et al. 1979). Communal roosting is advantageous for species depending on food that is unevenly distributed and concentrated in areas of temporary abundance. Individuals who have difficulty in locating sites thus happen to gain in searching time for enhanced feeding success (Ward and Zahavi 1973). During the entire study period duration of total time of emergence (roost break up) in the morning by all the species was found to be shorter than the total time span in settling (assembly) in the evening. This might be due to hunger stimulus in the morning, an internal biological clock mechanism and also social behaviour. The difference 138 observed in the total time span in settling and emerging of the four species could be related to the distance of their dispersion to various feeding areas as well as to the availability of the amount of food in the surrounding area. A detailed study on these aspects is needed to formulate strategies on communal roosting of egrets. Another interesting finding of this study is that during the winters when day length is shorter the egrets emerged early from the roost site and arrived late. Contrary to this in summers when day length is longer they departed late and arrived early at the roost. This may be for attaining enhanced feeding efficiency during a short day in the winters. In the present study I did not find differences in roost site characteristics amongst egrets, as there may be less competifion for roosting space within the site. There may be several other causes of this absence of competition amongst coexisting egrets. Firstly, it may be due to low population (Table 6.10) in the study area where the largest flock size at the roosting site was never more than 500. At an area where the population size is higher and the competition is stiff for space at the roost site, some partitioning mechanism amongst the sympatric species might be operative. Second, though roosting is an important activity for the egrets, measures of resource partifioning on the basis of roosting pattern, foraging, general activity budget and spatio-temporal distribution may be adequate for ecological isolation. However, further studies including nightlong observation may unfurl more facts about microhabitat features of the roost site and their association with the birds. 139 0) u v^^rl-r--OVO'-^OOO^r^O^O c CD DC H CTi I— o ^ 'O rn ON T-^ o '^ in 00 4-> o fNI T3 C CU fO 00 t~~- Vi :Z o\ o^ Zl ON =» Z^ 2 ra H 4->^ _i 10 fD o JZ oL- j)<: in (N O (N (N r<-) ^ in (J) '^ m O (N ^ ^ »sO 'O ^ in in in in VO in ^ NO E •4-1 o ro vt 1/1 -M <»*-N 0) fc ON 0) ON NO (N r~- ^^ in m t-^ in 00 o t^ NO NO r^ r~- 00 NO r- NO r-- t~- r^ V4— u H 0) O bc H E lO U-J cu 0) (U 'u u c cu NO 00 ON (N m in 00 oo a. H rsi in o 0) to U p en NO NO in in in in in in in in NO NO 0) £ -4—> (U Q. E m iri m ^ IT) O) vo vo m C/5 H H B 2 tn NO NO iri CM o H (N in in 00 00 00 ON ON ON ON 00 00 t- y^ (Z5 oo r-~ t: C ro n U) ^ 11 o NOinm>ninNommNO E o H 4-1 rs1l "m ^-1 •M O o -M o NO r- 00 o in Ti- o in CO •o '--^ H o r^ 00 oo 00 00 ON ON ON ON oo oo r- c QJ C/3 r^ rtj JK^ m /—s _i t?; '^-^^ "* ON r—t m in o in 1—1 (N in rt in (1) 4-> H fO O) 4> 1/1 r 4-> ON ON m 00 en 00 ON tJ 1_ C8 H in •5- in o O) m OO ^ lO 0) u CZ3 00 00 00 ON ON ON ON 00 OO 00 ^ >*- 0) o F w 4-> 0) •4-> () Q. s If) in (N 00 in o in vo •sO c in m o CO rn 3 U U) k_ i> 00 00 00 ON ON ON ON 00 00 r- r- •i-J (- ra G m Q. s ^ k. to fN ;4 «o U 1) X) -O XI V C3 B 3 a l-H (U o > e x> O c s 53 ^ a OH (0 3 "3 3 o o O H < GO o z Q rtJ I/) •4-> OJ k_ 01 CD 0 0 0 0 0 0 in 0 0 in in 0 IT) in in (/I r^ (N ^ 0 0 0 0 ^ »—H (N (N m ^H "u O) Q. to u Q. I9£ u 0 0 0 0 0 0 0 0 0 0 0 0 E 9 a (N 0 § O r^ 0 0 (N Tt- M '^ (N -^ '-^ ^ ^ m ::j e a '+* >• 1/o1 o -4-> u c U m U O 0 0 in ro 0 in 0 0 in in 0 0 o W ro ro 0 0 ro in (N in ro 0 ro (N 0 0 0 •^ (N CT <4-i5> C c 4-> u o OJ o Q. 1- S • « 1 o Tt •)-> O u5 a. CiO Of V OB £3 tJ) • 1—( o A a '55 10 a > 1- o O 13 op X u U U E ffio C31 "(U X •M in m r-- cu bX) 00 ^ »ri (N "^ -H •M o -H -H ro o in r- oo x: rsi r^ r--^ iri t 1 1-1 b o O o SMMTfM / 4> in -^d OJ JS UD ••- U • PN ro 1/3 a> m Tt- OS _j u Tt- ro tf3 Ml ON ^ 00 rj r-^ ^ ro "« 1^ (N CO s a -H -H -H •B -H • p^ « (N ON t! 'cu Tf ro (U JZ • mm 00 > nsV MD • »K S •o ro «M OJ (/J O 4-1 -M k< xz 4— s -^d s (N ON 1_ ON OO T3 ZJ 'I- en _C bX) >4o— r-^ ^ od V4— •4-> ON O to 4> -H -H ^ o 4^ L. CT> '^ in ON 0) c ON in X3 o (N (N E E o 3 ro C en .^ c ro '•4-> •4-> to o o I4_ o O L^. c o < ro k£i a; ^^ Z X CQ o lis c:? ^ VO O >HJ <: ^ OJ in o H « 1 1 X) A (N in < Ho re 1- Ol •(1) ^ /^^ k_ rt j5 o 3 o fN Tf ON o u m VO o 1 Tf "—; (N o '^ t r<^ fD 1—1 -H -H -H -H Q. o (N -H oo oo 00 tu o oo fM ^ 'O -^ V4— o 00 T3 •3 ^ oo m e s Ol 0) «• PMM V4— o •(/) O L. V (U .c 'u u 3s *- CL S rj- r^ m ^^ to rn o ^ ^ y « r<-i (N o r<-i O •i-> -H -H in •4-> a> -w +1 V4— fD ^ '^ (N IT) O CL t~^ vd -^ T—< W E e rtJ 3 1>0^ 44 T3 1_ 3 •> O TD >i— _C •!-> fN U 0) a> 03 u Tt- '—' 00 m tro _l I5X) o o in o in CL U o -H ro o o -H -^d M ro sz in o iri I/-) in o 0) O) S -H B +1 -H w (J "? -H IT) -a 0) •3 -a O) D. iri •»-> 1/5 ^ vo ON §.^ © V) -M u '^ S. E Q. l^ I/) 1- e o u to in ^£ o o iri -H <*= V) -H -H -H O 05 o m m m 0\ IT) M3 11 s ^ Tf •g fo •> oi •o .g — V) V4- O 00 00 o o in o in OJ DX) o in E O) 4> -H -H -H CO -H c 1_ m ^ D <9 TH 75 (/) jO u u >^ Q. O c C ^-> 03 ^ cu U O 0) u- O Z O CN do OH o oCl , a O c vo © C s a o « o U ki < (U T3 o o I- CI, D n3 cu 00 I. O bX) ON 1—1 NO I/) *~^ 1—'i t-; •O -H -H -H +1 in -H -H 'u ON (U Q. (N ^' ri-i V) a CNl u Q. E .A >^ .2f ON 00 r-- o 3 "3 oi .p s -H -H -H -H -H -H s ON NO 00 •3 O^ '> ON ON T3 ,B sd ^ s (U ^ 1_ o 0) o 00 fM o > 1—1 00 o 1 '^ CO !>; 1 o in o u 1—1 T—H ON (N (N 00 c o -H -H -H -H -n o o ON en '•4-> fN ON 00 rD ***-^ ^ NO •-^ 4-> CU 0) a; ra rT) > fU •o JC c ^ 2 u CO (J > o aa u < o> S vd O in S .T3 ° V o O in I in < A O m o C/3 f= I in A H Hre + r^ (N o H u a •** a « 1^ a 00 o o fSI "S oS o w o 9t rsi 6 e ^ :£ s ?s C8 _j (0 01 U •(D 3 fN (N N « I 4-1 a r^ U o Q O) C o bX) 0) c u « (N ^ ^ CD Q. < ON (N u •»_ 4-1 Q. ii E u ^ ^ ON O 1_ q D .a a -H -H -H -H £ ^ r^ cu r<-i o S ON I/) « ON ON •l-J q c I. q q ON •4—» 3 -H -H -H o < -n ON u lA -4-1 i/3 rn •^ (N '—' c o o O '^ o (S oUi ON ON 00 00 c/2 CO ON QJ Xi DO -4—' 1) lA C/5 C/5 t>i kH c« (U O _c -4—* .a t>0 o (U 00 XI ;-! i-i La W w o W 00 00 a M W 11/3) 'in !Z5 > 1) m -t—» i T3 •a 'B a. O 4—' (U oo I- o O o < Q u J s w J B in >n in in in in o o o o o o o o o o o o —) C V V V V V V •i-« la 00 (N in "(U rn (N CN (N o CO o ^ II 11 II II II II d 4-1 H N N N N N N I/) 1c- (U B in in in in in o o o o o o (U ti o o o o o o •4-» 03 V V V V V V CJ Q. a. a. PL, V •5? Ol a I oo" ;-< c o ON o '•4-o> ON o o ^H (N (N (N .— (N 00 o B in 1- o W H N N N N N N cn A c a N DC T3 ,B -a o o O o o o :» o o o o o o o s V V V V V V CD o '••iJ in k. PH PH PH OH PH PH (/> B B 00 O (N ON o u O o O B 00 00 00 00 00 00 00 E V N c II II II II II II 2 s N N N N N N £ * * * * * * •3 4-> V) cn ;. o o o o o o c 3 o o o o o o o o E O V V V V V V O PH OH PH OH ro rsi a. c in ON rn ON" g _B MS »n '•4-' '-C T3 te (U ro o O 4—» ^c o O II II II II II II N N N N N N * * * * * * Si c -4—' ro .n. (U ON ON in 00 ON XJ o O ON ^ \o O o a^ m (N \D H" II c N N N OH '•4-> N N N 10 o 1o_ 14— en o o o cu (/I D iri ^^ ^ VO ro >o o r~- »—( O (N o a» B •I ^ r~- m m ^ r-- c 00 T3 N in k_ N N N N N (N ro en S A 0) B 1- N T3 Ul 00 -i-i o in o (U I 00 ON 1- u o r~- CO CT ^^ a in^ 0) ^ V H' (4— O u o N N N N N N o O O B O rsi u W , OH Q; 1 •<—• 44 u TH CO (U O s W Q.O o w rsl o ON r- o ••-» o 00 U-) TT o o _y OJ o ON TT r- o 00 O •4-> ^ k. a N N N N N D a 6.2- a D 6.0- 5.8- 5.6. • n 5.4. a D • 5.2. o i »- 111 5.0 1 —1 5.0 55 6.0 6.5 7.0 7.5 SRT Figure 6.1b: Correlation between sunrise time (SRT) and monthly mean emergence time of Little Egrets (ETLE) communally roosting at Sheikha Lake b.e- D % 6.4- a 6-2- D • D 6.0- 5.8- 5.6- o 5.4 D UJ _l uJ 5.2 —1 5.0 5.5 6.0 6.5 7.0 7.5 SRT Figure 6.1c: Correlation between sunrise time (SRT) and monthly mean emergence time of Median Egrets (ETME) communally roosting at Sheikha Lake % 0 6.0- 5.8- 5.6- D 5.4- D n • D 5.2- 0 B 5.0- 4.8- UJ 4 6- • UJ 44 1 5.0 5.5 6.0 6.5 7.0 7.5 SRT Figure 6.1d: Correlation between sunrise time (SRT) and monthly mean emergence time of Great Egrets (ETGE) communally roosting at Sheikha Lake UJ O UJ 50 Figure 6.2a: Correlation between sunset time (SST) and montlily mean settling time of Cattle Egrets (STCE) communally roosting at Sheikha Lake. 19.5 19.0 18.5- 18.0 LU O W 17.5 Figure 6.2b: Correlation between sunset time (SST) and monthly mean settling time of Little Egrets (STLE) communally roosting at Sheikha Lake. I3.0- a 19.0 18.5- a iP D D D 18.0- 17.5. D • UJ _J 1- 17.0 (0 T 1 17.0 17 5 18.0 18.5 19.0 19.5 SST Figure 6.2c: Correlation between sunset time (SST) and monthly mean settling time of Median Egrets (STME) communally roosting at Sheikha Lake. 19.5 19.0- 18.5 18.0 17.5 III CO 17.0 19,5 Figure 6.2d: Correlation between sunset time (SST) and monthly mean settling time of Great Egrets (STGE) communally roosting at Sheikha Lake 20.0 19.5 19.0 18.5 18.0 111 (0 17 5 19.5 Figure 6.3 a: Correlation between the monthly mean day length (MDL) and total roosting hours (MTRH) of Cattle Egrets communally roosting at Sheikha Lake 14.0 13.5 13.0 12.5- 12.0- 11.5 11.0 10.5 10.0 MTRH Figure 6.3 b: Correlation between the monthly mean day length (MDL) and total roosting hours (MTRH) of Little Egrets communally roosting at Sheikha Lake 14.U- 0 13.5- D D 13.0- On 12.5- 12.0- 11.5- a D D 11.0- 10.5- D Q 10.0 1 1 1 —» 10 11 12 13 14 15 MTRH Figure 6.3 c: Correlation between the monthly mean day length (MDL) and total roosting hours (MTRH) of Median Egrets communally roostino at Sheikha Lake 14.0 Figure 6.3 d: Correlation between the monthly mean day length (MDL) and total roosting hours (MTRH) of Great Egrets communally roostino at Sheikha L3kfi 14.0 13.5 13.0- 12.5 12.0 11.5- 11.0 10.5 10.0 SUMMARY AND RECOMMENDATIONS This work was an attempt to obtaining a partial answer to an elementary question about niche space. Using the coexistence of four sympatric egrets as a tool it has probed into the question that what is the minimum dimension of a niche space necessary to represent the overlaps among observed niches. It provided an opportunity to synthesize theory and observation. However, each attempt at a synthesis rose some probing too. 1 therefore, propose some aspects to be looked upon for future ecological research in the area of species coexistence and conservation measures for wading birds with special reference to sympatric egrets. Future research directions As study of demography of any species is important for identifying the factors governing population regulation therefore, a long-term study of marked populations of egrets is essential for their conservation. My findings on the spatial segregation of four sympatric egrets suggest that they differentiate in foraging niches. Coexisting species significantly associate themselves to different micro-habitat types and habitat variables. Though a little overlap was also observed, this mechanism helps to reduce competition for foraging space. The same trend was observed in their associations with other waterfowl using the wetland as a foraging habitat. For instance egrets frequenting the wetland during winters declines as the teaming winter visitors outnumber them. Yet if inter-specific competition was the primary mechanism underlying coexistence and roosting space was a limiting factor, then all roosting habitats would have been either occupied by one species or there would have been distinct niches within the roost site for different species. Instead it was found that utilized roost site variables were the same for the four species in the study area. However, spatial segregation in 158 roosting activity was observed with respect to roosting patterns such as time of arrival and emergence and total roosting hours. In the present study resource partitioning amongst the four sympatric species of egrets was inferred based on the food selection and foraging ecology. Corresponding to their eco-morphology and habitat affiliations different species were found associated with different food items and size of the prey. Differential use of the foraging behaviours was also observed. Natural selection might have operated on the evolution of specialized prey catching techniques in these species. There was considerable overlap in foraging variables amongst the species but never a complete overlap. The degree of overlap depends on availability of food and foraging habitat as well as competition from conspecifics and sympatric individuals. Treating time as an important resource, the four sympatric species of egrets in this study also showed temporal variations. This was manifested in the time and activity budgets adapted by different species to avoid competition. These activity patterns were adjusted according to temporal variables of changing seasons and daily cycles. The innate opportunism and adaptation to environmental gradients may be the factors behind this arrangement. Conservation implications Conserving egrets and managing their habitats has received little attention in India as compared to wide spread concern for wading birds that contributed to founding the Modem Conservation Movement in America (Sprunt et al. 1978). To ensure such protection to egrets in India development of a large body of basic and applied research, population monitoring, directed management action, indirect conservation through 159 wetland habitat protection, manipulation and restoration and the emergence of a professional society of specialists devoted to their welfare is needed (Kushlan 1997). The Ramsar convention and the International Waterfowl Census have contributed significantly in increasing knowledge on the status of waterfowls vis a vis the egrets. Individual species census such as the collaborative censuses of grey herons Ardea cineria in England could serve as models for future. Egrets for the most part depend on wetlands - so do a large portion of the world's human population, which are under increasing pressure worldwide. As the values and functions of wetlands have become better understood so has appreciation for the place of egrets within these ecosystems. Research on wading birds suggests the conservation of wetlands in the light of the following aspects. Colony site requirements: Colony of wading birds face particular biological and management problems. In contrast to the solitary breeders the loss of a single breeding site can result in the loss of a whole population segment. Nests of herons and egrets are recorded at variable heights from ground. Though some species are characterized by high plasticity the great egret and the little egret have much more specific requirements. For heronries there should be a security zone. In most situations the security zone is either provided by water or dense undergrowth as barrier for predators. In the absence of all this the birds will establish only if the vegetation allows them to nest at a certain height. In addition to these the size structure, shape, orientation of the nest site and availability of nest building material is also important. As suggested by (Subramanya 1996) some possible measures to bring more heronries under state protection could be to ensure 160 ensure future availability of roosting and nesting sites, creating heronries at natural potential sites and creation of large waterbodies. Feeding site requirements. In contrast to the nest site characteristics the size and quality of feeding areas required to sustain breeding populations of a particular size are still poorly understood. Studies on feeding ecology are difficult and generally involve considerable costs of manpower and material. Area and quality of fresh water habitat, diversity of feeding patches, flight distances and ability to maintain periodicity in a species are important factors to sustain the waterfowl population. We need information on bottleneck areas and periods. This is a field of investigation, which could provide the key to many questions. Habitat destruction is one of the most important factors responsible for the depletion of a species. The forest department should help prevent on going poaching and protect breeding colonies during the nesting. Reed removal and overexploitation of the open water for cultivation of water-chestnut may rob the egrets of potential feeding grounds. If unabated, fishing in the Lake and the Canal will also deplete the food availability to the egrets and cormorants. Paddy fields are one of the most important habitats of the egrets where they are found feeding in large numbers. Therefore, selective use of harmless pesficides should be launched. Changing agricultural pracfices that promote the use of harmful contaminants may become a serious threat in future. Water conservation should be given priority and alternative habitat should be made available so that in adverse conditions breeding and sustenance of the birds is not affected. Ensuring water during the summer season is also recommended so that food supply to breeding birds is ensured in the Lake. 161 In India community based conservation helps significantly in protection and management of biodiversity (Khan & Abbasi 2001). Strict protection of bird colonies is afforded by Luna Villagers, in Kutch, Gujarat (Tiwari & Rahmani 1998). Similarly local community of the Sheikha Lake also subscribes to the tradition of providing protection to the Lake and its biodiversity. Specially, when the egrets and other wading birds select a village woodlot or some trees within the precincts of the human habitation protection is accorded to them from threats of egg and sub-adult collection and hunting for food. But old traditions are fading and unless support is provided for their revival, situation at the Sheikha Lake too might worsen. At some other places in India cattle egrets are facing threats of hunting because their dried and powdered liver is used for medicines (Bharos 1998). Erwin (1989) has shown wading birds having maximum tolerance to human intrusion in terms of flushing distance amongst all colonial nesters. In certain cases the villagers have even replaced chicks accidentally fallen from the nests. Such practices should be abetted and revived where they are debilitating. Long-term research and monitoring of programs as the active habitat management and restoration undertaken in Italy (Fasola & Ghidini 1983) and France (Hafner et al. 1994) may be considered in India also to evaluate the past conservation initiatives, identify pending vulnerability factors and establish future conservation priorities. 162 REFERENCES Abbasi, F., and Yahya, H. S. A., 2003. Waterfowl Conservation Awareness Campaign for Sheikha Jheel, Aligarh, UP, India - an IBA Site. A project Report: DWS, BNHS, RSPB, BLI Abdulali H., 1949. Mergansers fishing. J5Af//548(3):585-586. Abdulali H., 1965.Notes on Indian Birds 7 - on the size of the white egrets in India. {Egretta alba, intermedia andgarzetta) JBNHS 62(3):521 -528. Abdulali H., 1967. Unusual method of fishing by little egret Egretta garzetta Linnaeus. y5iV//S64(3):557-558. Abdulali H., 1968. A catalogue of the birds in the collection of the Bombay Natural History Society. Gaviiformes to Ciconiiformesy57V/f5'65(1): 182-199. Abrams, P., 1986. The competitive exclusion principle: other views. Trends Ecol Evol 1:131- 132. Anon. 1921. Egret farming in Sind. JBNHS 27(4y.944-947. Anon. 1976. Indian Daily Weather Report for the years 1974 and 1975. Indian Meteorological Department, New Delhi. Altmann, J., 1973. Observational Study of behavior: Sampling methods. Behaviour XLIX:227-267. Ali, S., 1996. The Book of Indian Birds Salim Ali Centenary Edition, Bombay Natural History Society, Oxford University Press. Bombay Ali, S., and Ripley, S. D., 1968. Handbook of the Birds of India and Pakistan. Oxford University Press. London New York Amat, J. A., 1984. Ecological segregation between red-crested pochard Netta rufina and pochard Aythyaferina in a fluctuating environment. Ardea 72:229 - 233. Alonso, J. S., Alonso, J. A., and Veiga, J.P., 1987. Flocking in wintering Common Cranes: influence of population size, food abundance and habitat patchiness. Ornis scand. 18: 53-60 *Aschoff, J. and Wever, R., 1962. Uber phasenbezienhugen zwischen biologischer Tagesperiodik und Zeitgeberperiodik. Z Vergl. Physiol. 46:115-128pp. Aschoff, J. 1965. The phase angle difference in circadian periodicity. In: Circadian clocks, i. Aschoff (ed.), (Amsterdam: North Holland) 262- 267p. 163 Aschoff, J., Dann, S., and Honma, K.I., 1982. Zeitgebers, entrainment and Masking: Some unsettled questions; In: Vertebrate circadian rhythms i. Aschoff, S. Dann and G.A. Gross (eds.), (Berlin, Heidelberg: Springer Verlag) pp 13-24. Atkinson, E., 1875. Statistical, Descriptive and Historical account of the N.W.P. of India II. (Meerut Division) Part I, District Gazetteers, Govt, of India Bahadur, P., 1976. Technical Feasibility of Groundwater on Compact Area Basis. District Aligarh and Roorkee Division. Govt, of Uttar Pradesh Baldassarre, G. A., and Bolen, E. G., 1994. Waterfowl Ecology and Management. John Wiley and Sons. Inc. New York pp 224 -281. Baker, M. C, and Baker A. E. M., 1973. Niche relationships among six species of shore birds on their wintering and breeding ranges. Ecological Monograpphs 43:193-212. Bardsley, L., and Beebee, T. J. C, 1998. Interspecific competition between Bufo larvae under conditions of community transition. Ecology 79:1751-1759. Barnard, C.J., 1980. Equilibrium flock size and factors affecting arrival and departure in feeding house Sparrows. Anim. Behav. 28:503-511. Barnard, C.J., and Thompson, D. B. A., 1985. Gulls and Plovers: Ecology and behaviour of mixed species feeding groups. Columbia Univ. Press, New York. Bastawde, D.B., 1976. The roosting habits of Green Bee-Eater. J. Bom.. Nat. Hist. Soc. 73 (1): 215-222. Bayer, R. D., 1981. Arrival and departure frequencies of great Blue Herons at two Oregon Estuarine colonies. The Auk 98:589-595. Bayer, R.D., 1982. How important are colonies as information Centres? y4w/t 99:31-40. Bayer, R.D., 1985. Bill lengths of Herons and Egrets as an estimator of prey size. Colonial Waterbirds 8(2): 104-109 Beckerman, A.P., 2000. Counterintuitive outcomes of inter specific competition between two grasshopper species along the source gradient. Ecology 81:948-957. Begon, M., Harper J. L., and Townsend C. R., 1990. Ecology: Individuals, Populations and Communities. Blackwell Scientific Publications. Belovsky, G. E., 1984. Moose and snowshoe hare competition and a mechanistic explanation from foraging theory. Oecologia 61: 150-159. 164 Benoit, R., Dasgranges, J. L. and McNeil, R., 1993. Directions of arrivals of Great Blue Herons at nests with large chicks near Montreal, Quebec. Can. J. Zool. 71:2250- 2257. Benson, C.E., 1922. Egret farming in Sind. J5Af//528(3):748-750. Bethke, R. W., 1991. Seasonality and waterfowl competitions in waterfowl guilds - a comment. Ecology 72: 1155-1158. Betts, B. J., & Jenni, D. A., 1991. Time Budgets and the adaptiveness of polyandry in Northern Jacanas. Wilson Bulletin 103(4): 578 - 597. *Beaubaton, D., 1985. Motor plans and programs in a goal-directed behaviour: reaching to grasp an object. Proceedings of the 19''' International Ethological Conference, 3:209- 217. Toulouse, France: Universite Paul Sabatiere Beidenweg, D. W., 1983. Time and energy budgets of the mocking bird Mimus polyglottus during the breeding season. Auk 100:149 - 160. Bennett, W. A., 1990. Scale of investigations and the detection of competition: an example from the house sparrow and the house finch introductions in North America . Am Nat. 135:725-747. Benvenuti, S., Antonia, L. D., and Lyngs P., 2001. Foraging behaviour and time allocation of chick-rearing Razorbills ^/ca torda at Grassholmen, Central Baltic Sea. Ibis 143:402 -412 Bhargava, R.N., Singh, Y.D., & Bohra, P., 1982. Some observations on the nesting of cattle egrets Bubulcus ibis in the Zoological Garden, Jodhpur. Pavo 20:44-45. Bharos, A. M. K., 1998. Use of cattle egret Bubulcus ibis organs as medicine. J. Bom. Nat. Hist. Soc. 95(3):503. Bhupathy, S., 1995. Ecology of Purple Moorhen Porphyrio porphyrio from January to March 1985. in Keoladeo National Park, Bharatpur, M.Sc. Dissertation, Bharthidasan University, Tiruchirapalli, Tamil Nadu, India. Birch, G., 1914. Egret farming in Smd JBNHS 13(1): 184 BirdLife International 2000. Threatened birds of the world. Barcelona and Cambridge, UK, Lynx Edicions and BirdLife International. Bildstein, L. K., 1977. Wading bird science: A guide for the twenty first century. Colonial Waterbirds 20il):U8-\42. Boettcher, R. and Haig, S. M., 1994. Behavioural pattern and nearest neighbour distance among non-breeding American Avocets. Condor 96:973 - 986. 165 Bosakowski, T. 1989. Observations on the evening departure and activity of wintering shorteared owls in New Jersey. J. Raptor Res 23:162 - 166. Bowers, M. A, and Dooley, J. L., 1991. Landscape composition and the intensity and outcome of two species competition. Oikos 60:180-186. Brady, J., 1982. Circadian rhythm in animal physiology. In: Biological Time Keeping, (ed.) John Brady. Society for Experimental Biology, Seminar Series 14, Cambridge University Press Cambridge, pp 121 - 142. Bremmer, F. J., 1965. Metabolism and survival times of Starlings at various temperatures. Wilson Bull. 11 •M^-Z95. Brewer, R., 1988.r/?e Science of Ecology. Saunders College Publishing. Brock, S. E. 1914. Ecological relations of bird distribution. Brit. Birds. 8:29-44. Brown, J. S., 1989. Coexistence on a seasonal resource. Am Nat 133: 168-182. Bunning, E., 1973. Physiological Clock (Revised 3'^'' edition) Springer Verlag, Berlin, Heidelberg, New York. Bunning, E., 1982. Mechanisms of circadian rhythms in plant cells. In: Cellular Pacemakers D. Carperator (Ed.). John Wiley, New York, London Sydney. Vol.2. pp 174-198. Burg, C.G., Beehler B.M., & Ripley S.D., 1994. Ornithology of the Indian Subcontinent 1872 - 1992. Burger A. E., and Piatt J. F., 1970. Flexible time budgets in common murres: buffers against variable prey abundance. Stud avian Biol. 14:71-83. Burton, B. A., and Hudson, J. R., 1978. Activity budgets of lesser snow geese wintering on the Eraser River Estuary, British Columbia Wildfowl 29:111 - 117. Bustnes, J. O., and Lonne O. J., 1997. Habitat partitioning among sympatric wintering common eiders Somateria mollissima and king eiders 5*. spectabilis. Ibis 139:549- 544. Caccamaise, D. F., and Morrison, D. W., 1986. Avian communal roosting: implications of diurnal activity centres, ^w. Nat. 128:191-198. Caccamaise, D. F. and Morrison, D. W., 1988. Avian communal roosting: A test of the patch sitting hypothesis. Condor 90:453-458. Cairns, D. K., 1987. Seabirds as monitors of marine food supply. Biol. Oceanogr. 5:261-271. 166 Causten, D. R., 1988. An Introduction to Vegetation Analysis: Principles, Practices and Interpretation. Unwin Hyman, London. Caldwell, G. S., 1979. Social dynamics of foraging herons and egrets in tropical mixed- species flocks. Ph.D. diss. Berkley, University of California, California: Campos, F., and Lekuona, J. M., 1997. Temporal variations in the feeding habits of the purple heron Ardeapurpurea during the breeding season. Ibis 139: 447 - 451. Cameron, G. N., 1971. Niche overlap and competition in woodrats. J. Mammals 52: 288 - 296. Cody, M. L., 1968. On the methods of resource division in the grassland bird communities. Am. Nat. 102:107-147. Cody, M. L., 1974. Competition and the Structure of Bird Communities. Princeton University Press, Princeton, New Jersey. Cody, M. L., 1975. Towards a theory of continental species diversities In: Ecology and Evolution of Communities M. L. Cody and J. M. Diamond (eds) Belknap, Cambridge, Massachussets. Pp 214-257. Cody, M. L., 1985. An introduction to habitat selection in birds. In: Habitat Selection in Birds. M. L. Cody (ed..) Academic Press, New York. Pp. 3-56. *Colwell, R. K., and Fuentes, E. R., 1975. Experimental studies of the niche. Annu. Rev. Ecol.Syst. 6:281-310. Connell, J. H., and Orias, E., 1964. The ecological regulation of species diversity. Am. Nat. 98:399-414. Connell, J. H., 1983. On the prevalence and relative importance of interspecific competition: evidence from field experiment. Am Nat 111: 661-696. Cezily, F., Hafner, H., and Boy, V., 1990. Group foraging in little egrets Egretta garzetta: from field evidence to experimental investigation. Behavioural Process, 21: 69-80. Champion, H. G. and Seth, S. K., 1968. A Revised Survey of the Forest Types of India. Govt. of India Press, Nasik. *Chandrashekharan, M. K., Subbaraj R., and Sripathi K., 1993. Reference Phases and circadian rhythm. J. Interdiscipl. Res. 14:43-52. Chen, C, and Hseih, F., 2002. Composition and foraging behaviour of mixed-species flocks led by the grey cheecked fulvetta in Fushan Experimental Forest, Taiwan. Ibis 144:317-330. 167 *Cherel, Y., and Klages, N., 1998. A review of the food of albatrosses. In: Albatross Biology and Conservation G. Robertsen and R. Gales (eds.) Pp.113-136. Chipping Norton, Surrey Beatly & Sons. Christe, P., Richner, H., and Oppliger, A., 1996. Begging, food provisioning and nestling competition in great tits infested with ectoparasites. Behav. Ecol. 7:127-131. Churchill, J. B., Wood, P. B., and Brinker, D., F., 2000. Diurnal roost-site characteristics of Northern saw-whet owls wintering at Assateague Islands, Maryland. Wilson Bull 112 (3):332-336 Colwell, R. K., and Futuyama, D. J., 1971. On the measurement of niche breadth and overlap. Ecology 52:567-576. Counsilman, J. J., 1974, Waking and roosting behaviour of the Indian Myna Emu 74:135- 148. Cruz, A., 1980. Feeding ecology of the black-whiskered vireo and associated gleaning birds in Jamaica. Willson Bull. 92(l):40-52. *Custer, T.W., and Osborn, R. G. 1978. Feeding site description of three heron species near Beaufort North Carolina. In: Wading Birds A. Sprunt IV, J. C. Ogden and S. Winkler (eds.). Natl. Audubon Soc. Res. Rep. No. 7. Natl. Aud. Soc, New York. Pp. 355 - 360. *Curry-Lindahl, K. 1978. Conservation and management of wading birds and their habitats. In: Wading Birds A. Sprunt IV, J. C. Ogden and S. Winkler (eds.). Natl. Audubon Soc. Res. Rep. No. 7. Natl. Aud. Soc, New York. Pp. 355 - 360.New York. Pp. 83 - 98. Daan, S., and Aschoff, J., 1975. Circadian Rhythms of locomotor activity in captive birds and mammals: their variations with seasons and latitudes. Oecologia 18:269-316. Darwin, C, 1859. The Origin of Species. J. M. Dent & Sons Ltd., London, Melbourne Toronto, Everyman's Library. Datta, A., 2001. An ecological study of sympatric Hornbills and fruiting patterns in Tropical Forets in Arunachal Pradesh. Ph.D. Dissertation, Saurashtra University Rajkot. del Hoyo, J., Elliott, A., and Sargatal, J. eds. 1992. Handbook of the Birds of the World Vol. I. Lynx Edicions, Barcelona. *Den Boer, P. J., 1986. The present status of the competitive exclusion principle. Trends Ecol £vo/1:25-28. De Boer W. F., and Prins H. H. T., 1990. Large herbivores that strive mightily but eat and drink as friends.Oecologia 82:264-274. 168 Delaney, D. K., Grubb T. G., Beier, P., 1999. Activity patterns of nesting Mexican Spotted owls The Condor 101:42^9. Diamond, J. M., and Case T. J., 1986. Community Ecology Harper and Row, New York. Dimalexis, A., Pyrovetsi M., and Sgardelis S., 1997. Foraging ecology of the grey heron Ardea cineria, Great Egret Ardea alba and Little Egret Egretta garzetta in response to habitat at two greek wetlands, Colonial Waterbirds 20(2): 261-272. Dow, D. D., 1979. Agonistic and spacing behaviour of the noisy miner Manorina melanocephala, a communally breeding honey eater. Ibis 121(4): 423-426. Draulans, D., and van Vessem, J., 1986. Communal roosting in Grey Herons (Ardea cineria) in Belgium. Colonial Waterbirds 9:18-24. Draulans D. 1987. Impact of prey density on foraging behaviour of Grey Herons Ardeola greyii. Ardea75:\S9-m. Dubowy, P. J., 1988. Waterfowl communities and seasonal environments: temporal variability in interspecific competition. Ecology 69:1439 - 1453. Dubale, M.S., and Mansuri A.P., 1973. The role of mechanical advantage and ligaments in the feeding apparatus of some Indian Ardeid birds. Pavo 11:71-84 Dubale, M.S., and Mansuri A.P., 1974. The qualitative differences in jaw muscles in relation to feeding behaviour of certain Indian herons and egrets I - Adductors of the lower jaw, abductors of the lower jaw and retractors of the upper jaw. Pavol2:3Q-45. Dubale, M.S., and Mansuri A.P., 1974a. The qualitative differences in jaw muscles in relation to feeding behaviour of certain Indian herons and egrets I -Retractors of the upper jaw and adductors of the lower jaw, abductor of the lower jaw and protractors of the upper jaw.Povo 12:46 - 57. Dubale, M.S., and Mansuri A.P., 1977. Heterogeneity in fiber types and metabolic adaptations in the jaw muscles of some Indian Ardeid birds. Pavo 15: 73-81 Dudgeon, S. R., Steneck R. S., Davison, 1. R., and Vadas R. L., 1999. Coexistence of similar species in a space limited intertidal zone. Ecological Monograph 69:331-352 Dugan P., Hafner H., and Boy V., 1993. Habitat switches and foraging success in the little egret Egretta garzetta. Proc. Of the IOC, 19:1868-1877. Eberhardt L. E., Books, G. G., Anthony, R. G., and Rickard W. H., 1989. Activity budgets of Canada Geese during brood rearing. Auk 106:218 - 224. 169 Eguchi, K., 1988. Ecological significance of the time budgets of the Brown dipper. Cinclus pallasi (Temminck) Ecology 38:243 - 225. Elmberg, J., Poysa, H., Sjoberg, K., Nummi, P., 1997. Interspecific interactions and co existence in dabbling ducks: observations and an experiment. Oecologia 111:129- 136. Elton, C. S., 1927. Animal Ecology. Sidgwick, and Jackson, London. Erkinaro, E., 1972. Precision of the circadian clock in Tengmalms' owl Aegolius funereus L. during various seasons. Aquillo (oulu) 13:48 - 52. Erwin, R. M., 1975. Foraging decisions, patch use and seasonality in egrets (Aves: Ciconiiformes). Ecology 66(3): 837 - 844 Erwin, R. M., Hanfer H. & Dugan P. J. 1985. Difference in the feeding behavior of Little Egrets in two habitats in the Camargue ,France. Wilson Bulletin 97: 534 - 538. Erwin, R.M., 1989. Responses to human intruders by birds nesting in colonies: Experimental results and management guidelines. Colonial Waterbirds 12(1): 104 -108. Ettinger, A. O., and King, J. R., 1980. Time and energy budget of the willow flycatcher Empidonox trailli during the breeding season. Auk 97: 533 - 546. Fasola ,M. and M.Ghidini. 1983. Use of feeding habitat by breeding Night Heron and Little Egret. Avocetta 7:29-36. Fasola, M., 1994. Opportunistic use of foraging resources by heron communities in southern Europe. Ecography 17: 113 - 123. Fasola, M., Hafner H., Kayser Y., Bennetts E., and Cezily F., 2002. Individual dispersal among colonies of Little Egrets Egretta garzetta Ibis 144: 192-199. Flemming, T. H., 1981. Winter roosting and feeding behaviour of pied wagtails near Oxford, England. Ibis n:i-Ae3-A16. Folk, C, 1971. Astudy on diurnal activity rhythms and feeding habits of Aythya juligula. Acta Sc. Nat. Brno. 23(1): 45 - 54. Forbes, L.S., 1989. Coloniality in Herons: Lack's Predation Hypothesis reconsidered. Colonial Waterbirds 12(1): 24 - 29. Fowler, J., and Cohen, L., 1986. Statistics for Ornithologists. BTO Guide No. 2 British Trust for Ornithology, UK. Francis, W. J., 1976. Micrometeorology of a blackbird roost. J. Wildl. Manage. 40:132-136. 170 Frederickson, L. H., and Drobney, D. R., 1979. Habitat utilization by post breeding waterfowls. Pages. 119 - 131 In. (ed.) T. A. Bookhout, Waterfowl and Wetlands - an integrated review. Nortcent Sect. The Wildl. Soc, Madison, Wis. Fuller, M. R., 1979. Spatiotemporal Ecology of four sympatric raptor species. Ph. D. Dissertation, Univ. Minnesota, Minneapolis, MN. Furness, R. W., and Barrett R. T., 1985. The food requirement and ecological relationships of a seabird community in North Norway. Ornis Scand. 16: 305-313 Gadgil, M., 1972. The function of communal roosts; relevance of mixed roosts. Ibis 114:531- 533. Gadgil, M., & Ali S., 1975. Communal roosting habits of Indian birds. J. Bom. Nat. Hist. Soc. 72(3):716-727. Gassett, J. W., Folk, T. H., Alexy K. J., Miller K. V, Champion, B. R., Boyd F. L., and Hall D. I., 2000. Food habits of cattle egrets on St. Croix, US Virgin Islands. Willson Bull 112(2):268-271. Cause G. F., 1934. The Struggle for existence. Hafner, New York. Gauthier, G., Bedard, J., and Bedard, Y., 1984. Comparison of daily energy expenditure of greater snow geese between two habitats. Can. J. Zool. 62:1304 - 1307. Gilbert, J. J., 1985. Competition between rotifers and Daphnia. Ecology 66:\9A3 -1950. Giller, P. S., 1984. Community Structure and the Niche Chapman and Hall, London. Gilmer, D. S., Kirby, R. E., Ball I. J., and Reich-Mann, J. H., 1977. Postbreeding activities of mallards and wood ducks in North-Central Minnesota. J. Wildl. Manage. 41(3): 345 -359. Gordon, H., Illius A. W., 1989. Resource partitioning by ungulates on the Isle of Rhum Oeco/o^/a 79:383-389. Goudie, R. I., and Ankney, C. D., 1986. Body size, activity budgets and diets of sea ducks wintering in Newfoundland. Ecology. 67(6): 1475 - 1482. Graham, C, 2001. Habitat selection and activity budgets of keel billed toucans at the landscape level. The Condor 103:776 - 784. Grant, P. R., and Grant, B. R., 1980. Annual variation in finch numbers, foraging and food supply on Isla Daphne Major, Galapagos. Oecologia 46: 55 - 62. Greig-Smith, P. W., 1982. Behaviour of birds entering and leaving communal roosts of Madagascar Fodies and Indian Mynas. Ibis 124:529-534. 171 Grinnell, J., 1904. The origin and distribution of the Chestnut-backed Chickadae. Auk 21:364-382. Grinnell, J., 1917. The niche relationships of the California thrasher, yiw^ 34: 427-433. Grinnell, J., 1943. The Philosophy of Nature. Berkeley and Los Angeles, California. Grimmett, R., Inskipp, C, and Inskipp, T., 1998. Birds of the Indian Subcontinent. Oxford University Press, Delhi. Grimmett, R., Inskipp C. & Inskipp T. 2000. Pocket Guide to the Birds of the Indian Subcontinent. Oxfors University Press Grubh, R. B., 1979. Competition and co-existence in Griffon Vultures. J. Bom. Nat. Hist. Soc. 75:810-814 *Gwinner, E., 1966. Periodicity of a circadian rhythms in birds by species specific song cycles (Aves Fringillidae) Carduellis spinus Serinus serinus Experientia 22: 765 - 766. *Gyllin, R., 1967. Dygnstrystm hos korn sparven, Var Faglevarld 26: 19-29. Hafner, H., Boy, V. and Gory, G. 1982. Feeding methods, flock size and feeding success in the little egret Egretta garzetta and the squaco heron Ardeola rulliodes in Camargue, Southern France, Ardea 70: 45 - 54. Hafner, H., Dugan, P. J., and Boy V., 1986. Use of artificial and natural wetlands as feeding sites by Little Egrets egretta garzetta in the Camarge, Southern France. Colonial Waterbirds 9(2): 149-154. Hafner, H., Kayser, Y., and Pineau O., 1994, Ecological determinants of annual fluctuations in numbers of breeding little egrets Egretta garzetta in the Camargue, S. France. Revue Ecologique (Terre et Vie) 49: 33-62. Hafner, H. 1997. Ecology of wading birds. Colonial Waterbirds 20(1): 115 - 120. Hafner, H., and Fasola M., 1997. Long-term monitoring ad conservation of herons and France and Italy. Colonial Waterbirds 20(2): 298 - 305. Hairston, N. G., Smith, F. E., and Slobodkin, F.B., 1960.Community structure, population control, and competition, ^m. Nat. 94:421-425. Hairston, N. G., Sr. 1989. Ecological Experiments, Purpose, Design and Execution. Cambridge University Press, Cambridge. 172 Haley, D. J., and Gjerhshaug J. O., 1997. Inter and Intra-specific dominance relations and feeding behaviour of Golden eagles Aquila chryseatos and Sea eagle Halmetus albicilia at carcasses. Ibis 140: 295 - 301. Hamilton, T. H., 1958. Adapted variations in the genus Vireo. Wilson Bull. 70:307-346. Hamilton, T. H., 1962. Species relationships and adaptations for sympatry in the avian genus Vireo. Condor 64:40-68. Hancock, J. and Kushlan, J., 1984. The Herons Handbook. Croom Helm, London and Sydney Hart, B. L., 1992. Behavioural adaptations to parasites: an ethological approach. J. Parasitol. 78:256-265. Hinde, R. A., 1961. Behaviour. Pp. 373-411 In: Biology and Comparative Physiology of Birds. A. J. Marshall (ed.). Academic press, London, England. Hilaluddin M., Shah JN, & Shawl T. A., 2004. Nest-site selection and breeding success by cattle egrets Bubulcus ibis and Little Egret Egretta garzetta in Amroha, Uttar Pradesh, India. Unpublished, World Pheasant Association, New Delhi, India. Hilden, O., 1965. Habitat selection in birds. Ann. Zool. Fenn. 2:53-75. Hoi, H., and Winkler H, 1994. Predation on nests: a case of apparent competition. Oecologia 98:436-440. Horns, H. S. 1966. Measurements of overlap in comparative ecology studies. Am.Nat. 100(4): 419-424. Holmes, R. T., Black, C. P. and Sherry, T. W., 1979. Comparative population bioenergetics of three insectivores passerines in a deciduous forest. Condor 81:9-20. Horns, C. W., 1983. Foraging ecology of herons in a southern San Francisco Bay salt marsh. Colonial Waterbirds 6: 37 - 44. Hosono, T., 1967. A study of life history of blue magpie (2). Roosting behaviour 1. Misc. Rep. Yamashina Inst. Ornithol. Zool. 5:34-37. Houlihan, P. F., 1986. The Birds of Ancient Egypt and Phillips, Warminster, England. Hudman, S. P., and Chandler, C. R., 2002. Spatial and habitat relationships of redeyed and blue headed vireos in the southern Appalachians. Willson. Bull. 114:(2)227-234. *Hutchinson, G. E., 1957. Concluding Remarks - Cold Springs Harbor. Symp. Quant. Biol. 22:415-427. 173 Hutchinson, G. E., 1959. Homage to Santa Rosalia or why there are so many kinds of animals./^w. Nat. 93:145-159. Huxley, J. S., 1942. Evolution: the Modern Synthesis. London. Ikeda, S., 1956. On the food habits of the Indian Cattle egret Bubulcus ibis coromandus Japanese J. Appl. Zool. 21:83 - 86. Inou Y., 1985. The process of asynchronous hatching and sibling competition in the little egrets Egretta garzetta. Colonial waterbirds 8(1): 1-11. Islam, M. Z., and Rahmani A. R., 2004. Important Bird Areas in India: Priority Sites for Conservtaion. Indian Bird Conservation Network, Bombay Natural History Society and BirldLife International (UK). Pp. xviii + 1133. Jaeger, R. G., 1970a. Competititve exclusion - comments on survival and extinction of species. Bioscience 24: 33 - 39. Jaeger, R. G., 1970b. Potential extinction through competition between two species of terrestrial salamanders. Evolution 24: 632 -642. Jamdar, N., 1984. Unusual plumage in a cattle egret Bubulcus ibis coromandus (Boddaert) JBNHSSl{iyA87. James, R.D., 1976. Foraging behavior and habit selection of three species of vireos in southern Ontario. Wilson Bull.SS:62-75. Jayaraman, S., 1985. Wintering ecology of Coots Fulica atra in Keoladeo National Park, Bharatpur, M.Sc. Dissertation, Bharthidasan University, Tiruchirapalli, Tamil Nadu, India. Jeffries, M. J., and Lawton, J. H., 1984. Enemy free space and the structure of ecological communities. Biol. J. Linn. Soc. 23:269-286. Jenni, D. A. 1969. A study of the ecology of four species of herons during the breeding season at Lake Alice, Alachua County, Florida. Ecol. Monogr.39: 245-270. Joem, A., and Klucas G., 1983. Intra and inter specific competiton in adults of two abundant grasshoppers, from a sandhills grassland. Environ Entomol. 22:352-361. Johnsingh, A. J. T., Paramanadham, K. and Murali S., 1982. Foraging behaviour and interactions of white babblers Turdoides afftnis with other species. J. Bom. Nat. Hist. S'oc. 79(3):503-514. Jha, A., and Sarkar, N. K., 2000. Some observations on the breeding biology of the Cattle egret Bubulcus ibis (Boddaert) The Twilight Vol. 2 Nos. 2 and 3 174 Katzir, G., 1985. Capuring of underwater prey by the Reef Heron Egretta gularis. Proceedings of the 19"' International Ethological Conference, 2: 375. Toulouse, France: Universite Paul Sabatiere Katzner, T. E., Bragin, E. A., Knick, S. T., and Smith, A. T., 2003. Coexistence in a Multispecies assemblage of eagles in central Asia, Condor 105:538-551. Kelt, D.A., Taper, M.L., and Maserve, P.M., 1995. Assessing the impact of competition on community assembly: a case study using small mammals. Ecology76:\283-\296. Kent, D. M., 1986a. Foraging efficiency of sympatric egrets. Colonial Waterbirds 9:81-85. Kent, D. M., 1986b. Behaviour, habitat use and food of three egrets in a marine habitat. Colonial Waterbirds 9:25 - 30. Kersten, M., R. H. Britton, P. J. Dugan and H. Hafner. 1991. Flock feeding intake in Little Egrets: the effects of prey distribution and behavior. Journal of Animal Ecology 60: 241-252. Khan, A. and Abbasi, F., 2001 Community Conserved Areas of UP: an overview with three case studies. Report No.11. Wildlife Society of India & Kalpavriksh. Khan, D. N., 1990. Ecological studies of wetlands around Aligarh city with special reference to Sheikha and Javan, M.Sc. Dissertation, DWS, AMU, Aligarh. Kossenko, S. M., and Fry C. H. 1998. Competition and coexistenc eof the European Bee- eater Merops apiaster and the blu-cheeked Bee-eater M. persicus in Asia. Ibis 140:2- 13. Krebs, J. R., 1974a. Colonial nesting and social feeding as strategies for exploiting food resources in the Great Blue Heron {Ardeola herodias) Behaviour 51:99-134 Krebs, J. R. 1974b. Colonial nesting and social feeding as strategies for exploiting food resources in the Great Blue Heron Behaviour 51:507-530. Krebs, J. R., and Cowie R., 1976. Foraging strategies in birds. Ardea 64: 98 - 115. Krebs, J. R., 1978. Colonial nesting in birds with special reference to Ciconiiformes. National Audubon society Research Report 7: 249 - 297. Krebs J., Houston A., and Chamov. E., 1981. Some recent developments in optimal foraging. In: Forgoing Behaviour: Ecological, Ethological and Psychological Approaches A. Kamil «& T. Sargent (eds.) Graland STPM, New York, USA. Krebs, J. R., and Davies, N. B., 1981. An Introduction to Behavioural Ecology. Blackwell Scientific Publications, Oxford. Krebs C. J., 1989. Ecological Methodology. Harper & Row Publishers, New York 175 Krebs, J. R., Mac Roberts M. H., and Cullen J. M., 1992. Flocking and feeding in the great tit- an experimental study. Ibis 114:507-530. Kushlan, J. A., 1976. Wading bird predation in a seasonally fluctuating pond. Auk 93:464 - 476. Kushlan, J. A., 1978. Feeding behaviour of North American herons. Auk 93: 86 - 74. Kushlan, J. A., 1997. The conservation of wading birds. Colonial Waterbirds 20(1): 115 - 120. Lack, D., \91\. Ecological Isolation in Birds. Blackwell Scientific Publication. Lehner, P.N., 1979. Handbook of Ethological Methods. Garland SFPM Press, New York. Levins, R., 1968. Evolution in Changing Environments. Princeton University Press. Princeton and New Jersey. Lotem, A., Schechtman, E. & Katziri, G. 1991. Capture of submerged prey by little egrets Egretta garzetta: strike depth, strike angle and the problem of light refraction. Anim. Behav 42: 34\-M6. *Lotka, A. J., 1925. Elements of Physical Biology Williams and Wilkins, Baltimore. Lowe-McConnell R. H. 1967. Ecology of the immigrant cattle egret Ardeola ibis in Guyana, South America. Ibis 109: 168-179 MacArthur, R. H., 1958. Population ecology of some warblers of north-eastern coniferous forest. Ecology 39: 599-619. MacArthur, R. H., and Levins R., 1964. Competition, habitat selection and character displacement in patchy environment. Procd Natl Acad Sci USA 51:1207-1210. MacArthur, R. H., and Pianka E. R., 1966. An optimal use of a patchy environment. Am. Nat. 100: 603 - 609. MacArthur, R. H., and Levins, R., 1967. The limiting similarity, convergence and divergence of coexisiting species. Am. Nat. 101: 377-385. MacArthur, R. H., 1972. Geographical Ecology. Harper and Row, New York. Madsen, J., 1985. Habitat selection of farmland feeding geese in West Jutland, Denmark: an example of a niche shift. Ornis Scand 16: 140 - 144. Madsen, J., and Mortensen C. E., 1987. Habitat exploitation and Interspecific competition of moulting geese in East Greenland. Ibis 129: 25 - 44. 176 Mahabal, A., and Bastawade, D. B., 1985. Population ecology and communal roosting behaviour of Pariah Kite Milvus migrans govinda in Pune, Maharashtra. J. BOM. NAT. HIST. SOC. Vol 82 No. 2, pp 337 - 346. Mahabal, A. and Vaidya, V. G., 1989. Diurnal rhythms and seasonal changes in the roosting behaviour of Indian Mynas. Proc. Indian Acad. Sci. (Anim. Sci.) 98(3): 199-209. Maheswaran, G., 1998. Ecology and behaviour of blacknecked stork Ephippiorhynchus asiaticus in Dudwa National Park, Ittar Pradesh, India. Ph.D. Dissertation, Centre of Wildlife nad Ornithology, Aligarh Muslim University, Ailgarh, U. P. India. Marimuthu, G., Rajan, S., and Chandrashekharan, M. K., 1981. Social entrainment of the circadian rhythm in the flight activity of the microcheropteron bat Hipposideros speoris Behav. Ecol. Sociobiol. 8: 147- 150. Marquiss, M, and Duncan K., 194. Diurnal activity patterns of Goosanders Mergus merganser on a Scottish River system. Wildfowl 45: 209 - 221. Marti, C. D., 1974. Feeding activity of four sympatric owls. The Condor 76:45 - 61. Martin, J. L., and Thibault, J. C, 1996. Coexistence in Mediterranean warblers: ecological differences or interspecific territoriality? J. Biogeogr. 23:169-178. May, R., 1973. Stability and Complexity in Model Ecosystems. Princeton University Press, Princeton. May, R. M., 1981. Patterns in multispecies communities. In: Theoretical Ecology, 2"'' Edition R. M. May (ed.), Blackwell Oxford, pp 197-227. May, C. A., & Gutierrez, R. J., 2002. Habitat associations of Mexical spotted Owl nest and roost sites in central Arizona Willson Bull 114(4):457-466. McKnight, S. K., and Hepp, G. R., 1998. Foraging niche-dynamics of Gadwalls and American Coots in winter. The Auk 115(3): 670 - 683. McNeil, R., Benoit R., and Dasgranges J. L., 1993. Day-time and night time activity at a breeding colony of grets blue herons in a nontidal environment. Can. J. Zoo/.71:1075-1078. Menaker, M., and Eskin, A., 1966. Entrainment of circadian rhythms by sound in Passer domesticus. Science 154: 1579- 1581. Metz, K. J., Kent, A. P., and Mallory, M. L., 1991. Do cattle egrets gain information from conspecifics? Oecologia 86: 57 - 61. Meyerriecks, A. J., 1962. Diversity typifies heron feeding. Nat. Hist. N.Y. 71(6): 48 - 59. 177 Michael, E. D., and Chao W. H., 1973. Migration and roosting of chimney swifts in east Texas. .4w^ 90:100-105. Milstein, P., Prestt, I., and Bell, A. A., 1970. The breeding cycle of the grey heron. Ardea 58:171-255. Miller, R. S., 1964. Ecology and distribution of pocket gophers (geomyediae) in Colorado, Ecology 45: 256 - 272. Miller, R. S., 1967. Patterns and processes in competition. Adv ecol. Res. 4: 1 - 74. Miller, R. S., 1968. Conditions of competition between redwings and yellowheaded blackbirds. J. Anim. Ecol. 37: 43 - 62. Miranda, L., Collazo, J. A., 1997. Food habits of four species of wading birds (Ardidae) in a tropical mangrove swamp. Colonial Waterbirds 20(3): 413-418. Mock, D. W., 1981. White-dark polyphrmism in herons. Proceedings of the first Welder Wildlife Federation Symposium. Pp. 145-161. Mock, D. W., Lamey T. C, Ploger B. J., 1987. Proximate and ultimate roles of food amount in regulating egret sibling aggression. Ecology 68 (6): 1760 - 1772. Mock, D.W., 1987. Siblicide, Parent-offspring conflict, and unequal parental investment by egrets nad herons. Behav Ecol Sociobiol 20: 247-256. Mock, D.W., and Lamey T. C, 1991. The role of brood size in regulating egret sibling aggression, ^w. Nat. 138(4): 1015-1026. Monaghan, P., Walton, P, Uttley, J. D., and Bums, M. D. 1994. Effects pf prey behaviour on the foraging behaviour, diving efficiency and time allocation of breeding Guillemots Uria aalge. Ibis 136: 214 - 222. Moreau, R. E., 1944. Ecological Isolation in a rich tropical Avifauna. Ibis 86: 286-347. *Morisita, M. 1959. Measuring of interspeific association and similarity between communities. Mem. Fac. Sci. Kyushu. Univ. Ser. E. (Biol.) 3:65-80. Morrier, A., and McNeil, R., 1991. Time-activity budget of Wilson's and semi-palmated plovers in Tropical environment. Wilson Bull. 103 (4): 598 - 620. Morse, D. H., 1970. Ecological aspects of some mixed species foraging flocks of birds. Ecol. Monogr. 40: 119- 168. Morse, D. H., 1974. Niche breadth as a function of social dominance./iwA/ar 108: 818-810. 178 Parasharya, B.M.,1985. Pairing between pond heron and intermediate egret. Pavo 23:103- 104. Parasharya, B.M., and Bhat, H.R., 1987. Unusual feeding strategies of the little egret and pond heron. Pavo 25: 13-16. Parasharya B.M. & Naik R.M., 1984. The juvenile plumage of the little egret compared with that of the white phase Indian reef heron. J^iV/ZS' 81(3):693-695 Pasinelli, G., 2000. Sexual dimprphism and foraging niche partitioning in the middle spotted woodpecker Dedrocops medius Ibis 142: 635 - 644. Paulus, S. L., 1984. Activity budgets of non-breeding gadwalls in Lousiana. J. Wildl. Manage. 48(2): 371 -380. Peilou, E. C, 1972. Mathematical Ecology. Willey, Interscience NY, USA. Pennycuick, C. J., 1982. The flight of petrels nad albatrosses (Procellariiformes) observed in South Georgia and its vicinity. Phil. Trans. R. Soc. Land. 300: 75-105. Perrins, C. M., and Birkhead 1983. Avian Ecology. Blackie, Glasgow. Perennou, C. and Santharam, V., 1990. An Ornithological survey of some wetlands of south east India. J. Bom. Nat. Hist. Soc. 87(3): 354 - 363. Perennou, C, & MunkurT., 1991. Asian Waterfowl Census. 1991. IWRB, Slimbridge. Pianka, E. R. 1972. r and k selection or b and d se\ect\on? Am. Nat. 106:581-581. Pianka, E. R. 1974. Niche overlap and diffuse competition . Proc. Nad. Acad. Sci. 71: 2141 - 2154 Pianka, E. R., 1986. Ecology and Natural History of Desert Lizards. Princeton University Press, Princeton, NJ Pontin, A. J., 1982. Competition and Coexistence of Species. Pitman, London. Poysa, H, Elmberg J., Nummi P., Sjoberg K., 1996. Are ecomorphological associations among dabbling ducks consistent at a different spatial scale? Oikos 76(3):608-611. Prakash, V., 1999. Status of vultures in Keoladeo National Park, Bharatpur, Rajasthan, with special reference to population crash in Gyps species. J.Bom Nat. Hist. Soc. 96(3):365-378. Prater, S. H., 1971. The Bookof Indian Animals B^HS, Oxford University Press. 180 Prince, P. A., and Francis M. A., 1984. activity budgets of the foraging grey headed albatrosses. Condor 86: 297-300. Puiliam, H. R., and Milikan G. C, 1982. Social organization in the non-reproductive season. In: Avian Biology D. S. Famer, J. P. King and K. C. Parkas (Eds.). Acad Press. New York. Vol. 6, pp 169-197. Puiliam, H. R., and Caraco, T., 1984. Living in Groups: Is there an optimal group size? In: Behavioural Ecology J. R. Krebs and N. B. Davies (Eds.). 2"'' edition, Blackwell Scientific Publications, Oxford. Pp 122-147. Puiliam, H. R., 1985. Foraging efficiency, resource partitioning and the coexistence of sparrow species. Ecology 66: 1829 - 1836. Putman, R. J., 1996. Competition and Resource Partitioning in Temperate Ungulate Assemblies. Chapman and Hall, London. Pyke, G., Puiliam, H. R. and Chamove, E., 1977. Optimal foraging: a selective review of theory and test. Quarterly review of biology 52:137-154. Quinney, T. E., and Smith P. C, 1980. Comparative foraging behaviour and efficiency of adult and juvenile Great Blue herons. Can J. Zool. 58: 1168 - 1173. Rabenold, K. N., 1978. Foraging strategies, diversity and seasonality in bird communities of Appalachian spruce-fir forests. Ecol. Monogr. 48:397-424. Rahmani, A. R., and Manakadan, R., 1987. Interspecific behaviour of the Great Indian Bustard, Ardeoitis nigriceps. (Vigors.). J. Bom Nat Hist Soc. 84(2):317-331. Rahmani, A. R., and Sharma, S. N. 1997. Management Plan for Sheikha Jheel of Aligarh District. Centre of Wildlife and Ornithology, AMU & Hareetima Environmental Action Group. Rahmani, A., R., 2002. A thought for conservation of common birds. Mistnest3{2):]-2. Ramachandran, N. K., 1998. Interspecific associations of Jacanas Hydrophasianus chirurgus and Metopidius indicus) and the role of habitat. J. BOM. NAT. HIST. SOC. 95(1):76 - 86. Raveling, D. G., Crews, W.E., and Klimstra W. E., 1972. Activity patterns of Canada geese during winter Wilson Bulletin 84: 278 - 295. Razack, A., and Naik M., 1965. Studies on the Swift, 3. Awakening and roosting during the non-breeding period. Pavo 3:55-71. Recher, H. F., and J. A. Recher 1968. Comments on the escape of prey from avian predators, fico/ogy 49:560-562 181 Recher, H. F., and Recher, J. A., 1969. Comparative foraging efficiency of adult and immature Little Blue Herons Florida caerulea. Animal Behaviour. 17:320-322. Reeders, H. H., 1983. Spatial and temporal distribution of prey species of the Little Egret Egretta garzetta in a French Mediterranean wetland. Colonial Waterbirds 8:123-127. Reynolds, R. T., 1978. Food and habitat partitioning in two groups of coexisting accipiters. Ph. D. Dissertation. Oregon State University, USA. Rice, J., 1978. Ecological relationships of two inter specifically territorial vireos. Ecology 59:526-538. Ricklefs, R. E., 1983. Some considerations on the reproductive energetics of the pelagic sea birds. Colonial Waterbirds 13:1-6. Ricklefs, R E., and Schlutter D., (eds) 1993. Species diversity in ecological communities: historical and geographical perspectives. Chicago University Press, Chicago. Ricklefs, R. E., 2000. Lack, Skutch and Moreau the early development of life history thinking. Condor 102:3-8. Ripley, S. D. II, 1982. A Synopsis of the Birds of India and Pakistan. Bombay Natural History Society. Mumbai, India. Rhode, K., 1991. Intra and interspecific interactions in low density populations in resource rich habitats. Oikos 60:91-104. Robson, G. C, and Richards, O.W., 1936. The Variation ofNaimals in Nature. London. Rodgers, J. A., 1983. Foraging behaviour of seven species of herons in Tampa Bay, Florida. Colonial Waterbirds 6:11 -23 Rodgers, J. A., Jr. 1987. On the anti-predator advantages of coloniality: a word of caution. WillsonBull. 99:269-271. Rolando, A., Laiolo, P., and Formica, M., 1997. A comparative analysis of the foraging behaviour of the Chough Pyrrhocorax Pyrrhocorax and the Alpine Chough Pyrrhocorax graculus coexisting in the alps. Ibis 139: 461 - 467. Rosenzweig, M. L., 1981. A theory of habitat selection. Ecology 62:327-335. Rosenzweig, M. L., 1995. Species Diversity in Time and Space. Cambridge University Press, Cambridge. Rusterholtz, K. A., 1981a. Competition and the structure of an avian foraging guild. Am Nat 118:173-190. 182 Rusterholtz, K. A., 1981b. Niche overlap among foliage gleaning birds: support for Pianka's niche overlap hypothesis. Am. Nat. 117: 396 - 399. SACON 2004. Inland Wetlands of India. Unpublished Saxena, L. 1999. Description and classification of plant communities of Patna Bird Sanctuary and Sheikha Jheel. M.Sc. Dissertation, DWS, AMU, Aligarh. Sale, P. F., 1974. Overlap in resource use, and interspecific competition. Oecologia 17:245- 256. Schartz, R. L., and Zimmerman, J. L., 1971. Activity budget of the finches during non- breeding season. Condor 72: 113-121. Schoener, T., 1971. Theory of feeding strategies. Annual Review of Ecology and Systematics. 2:369-402. Schoener, T. W., 1974. Resource partitioning in ecological communities. Science 185:27-38. Schoener, T. W., 1982. The controversy over interspecific competition. American Scientist 70:586-582. Schoener, T. W., 1983. Field experiments on interspecific competition Am. Nat. 122:240- 285. Schoener, T. W., 1986. Resource Partitioning Pages 91 - 126. In Community Ecology: Pattern and Process. J. Kikakawa and D. J. Anderson (eds.) Blackwell Scientific Publication, Melbourbne, Austarlia. Scott, D., 1984. The feeding success of cattle egrets in flocks. Anim. Behav. 32:1089-1100. Seigfried, W. R., 1966. Time of departure from roost in the night heron. OstrichSl: 235-236. Seigfried, W. R., 1971. Communal roosting of cattle egrets. Trans. R. Soc. S. 4/r.39:419-433. Seigfried, W. R., 1971a. Feeding activity of the cattle egret Ardea 59: 38 - 46. Seigfried, W. R., 197 lb. Communal roosting of the Cattle Egret. Transactions of the Royal Society of South Africa 38: 419 - 443. Seigfred, W. R. 1976. Segregation in feeding behavior of four diving ducks in south Manitoba. Can. J. ofZool. 54(5):730 - 736. Seibert, H. C, 1951. Light intensity and the roosting flight of herons in New Jersey. Auk 68:63-74. 183 Seigel, S., 1956. Nonparametric Statistics from the Behavioural Science. New York: McGraw Hill. Sethi, N., 2005. Troubled Tiger: vanishing from Panna Tiger Reserve too. Down to Earth 13 (2):7-8. Shankar-Raman T. R., 2003. Assessment of census techniques for interspecific comparisons of tropical rainforest bird densities: field evaluation in Western Ghats, India. Ibis 145:9-21. Sherry, T. W., 1979. Competitive interactions and adaptive strategies of American Redstarts and Least Flycatchers in a northern hardwoods forest. Auk 96:265-283. Sherry, T. W., and Holmes, R. T., 1988. Habitat selection by breeding American Redstarts in response to a dominant competitor ,the Least Flycatcher. Auk 105:350-364. Simberioff, D., 1983. Competition theory: hypothesis testing and other community ecology buzzwords./iw. Nat. 122:626-625. *Singh, N., Sodhi, N.S., and Khera S., 1988. Biology of the Cattle egret Bubulcus ibis cormandus (Boddaert) Rec. Zool. Surv. India, Occ. Pap. 104:1-143. Singh, B., 1987. Uttar Pradesh District Gazetteer: Aligarh. Pub. Department of District Gazetteers, Government of UP, Lucknow. Sivasubramaniam, C, 1988. Aerial feeding by median egret {Egretta intermedia), little egret (Egretta garzetta) and pond heron {Ardeola grayii) JBNHS 85(3):611-612. *Sivakumar, K., Murugabhupathy, K., and Periaswamy, K., 1990. Ecology of egrets and the pond heron with special reference to population counts, time-activity budgets food habits and roosting behaviour. In: Seminar on wetland ecology and management. Bombay Natural History Society, Bombay. 154p. Skutch,A.F.,1949. Do tropical birds rear as many chicks as they can nourish? /Z)/591:403-407. Smith, J. M., 1976. Evolution and theory of games. American Sci. 64: 42 - 45. Smith, J. P., 1995. Nesting season food habits of 4 species of egrets and herons at Lake Okeechobee, Florida. Colonial Waterbirds20(2):\98-220. Snoddy, E. L., 1969. On the behavior and food habits of the cattle egret, Bubulcus ibis (L.). J. Georgia Entomol. Soc. 4(4): 156-158. Sodhi, N.S., and Khera, S., 1984. Food, food requirement during growth and feeding behaviour of nestling Bubulcus ibis cormandus (Boddaert) Pavo 184 Sodhi, N.S., 1986. Feeding ecology of Indian pond heron and its comparison with that of little egret. Pavo 24:97-116. *Sodhi, N.S., and Khera, S., 1986. Feeding habits of the median egret. Res. Bull. Punj. Univ. Sci. 37(1-2): 9-12. Sodhi, N.S., 1989. Monthly variations in diet of cattle egret Bubulcus ibis coromandus in and around Chandigarh. JBNHS 86 (3): 440-443. Sodhi, N.S., 1992. Food niche relationships of five sympatric north-Indian Herons. Forktail 7:125-130. Sprunt IV A., C. J. Ogden and S. Windckler {Eds.) 1978. Wading Birds. Research Report No. 7. International Audubon Society, New York. SPSS 200\. SPSS Base 11.0 User's Guide. SPSS Inc. 233, South Wacker Drive, Chicago. Sridharan, U., 1989. Comparative Ecology of Resident Ducks in Keoladeo National Park, Bharatpur, Rajasthan. Ph.D. Thesis, University of Bombay, Bombay. Sparling, D.W., and Krapu, G. L., 1994. Communal Roosting and foraging behaviour of staging sandhill cranes. Wilson Bull. 106(1):62 - 77. Steere, J. B., 1894. On the distribution of genera and species of non-migratory land-birds in the Phillipines. Ibis 1894:411-420. Stephens, D. W., and Krebs J. R., 1986. Foraging Theory. Princeton University Press, Princeton, New Jersey. Stutchbery, B. J., 1988. Evidence that bank swallow colonies do not function as information centres. Condor 90:953-955. Subramanya, S., 1996. Distribution, Status and conservation of Indian Heronries. J. Bom. Nat. Hist. Soc. 93(3):459-486. Tarburton, M. K., and Kaiser, E., 2001. Do fledgling and pre breeding common swifts Apus apus take part in aerial roosting? An answer from a radiotracking experiment. Ibis 143:255-263. Tebbich, S., Taborsky M., Fessl B., Dvorak M., and Winkler H., 2004. Feeding behaviour of four arboreal Darwin's Finches: Adaptations to spatial and seasonal variability. Condor \06: 95-105 Tamisier, A., 1976. Diurnal activities of green winged teal and pintal wintering in Louisiana. Wildlfiowl 27: 19 - 32. 185 Tilman, D. 1982. Resource Competition and Commnity Structure. Monographs in population biology - 17. Princeton University Press. Tilman, D. 1987. The importance of the mechanisms of interspecific competition. Am. Nat. 129: 769-774 Tiwari, J. K., and Rahmani, A. R., 1998. Large heronries in Kutch and the nesting of glossy ibis Plegadis falcinellus at Luna Jheel Kutch, Gujarat, India. J. Bom. Nat. Hist. Soc. 95(l):76-86. Thompson, C. F., Lanyon S. M., and Thompson K. M., 1982. The influence of foraging benefits on cattle egrets Bubulcus ibis with cattle. Oecologia 52: 167-170. Travis, J, and Trexler J., 1986. Interactions among foctors affecting growth,development and survival in experimental population of Bufo terrestris (Anura:Bufonidae). Oecology 69:110-116. Tripet, F., and Richner, H., 1997. Host response to ectoparasites: food compensation by parent blue tits. Oikos 78: 557 - 561. Tripet, F., Glaser, M., and Richner, H., 2002. Behavioural response to ectoparasite: time- budget adjustments and what matters to blue tits Parus caeruleus infested by fleas. Ibis 144: A6\-469. Turek, F. W., McMillan J. P., and Menaker, M., 1976. Melatonin alters the circadian rhythm of activity of sparrows. Science 194: 1441 - 1443. Udvardy, M. F. D., 1959. Notes on the ecological concepts of habitat and niche. Ecology 40:725-728. Urfi A.J., 1993. Heronries in the Delhi region of India. Oriental Bird Club Bull. 17:19-21. Urfi A.J., 1997. The significance of Delhi Zoo for wild waterbirds, with special reference to painted storks Mycteria leucocephala Forktail 12:87-98. Uthaman, P.K., 1990. Breeding of egrets in Kerala. y5A^//5 87(1): 139. Utley, J. D., Walton, P., Monaghan P., and Austin G., 1994. The effects of food abundance and breeding performance and adult time budgets of of Guillemots Uria aalge. Ibis 136:205-213. *Valverde, J. A., 1958. An Ecological sketch of the Goto Donana. Br. Birds 51: 1 - 23. van Vessem, J., and Draulans, D., 1986. The adaptive significance of colonial breeding in the grey heron Ardea cineria. Inter nad intra-colony variability in breeding success. OrnisScandivanica 17: 356-362. 186 Vandermeer, V., 1972. Niche Theory. Annual Review of ecology and Systematics. 3:107 -32. Venkatraman, C, 1996. Studies on the colonial waterbirds, and the characteristics of the Lake of the Vedanthangal Bird Sanctuary, Madras, Tamil Nadu, D. Phill. In Zoology, Madras University, Chennai. Vemer, J., 1965. Time budget of the male longbilled marsh wren during the breeding season. Condor 61: 125-139. Vessem, J. V., and Draulans D., 1987. Patterns of arrival and departure of Grey Herons at two breeding colonies. Ibis 129:353-363. Vijayan, V.S., 1975. The Ecological Isolation of Bulbuls (family Picnonotidae, Class Aves) with special reference to Pycnonotus cafer cafer (Linnaeus) and P. luteolus luteolus (Lesson) at Point Calimere, Tamilnadu. Ph.D. Diss. In Zoology, Univ. of Bombay. Vijayan, L., 1984. Comparative biology of Drongos (Family dicruridae class Aves) with special reference to ecological isolation. Ph.D. Thesis, University of Bombay. Vijayan, V. S., 2003. 'Where have all the sparrows gone?' Common bird conservation program SACON, Down to Earth Jan 2003. Volterra, V., 1926. Variations and fluctuations of the numbers of individuals in animal species living together. (Reprinted in 1931. In: Animal Ecology R. N. Chapman (ed.), MacGraw Hill, New York) Voute, A., Slutter, J. W., and Grimm, M. P., 1974. The influence of the natural light dark cycle on the activity rhythm of pond bats (Myotis dasycneme Boie 1825) during summer. Oecologia 17: 221 -243. Walsberg, G. E., and King, J. R., 1980. The thermoregulatory significance of the winter roos- site selected by robins in eastern Washington. Wilson Bull. 92(1): 33-39. Walsberg, G. E., 1986. The thermal consequences of roostsite selection: the relative importance of three modes of heat conservation. The Auk 103(l):l-7. Waltz, E. C, 1982. Resource characteristics and the evolution of information centres. Am. Nat. 190: 73 - 90. Ward, P., 1965. The feeding ecology of the blackfaced dioch Quelea quelea in Nigeria. Ibis 115:517-534. Ward, P., and Zahavi, A., 1973. The importance of certain assemblages of birds as information centres for food finding. Ibis 115:517- 534. Warham, J., 1990. The Petrels: their Ecology and Breeding Systems Academic Press, London. 187 Warham, J. 1996. The behaviour, Population Biology and Physiology of the Petrels Academic Press, London. Warkentin, I. G., and Morton, E. S., 2000. Flocking and foraging behaviour of wintering prothonotary warblers. Wilson Bull. 112(1):88-98. Wauters, L. A., Gurnell J., Martinolli A., Tosi G., 2002. Interspecific competition between native Eurasian red squirrels and alien grey squirrels: does resource partitioning occur. Behav Ecol Sociobiol 52:332-341. Webb, G. M., and Brotherson, J. D., 1988. Time-activity budgets pf drake gadwall and northern shovellers on industrial cooling ponds during late winter nad early spring in central Utah, Great Basin Naturalist 48(2): 280 - 284. Weatherhead, P. J., 1983. Two principle strategies in avian communal roosts. Am. Nat. 121:231-237. Weimerskirch, H. 1998. Foraging strategies of Southern Albatrosses and their relationship with fisheries In. Robertsen G. & Gales R. (eds) Albatross Biology and Conservation; 113 - 136. Chipping Norton, Surrey Beatly & Sons. Weimerskirch, H. and Guionnet, T., 1998. Comparative activity pattern during foraging of four albatross species. Ibis 144: 40 -50. Weins, J. A., 1989. The ecology of bird communities. In: Processes and Variations. Harness R. S. K, Birks H. J. B, Conner E. F., Harper J. L., Paine R. T. (eds.) Cambridge University Press, Cambridge. Wilbur, H. M., 1982. Competition between tadpoles of Hyla femoralis and Hyla gratiosa in laboratory experiments. Ecology 63:278-282. Wilbur, H. M., 1987. Regulation of structure in complex systems experimental pond • communities. Eco/ogy 68:1437-1452. Wiley, R. W., 197!. Activity periods and movements of the Eastern Woodrat. Southwest Nat. 16:43 - 54. Whittaker, R. H., and Levin S. A., 1975. Niche theory and Application. Dowdon, Hutchinson and Ross, Stoudsberg. White, D. H., and James D., 1978. Differential use of freshwater environments by wintering waterfowl of coastal Texas, Willson Bulletin 90:99 -111. Whitfield, A. K., and Babbler, S. J., 1979. Feeding ecology of piscivorous birds at Lake St. Lucia. Part 2: Wading birds. Ostrich 50: 1-9 Wildlife (Protection) Act 1972. As amended 1991, Wildlife Trust of India 188 Willard, D. E., 1977. The feeding ecology and behaviour of five species of herons in southeastern New Jersey. Condor 79: 462 - 470. Wijnandts, H., 1984. Ecological energetics of the long-eared owl Asia otus. Ardea 72:1-92. Wolf, L. L., and Heinsworth, F. R., 1971. Time and energy budgets of territorial hummingbirds. Ecology 52: 980 - 988. Wyne-Edwards, V. C, 1962. Animal Dispersion in Relation to Social Behaviour. New York pp. 653. Yahya H. S. A., 1980. A comparative study of the ecology and biology of Barbets Megalaima spp (Capitonidae:Piciformes) with special reference to Megalaima viridis (Boddaert) and Megalaima rubricapilla malabarica (Blyth) at the Periyar Tiger Reserve, Kerala. A Ph.D. thesis. University of Bombay. Yahya, H. S. A., 1987. Roosting behaviour of barbets {Megalaima spp.) In. Recent Trends in Ethology in India. (Eds.) M. Balakrishnan and K. M. Alexander. The Ehtological society of India, Bangalore. Yahya, H. S. A., Javed, S., and Ahmad, A., 1990. Ecology and Biology of some agricultural birds of Aligarh District. Report 1: Department of Science and Technology, Centre of Wildlife and Ornithology, AMU, Aligarh. Yahya, H. S. A., 2000. Food and feeding habits of Indian Barbets Megalaima Spp J. Bom. Nat. Hist. Soc. 97(1): 103-116 Yasmin, S., 1995. Ecology and biology of the Indian Peafowl pavo cristatus in the Aligarh Region. Ph.D. Thesis, Aligarh Muslim University. Zacharias, V. J., 1978. Ecology and Biology of certain species of Indian Babblers Turdoides Spp. In Malabar. Ph.D. Thesis. University of Calicut, Kerala. Zahavi, A., 1971. The function of pre-roost gatherings and communal roosts. Ibis 113: 106 - 109. Zador, S. G., and Piatt, J., 1999. Time budgets of common murres at a declining and increasing colony in Alaska. The Condor 101:149-152. Zar, J. H., 1986. Biostatistical Analysis. Prentice-Hall, Inc, Englewood Cliffs, N. J. *Zimmer, C, 1919. Der Beginn des Vogesanges in der Fruhdammerung Verh. Ornith. Ges. Bayern. 14:152-180. Original not seen 189 APPENDICES Appendix I List of plant species recorded at Sheikha Lake (2000 - 2004) .No. Scientific Name Family 1 Ipomea carnea Convolvulaceae 2 Evolvulus alsinoides Convolvulaceae 3 Convolvulus microphyllus Convolvulaceae 4 Wolffia Arrhiza Lemnaceae 5 Spirodela polyrrhiza Lemnaceae 6 Rumex dentatus Polygonaceae 7 Polygonum plebium Polygonaceae 8 Polygonum barbatum Polygonaceae 9 Desmodium Fabaceae 10 Alhagi pseudo-alghi Fabaceae 11 Melilotus indica Fabaceae 12 Prosopis juliflora Mimoaceae 13 Acacia nilotica Mimoaceae 14 Boerhavia rependa Nyctaginaceae 15 Boerhavia diffusa Nyctaginaceae 16 Hemigraphis Acanthaceae 27 Staurogyne hirta Acanthaceae 28 Rungia puncata Acanthaceae 19 Capparis horida Capparaceae 20 Capparis zeylanica Capparaceae 21 Capparis decidua Capparaceae 22 Ranunculus scleratus Ranunculaceae 23 Cissampelos parriera Menispermaceae 24 Cocculus hirsutus Menispermaceae 25 Tamarix dioca Tamariaceae 26 Abut Hon Malvaceae 27 Bombax ceiba Bombacaceae 28 Lagerstomia Sterculaceae 29 Azadirachta indica Meliaceae 30 Dalbergia sissoo Caesalpinaceae 190 31 Terminal i a arjuna Combretaceae 32 Eucalyptus lanceolatus Myrtaceae 34 Ludwig adscens Ongraceae 35 Coccinia cordifolia Cucurbitaceae 36 Zizyphus oenophela Rhamnaceae 37 Gnaphalium pulvinatum Asteraceae 38 Gnaphalium Asteraceae 39 Pluchea lanceolatus Asteraceae 40 Ageratum conizoides Asteraceae 41 Blumea Sps. Asteraceae 42 Eclipta prostrata Asteraceae 43 Laggera aurtia Asteraceae 44 Sonchus olearus Asteraceae 45 Erigeron ponariensis Asteraceae 46 Vernonia cineria Asteraceae 47 dehorium intybus Asteraceae 48 Lawnia nudicolis Asteraceae 49 Xanthium strumarium Asteraceae 50 Plumbago zeylanica Plumbaginaceae 51 Diospyros melanoxylon Ebenaceae 52 Calatropis procera Asclepediceae 53 Erithria ramosesimia Gentianaceae 54 Nymphoides cristata Gentianaceae 55 Heliotropium Borgaginaceae 56 Cordia dichotoma Borgaginaceae 57 Nicotiana plumbagifolia Solanaceae 58 Withania somnifera Solanaceae 59 Solanum nigrum Solanaceae 60 Mazus japonicus Scrophulariaceae 61 Vernnica anagallis-aquatica Scrophulariaceae 62 Bacopa monnieri Scrophulariaceae 63 Utricularia Lentibulariaceae 64 Phyla nodiflora Verbenaceae 65 Lantana camra Verbenaceae 66 Achrynthus asper Amaranthaceae 67 Amranthus Amaranthaceae 68 Chenopodium murale Chenopodiaceae 69 Chenopodium album Chenopodiaceae 191 70 Euphorbia hirta Euphorbiacea 71 Khngalia Euphorbiacea 72 Syzigium cuminii Moraceae 73 Ceratophyllum demersum Ceratophyllaceae 74 Zeuxine Orchidaceae 75 Commelina benghalensis Commelinaceae 76 Eichornia crassiseps Pontederiaceae 77 Typha anguistata Typhaceae 78 Potamogeton nodosus Potamogetonaceae 79 Cyperus rotundus Cyperaceae 80 Fimbristylis Cyperaceae 81 Scripus Cyperaceae 82 Ergrostis japonica Poaceae 83 Paspalidium gemimatum Poaceae 84 Arudo donax Poaceae 85 Saccharum munja Poaceae 86 Saccharum spontaneum Poaceae 87 Imperata cylindrica Poaceae 88 Dicanthium annulatum Poaceae 89 Phalaris minor Poaceae 90 Sporobolus annulatum Poaceae 91 Paspalum distichum Poaceae 92 Poa annua Poaceae 93 Desmostacchya bipinnata Poaceae 94 Cynodon dactylon Poaceae 95 Polypogon monospeliensis Poaceae 96 Cenchrus ciliaris Poaceae 97 Phragmites karka Poaceae 98 Equisetum Pteridophytes 99 Azolla Pteridophytes 100 Marsilea Pteridophytes 192 Appendix II List of birds recorded in the environs of Sheikha Lake (2001 - 2004) S.No. Name Status 1. Little Grebe Tachyhaptus rufficolis C,R 2. Great Crested Grebe Podiceps cristatus UN, M 3. Cormorant phalacrocorax carbo R,UN 4. Little Cormorant Phalacrocorax niger C,R 5. Darter Anhinga rufa C,R 6. Little Egret Egretta garzetta C,R 7. Great Egret Casmerodius albus C,R 8. Intermediate Egret Egretta intermedia C,R 9. Cattle Egret Bubulcus ibis C,R 10. Ind-ion ?ond Heron Ardeolagrayii C,R 11. Grey Heron Ardea cinerea C,R 12. Purple Heron Ardea purpurea C,R 13. Black-crowned Night Heron A^j^c^/corax «yc//corax C,R 14. Glossy Ibis Plegadis facinellus C,R 15. Black-headed Ibis Threkiornis aethiopica C,R 16. ^\?ic\^Vc>\s Pseudibis papulosa C,R 17. Painted Stork Mycteria leucocephala C,R 18. Open bill Stork Anastomus oscitans C,R 19. Woolly-necked Stork Ciconia episcopus C,R 20. Black-necked Stork Ephippiorhynchus asiaticus UN, R 21. Eurasian spoonbill P/ato/ea/ewcoroc/ja UN,R 22. Greylag Goose Anser anser C,M 23. Bar headed Goose Anser indicus C,M 24. Lesser Whistling Teal Dendrocygnajavanica C,R 25. Ruddy Shelduck Tadorna ferruginea C,M 26. Pintail Anas acuta C,M 27. Common Teal Anas crecca C,M 28. ^po\h\\\eAT>ViC]f. Anas poecilorhyncha C,M 29. Mallard Anas platyrhynchos UN,M 193 30. Gadwall Anas strepera C,M 31. Enrsian Wigeon Anas penelope C,M 32. Shoveller Anas dypeata C,M 33. Common Pochard Aythya ferrina C,M 34. Cotton Pygmy-Goose Nettapus coromendelianus C,R 35. Comb Duck Sarkidiornis melanotos C,R 38. Osprey Pandion haliaetus UN,M 37. Black-shouldered Kite Elanus caeruleus C,R 38. Money ^uzzarA Pernis ptilorhyncus C,R 39. Black Kite Milvus migrans C,R 40. Brahminy Kite Haliastur indus C,R 41. Egy^\xdiXi\w\X\xxQ Neophron percnopterus C,R 42. Short-toed snake Eagle Circaetus gallicus UN, R 43. Crested Serpent Eagle Spilornis cheela C,R 44. Eurasian Marsh Harrier Circus aeruginosus C,R 45. Shikra Accipiter badius C,R 46. OnenlaWioney-Buzzard Pernisptilorhynchus C,R 47. White-Eyed Buzzard Butastur teesa C,R 48. Greater Spotted Eagle Aquila clanga UN,M 49. Tawny Eagle Aquilla rapax C,R 50. Steppe Eagle Aquila nipalensis C,M 51. Common Kestrel Fa/co Cmnwncw/wi' C,R 52. Grey Francolin Francolinus pondicerianus C,R 53. Common Peafowl Pavo cristatus C,R 54. Sams Crane Grus antigone C,R 55. White-breasted Water hen y^maMrowwp/zoen/cMrw^ C,R 56. Brown Crake Amaurnis akool UN,R 57. Common Moorhen Gallinula chloropus C,R 58. ?\xr()\t'&^av[vph.tn Porphyria porphyria C,R 59. Common Coot Fulica atra C,M 60. Pheasant-tail Jacana Hydrophasianus chirurgus C,R 61. BxonzQ-yi'mgcd iacana Metopidius indicus C,R 62. Painted Snipe Rostratula bengalesis C,R 63. Black-winged Stilt Himantopus himantopus C,LM 64. Avocet Recurvirostra avesetta UN,M 65. Stone Curlew Burhinus oedinemus C,R 66. Indian Courser Cirsorius coromandelicus C, LM 67. Large Indian Pratincole Glareolapratincola C, LM 194 68. Small Indian Pratincole Glareola lacteal C, LM 69. White-tailed Lapwing Vanellus leucurus C,M 70. Redwattled Lapwing Vanellus indicus C,R 71. Yellow-wattled Lapwing F(ane//M5/«a/fl6ar/CM5 C,M 72. Little Ringed Plover Charadrius dubius C,M 73. Kentish Plover Charadrius alexandricus C,M 74. Black-tailed Godwit Limosa limosa C,M 75. Spotted Redshank Tringa erythropus C,M 76. Greenshank Tringa nebularia C,M 77. Marsh sandpiper Tringa stegantiUs C,M 78. Green sandpiper Tringa ochropus C,M 79. Wood sandpiper Tringa glareola C,M 80. Common sandpiper Tringa hypoleucos C,M 81. VdinXdi\\ Sni^iQ Gallinago gallinago C,M 82. Pintail Snipe Gallinago steruna C,M 83. Little Stint Calidris minuta C,M 84. Temminck's Stint Calidris teminckii C,M 85. Ruff & Reeve Philomacuspugnax C,M 86. Black headed Gull Lams ridibundus C,M 87. Indian River tern Sterna aurantia C,R 88. Black-bellied tern Sterna acuticauda C,LM 89. Yellow legged green pigeon Treron phoenicoptera C,R 90. Indian Ring Dove Streptopelia decaocto C,R 91. Red Turtle Dove Streptopelia tranquebarica C,R 92. Little Brown Dove Streptopelia sengalensis C,R 93. Blue Rock Pigeon columba livia C,R 94. Rose ringed Parakeet Psittacula kramerii C,R 95. Blossom headed Parakeet Psittacula cyanocephala C,R 96. Pied Crested Cuckoo Clamator jacobinus C,LM 97. Brain fever Bird Culculus varius C,M 98. Koel Eudynamus scolopacea C,R 99. Crow-Pheasant Centropus sinensis C,R 100. Spotted Owlet Athene brama C,R 101. Honse Sv/\ft Apus qffinis C,R 102. Palm Swift Cypsiurus parvus C,R 103. Lesser Pied Kingfisher Ceryle rudis C,R 104. Common Kingfisher ^/cec/oarr^j.y C,R 105. White breasted Kingfisher//a/cyo« ^w/>e«-yw C,R 195 106. Green Bee-eater Merops orientalis C,LM 107. Indian Roller Coracias benghalensis C,R 108. Hoopoe Upupa epops C,R 109. Common Grey Hombill Tockus birostris C,LM 110. Large Green Barbet Megalaima zeylanica C,R 111. CoppersmiXh Megalaima haemacephala C,R 112. Ashy crowned Finch-Lark £remop?ra gmea C,R 113. Rufous tailed Finch-Lark Ammomamsphoenicurus C,LM 114. Short toed Lark Calandrella cinerea C,M 115. Crested Lark Galerida cristata C,R 116. Eastern Skylark Alauada gulgula C,R 117. Sv/allov/Hirundo rustika C,R 118. Wiretailed Swallow///>w«Jo 5OT/7/2/Z C,R 119. Redrumped Swallow///>w«c/o c/awnca C,R 120. House Martin Delichonurbica C,R 121. Grey Shrike Lanius excubitor C,R 122. Bay backed Shrike Lanius vittatus C,R 123. Rufous backed Shrike Lanius schach C,M 124. Brov^nShiike Lanius cristautus C,M 125. Black Drongo Dicrurus adsimilis C,R 126. Brahminy Myna Sturnus pagodarum C,R 127. Vxedyiyna Sturnus contra C,R 128. Rosy ?astor Sturnus roseus C,R 129. CommonMyna Acridotheres tristis C,R 130. Bank Myna Acredotheres ginginianus C,R 131. House Crow Corvus splendens C,R 132. Jungle Crow Corvus macrorhynchos C,R 133. Red-vented Bulbul/'>'cnonoft 196 144. Bluethroat Ehthacus sveecicus C,M 145. Magpie Robin Copsychus saularis C,R 146. Indian Robin Saxicolides fulicata C,R 147. Black Redstart Phoenicurus ochrurus C,R 148. Brown Rock Chat S'ercowe/fl/w^ca C,R 149. Stone Chat Saxicola torquata C,M 150. Pied Bushchat Saxicola caprata C,R 151. Idmny ¥\^i\ Anthus campestris C,M 152. VsddyfiQldVxTgixXAnthus novaseelandie C,M 153. Yellow Wagtail Motacilla flava C,M 154. Yellowheaded Wagtail Motoc///a c;Yreo/a C,M 155. Grey Wagtail A/otoc///(3 cmer/a C,M 156. White Wagtail Motacilla alba C,M 157. Large Pied Wagtail Mo/aci7/fl mac/era5pare«5/5 C,R 158. Purple Sunbird Nectarina asiatica C,R 159. WousQ ^Tpdivrov^ Passer domesticus C,R 160. Bay^ Ploceus philippinus C,R 161. KedMrniia Estrilda amandava C,R 162. Whitethroated Munia Lonchura malabarica C,R C=Common, UN=Uncommon, M=Migrant, R=Resident, LM=Local migrant Nomenclature based upon Grimmett ef a/, (f 998) and Grimmett et a/. (2000) 197 u 1_ u o .Q cu (N ON 00 o in E ^ 00 o o y) S » o "(Q o o o o o o •M s ^ VJ O o L. —: (N (L) ^ ON 5 o if) JS rtJ 0) 6X1 1_ ai CJ> lA OJ fi .^J c V 00 ••tj V4— "S U ON U) ro ON NO a; o s in rn to M ^ NO 00 0) "2 in (N I/) 0) c o ^ ^ ""^ Tf ]> -H -H u •S .2 -H -H -H -H -H t— ,a r^ r- in ON i3 Q. -3 JZ 1/1 O NO en U i- 'j_ \n •4-1 9J V) fO £t (U Q. s E 9 a *< a. p^ in a (N ^^ (N NO NO -^nd bXu ) ro ro O ro T3 a> C -*< o c ON Tj- in Ti- ^ •~" '•i-> Tf (4— 01 ON in in in O o o 5 V- o -H -H -H (U 1_ +1 -H -H -H JD k_ in ON rn 00 E o< O in 3 £ - OJ in 00 o c Q. "TO ^ •!-> o >^ •i-J CL V4— o o c C fD ro U ^^ u OJ ^r s Z o o • • < IS o rsi ^-^ ^•^ o^ ^ ^ 1) O oin^ ^6 a in r- 9) o o a S3 1 1 in < A CL, _u 1 in o r~~ R) u C/5 E in CNI in A H 1- O (N ro H V) fees .y ^ m r- rn ro —' o in o Q. tu ^ o '—' -H -H -H -H m (N '^ P rj 5 CO ha; mf^ .5f