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Community structure and habitat associations of lowland grassland birds in Nepal.
Baral, H.S.
Publication date 2001
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Citation for published version (APA): Baral, H. S. (2001). Community structure and habitat associations of lowland grassland birds in Nepal. UvA/Cardiff University.
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Download date:26 Sep 2021 CHAPTERR 2 STUDYY AREAS AND METHODS
2.1.. Description of the study areas Nepal'ss tall grasslands are found in the fertile Gangetic plain in the southern part of the country (Figuree 1.1). Formerly they were more or less continuous from west to east. At present five protectedd areas are located in this region, all of them lying within more or less the same subtropical ecologicall zone. Together these protected areas comprise a total of 272 900 ha of land, of which roughlyy 50 000 ha is estimated to be grasslands in various forms (Table 2.1). One of these areas, Parsaa Wildlife Reserve (hereafter 'Parsa'), can be taken as the continuation of the Royal Chitwan Nationall Park (hereafter 'Chitwan', 27°15' - 27°35/N / 83°45' - 84°58'E). Parsa does not have extensivee grasslands. Two of the protected areas, Chitwan and Royal Sukila Phanta Wildlife Reserve (hereafterr 'Sukila Phanta', 28°49' - 28°57' N / 80°07' - 80° 15' E), were chosen for the execution of myy study. These both reserves have a diverse assemblage of grasses representing most lowland grasslandd types (Peet et al. 1999). In addition, I have also made some observations in the east at Koshii Tappu Wildlife Reserve (hereafter 'Koshi Tappu', 26° 35' - 26° 40' N / 86° 56' - 87° 04' E) inn 1996 and 1997.
Sukilaa Phanta lies in the extreme southwest of the terai and is the smallest of the protected areas coveringg 15 500 ha, ranging in altitude from 90 m to 270 m (IUCN 1993, Figure 2.1). Some 54.7% of thee reserve is covered by mixed deciduous forest, grassland and marsh in the southwest where soils aree of recent alluvium. The rest is moist deciduous forest and savannah, supported by better-drained soilss on higher terrain in the northeast (IUCN 1993). The reserve possesses the largest grassland phantass in Nepal. A plan to extend the reserve on its eastern side has been long pending. When this iss realised and protection is afforded, the total area of Sukila Phanta will be 30 500 ha (Tirtha Man Maskeyy pers. comm. 1996) and more phantas could be created. Sukila Phanta has a hot and dry monsoonall climate (Table 2.2). A warm and dry westerly wind blows across the phantas during the latee afternoon generally settling before sunset, particularly in the months of April and May. This windd considerably reduced bird activities.
AA total of 30 species of mammals and over 350 species of birds have been definitely recorded in the reservee (Himalayan Nature 2000). The grasslands at Sukila Phanta support a high population of Bengall Florican Houbaropsis bengalensis (Inskipp and Inskipp 1983), Swamp Francolin FrancolinusFrancolinus gularis (Baral 1998a) Bristled Grassbird Chaetornis striatus (Baral 1997) and Hodgson'ss Bushchat Saxicola insignis (Baral 1998c), taxa considered to be globally threatened (Collarr etal. 1994, Table 2.1). Recently, two grassland birds that were found in Sukila Phanta were presentedd as new species for Nepal indicating that the grasslands here were poorly surveyed until noww (Baral 1998b). One of these, Finn's Weaver Ploceus megarhynchus, is considered globally
11 1 STUDYY AREAS AND METHODS
Tablee 2.1. National Parks and Wildlife Reserves in lowland Nepal. The number of globally (threatenedd and near-threatened) and nationally threatened bird species is also given.
Parks/Reserves s Areaa ha. Approx. . Forestt ha. Nanl l Globl l Location n grassland d spp. . spp. . ha. . Royall Sukila Phanta WR 16500 0 7600 0 8900 0 18 8 6 6 Farr west Royall Bardia NP 96800 0 19000 0 77800 0 14 4 4 4 West t Royall Chitwan NP 93200 0 18500 0 74700 0 16 6 9 9 Central l Koshii Tappu WR 17500 0 6000 0 11500 0 12 2 7 7 East t Total l 224000 0 51100 0 172900 0 Source:: Department of National Parks and Wildlife Conservation (HMG of Nepal), Collar et al. (1994), Barall et al. (1996)
Tablee 2.2. Climatological data for Sukila Phanta and Chitwan
Temperature e Humidity y Precipitation n
Chitwan n Maximum m Minimum m 0845hrs s 1745hrs s (mm) ) (Celsius) ) (Celsius) ) 1995 5 NA A NA A 77 7 70 0 1778 8 Average e 1996 6 31 1 18.10 0 84 4 77 7 1784 4 Average e 1997 7 31 1 17.2 2 82 2 67 7 2141 1 Average e 1998 8 31 1 19.1 1 85.9 9 71.9 9 NA A Average e Sukilaa Phanta 1995 5 30 0 17.3 3 74.02 2 78.95 5 1591 1 Average e 1996 6 31 1 18.06 6 79 9 68 8 1643 3 Average e 1997 7 NA A NA A NA A NA A 1625 5 Average e 1998 8 30 0 NA A 81.4 4 68.4 4 NA A Average e NA:: Not Available (Source: Department of Meteorology and Hydrology, HMG of Nepal)
12 2 STUDYY AREAS AND METHODS
threatenedd (Collar et al. 1994) and was previously described as endemic to India (Ali and Ripley 1987).. Additionally, Sukila Phanta supports a large population of Swamp Deer Cervus duvauceli duvauceli,, a globally threatened mammal species (Schaff 1978, Groombridge 1993).
Chitwann is an inner doon valley in the central terai of Nepal between the Siwalik hills in the south andd the Mahabharat hills to the north. All other protected areas in lowland Nepal lie beyond the finalfinal range of hills. The park ranges in altitude from 150 m to 815 m (IUCN 1993). The total area of Chitwann is 93 200 ha. and is bordered by Parsa Wildlife Reserve (49 900 ha) in the east. It is located inn the drainage basin of three major rivers: Narayani, Rapti and Reu (Figure 2.2) and has a more humidd environment than Sukila Phanta (Table 2.2). Chitwan has numerous small patches of grasslands,, lying alongside the rivers. These riverside grasslands vary in width from few meters to 15000 m. Approximately 70% of the park is covered by sal forest (Laurie 1979), the remainder being grasslandd and riverine forests (Gurung 1983).
Moree than 50 species of mammals and a high total of 526 bird species have been recorded in Chitwann (Baral and Upadhayay 1998). It is an important site for grassland birds, particularly for HoubaropsisHoubaropsis bengalensis (Inskipp and Inskipp 1983), Lesser Florican Sypheotides indica (Inskipp andd Inskipp 1991), Jerdon's Babbler Chrysomma altirostre (Baral and Eames 1991), Slender-billed Babblerr Turdoides longirostris (H. S. Baral in prep.), Bristled Grassbird (Baral 1997) and Grey- crownedd Prinia Prinia cinereocapilla (H. S. Baral in prep.) (Table 2.1). Chitwan is the only locality inn Nepal where Turdoides longirostris has been recorded. Chitwan also supports a quarter of the worldd population of the Greater One-horned Rhinoceros Rhinoceros unicornis, a globally threatened mammall (Laurie 1982, Groombridge 1993).
Koshii Tappu occupies 17 500 ha of the Sapta Koshi River floodplain at the most northeasterly extensionn of the Gangetic Plain. It ranges in altitude from 75-81 m (IUCN 1993). The reserve is locatedd between two flood control embankments and is subject to annual flooding. Approximately 70%% of the reserve's land area is covered in grasslands (Heinen 1993b), although during high flood yearss a large amount of grassland is destroyed and replaced by new alluvial deposits. The reserve containss Nepal's last population of Asiatic Wild Buffalo Bubalus arnee, a globally threatened speciess (Groombridge 1993). Koshi Tappu is further protected as a Ramsar Site for its importance forr migrating wildfowl (IUCN 1993). Besides being an important site for migrating waterfowl, Koshi Tappuu is important for grassland birds like Houbaropsis bengalensis (Inskipp and Inskipp 1983), SaxicolaSaxicola insignis (Inskipp and Inskipp 1991), Francolinus gularis (Baral 1998b), and Chaetornis striatusstriatus (H. S. Baral in prep). The reserve faces severe problems of illegal grazing, fodder collection, treee felling and hunting from the surrounding villages (Giri 1997, Petersson 1998).
13 3 STUDYY AREAS AND METHODS
> > ca a c c If) If)
ca a a a 2 2 (X X 1 11 1 i i
0 0 0 0
0 0 / / 1 1 I I \ \ J J TO TO c c TO TO
Q. . _TO O / /
CO O
Figuree 2.1. Sukila Phanta Wildlife Reserve with transects shown.
14 4 STUDYY AREAS AND METHODS
Royall Chitwan National Park
Habitat t CYMB B FRST T [CNP P MPC C IMPL L NARP P PK K Ploughed d SAL L SS S SSSB B THEA A TILLAGE E WHEAT T
transects
Miles s
00 12 3
Figuree 2.2. Royal Chitwan National Park with transects shown.
15 5 STUDYY AREAS AND METHODS
2.2.. Methods Thee general strategy of the work was to collect environmental and bird data from sections of all the areass outlined above. Bird and environmental data wuld then be related together using multivariate techniques.. Also, the distribution of scarce and threatened species would be assessed, and variations inn their richness between locations appraised.
2.2.1.. WORK, PLANNING Inn recent years, several books and papers have been published describing the methods and problems off carrying out biological surveys in the field. Basic information on the best methods for this study wass taken from Bibby et al. (1992). The line transect count was adopted as the main method for surveyingg the grassland bird populations. Ideally, transects should be of equal length and should be surveyedd an equal number of times in the various seasons. Logistical difficulties, which are elaboratedd upon in the next section, prevented such a regular pattern of surveys. Also, the structure off the habitat caused the transects to be of different lengths.
Thee first year of the study, 1996, was used to become acquainted with the study areas and survey routines.. Most transects were laid out. In principle, a transect is a straight path, running through the grasslandd at right angles to a river, extending from the river to the forest. Where possible, such linear transectss were laid out in different grassland types in the three study sites. As far as possible the numberr of sections of each habitat type on a transect represented the proportionate distribution of habitatss within each region. The length of transects varied from 100 m to 1100 m. Each transect was dividedd into sections of 100 m to standardise observations. Habitat data were recorded along each 1000 m section. In the two succeeding years efforts were made to work most transects as often as possiblee (Tables 2.3 and 2.4). It soon became apparent that it would be impossible to work three studyy areas because of logistical and time factors. So it was decided that Koshi Tappu would no longerr be studied systematically (Table 2.5).
Transectss in Sukila Phanta and Chitwan were visited in 1996, 1997 and 1998 from December until May.. Koshi Tappu was visited in 1996 and 1997 in March, April and May. Every transect was coveredd at least 3 times. Conditions in the field were such that no systematic observations of birds couldd be made during the monsoon season, from June to November. The number of times any transectt was worked during the years 1997 and 1998 varied between 1 and 17 (Tables 2.3-5).
2.2.2.. SELECTING TRANSECTS Severall factors restricted the selection of transects. All grasslands were inhabited by a variety of potentiall dangerous large mammals such as tiger, rhino, gaur, sloth bear, wild buffalo (Koshi Tappu) andd wild boar. Consequently, working in the grasslands on foot involved a significant risk from animall attack. Data were usually collected when disturbance by tourists and villagers was minimal to reducee the effect of disturbance on the recording of bird species. This time period also coincided
16 6 STUDYY AREAS AND METHODS
Tablee 2.3. Transects and sections in Chitwan
Chitwan n Transect tJNro f f jj Nr of visits !! sections 11 W96 S966 I W97 7 S977 ! W98 8 S988 I Total l 1 1 \\ 2 !! 13 99 \ 0 0 77 j 1 1 00 1 30 0 2 2 11 3 11 17 133 I 1 1 99 1 77 I 66 j 53 3 3 3 !! 2 11 14 277 ! 2 2 66 1 88 ! 55 1 62 2 4 4 jj 3 II 1 22 1 1 1 66 | 100 I 55 | 25 5 5 5 !! 7 11 0 33 ! 0 0 22 ! ioo ! 55 i 20 0 6 6 !! 2 !! o 33 1 0 0 77 | 177 | 55 ! 32 2 7 7 ii 2 11 0 1 11 1 0 0 22 1 111 1 55 i 19 9 8 8 11 6 11 o j 00 I 0 0 44 | 99 ! 55 I 18 8 9 9 4 4 11 o | 00 i 1 1 44 ! 55 1 33 1 13 3 10 0 11 7 !! o 1 66 I 33 ! 44 1 133 I 44 ! 36 6 11 1 11 1 11 o ! 33 1 11 I 55 1 00 ! 00 1 9 9 12 2 11 5 11 0 33 I 11 1 66 j 100 ! 44 ! 24 4 13 3 11 3 !! o 1 33 1 11 1 44 ! 33 ! 33 ! 14 4 15 5 II 1 11 o ! 33 ! 22 j 100 ! 11 | 00 1 16 6 16 6 !! 3 11 o | 22 1 00 1 33 1 55 ! 11 i 11 1 17 7 11 3 !! o ! 22 j 11 1 44 I oo ! 00 1 7 7 18 8 11 6 ii o I 22 ! ii ! 44 ! 44 ! 22 1 13 3 19 9 !! 3 !! o I 22 j ll i 44 1 oo 1 oo ! 7 7 21 1 !! n 11 0 1 22 1 oo ! 33 i 99 1 66 1 20 0 23 3 !! i !! o 1 00 1 ll ! 66 1 00 1 oo ! 7 7 24 4 11 2 ii o 1 00 ! oo ! 55 1 66 ! 33 1 14 4 25 5 11 6 11 o i 100 1 ll 1 55 j 122 1 55 j 33 3 26 6 !! 6 11 0 1 11 ! oo ! 111 i iii ! 66 i 26 6 27 7 !! 1 !! o 1 00 1 ll ! 66 1 ioo ! 00 1 17 7 28 8 11 2 !! o 1 00 1 oo ! 55 ! 99 ! oo ! 14 4 29 9 !! 4 !! o ! 00 \ ll 1 44 ! 55 ! 22 | 12 2 30 0 11 2 11 0 1 00 1 00 1 00 1 66 1 44 \ 10 0 Total l 11 98 11 45 1 977 j 200 1 1366 I 1822 1 799 1 562 2 ÏTUDYY AREAS AND METHODS
Tablee 2.4. Transects and sections in Sukila Phanta
SUKILAA PHANTA
Transectt 1 Nr of Numberr of visits sections s !! W96 ! S96 6!! W97 ! S97 ! W98 ! S98 !! Total 11 5 ;; 0 i 4 4 11 8 | 7 | 0 | 6 !! 25 22 1 1 ii 0 i 0 0 || 2 | 0 j 0 | 0 !! 2 44 ! 6 ii 0 ! 0 0 jj 5 | 6 | 5 j 9, || 25 55 1 4 ii o i 5 5 || 7 | 6 ! 5110 11 33 66 ! 6 !! 0 ! 4 4 || 4 | 6 ! 0 j q_ 11 14 77 ! 6 !! o 1 4 4 || 4 | 6 | 5 | 10 jj 29 88 1 9 !! o i 4 4 jj 5 | 6 | 5 | 10 || 30 99 ! 6 ii o i 6 6 || 7 j 6 | 5 | iÖ !! 34 100 6 !! o | 5 5 !! 5 ! 6 ! 5 1 10 11 31 111 1 6 ii 0 i 3 3 || 5 | 6 | 5 }?_ jj 28 122 1 6 !! o i 0 0 || 5 | 6 | 0 J 10 11 21 133 ! 3 ii o i 0 0 11 6 ! 6 | 0 | 0 11 12 144 ! 3 ii o i 0 0 || 5 j 6 | q } q !! ii 155 1 3 ii o i 0 0 || 5 | 6 j 0}10 !! 21 166 1 3 ii o i 0 0 || 7 | 7 | 5 j ii || 30 177 i 2 !! o i 0 0 || 2 | 6 1.5jiq || 23 188 ! 6 ii 0 i 0 0 || 0 ; 5 } 5{10 || 20 200 1 3 ii o i 0 0 || o 1 q 1 q } i_q 11 io 211 i 3 :: 0 i 0 0 || o | o j q | iq !! io 222 i 3 ii 0 i 0 0 || ö | Ö' | o ! i"511 10 Totall 90 II 0 i 35 5 11 82 1 97 1 50 ! 155 !! 419
Tablee 2.5. Transects and sections in Koshi Tappu
Koshii Tappu Transect t Nrof f II S97 sections s 1 1 1 1 !! 4 2 2 1 1 11 4 3 3 2 2 !! 3 4 4 2 2 11 4 5 5 2 2 jj 5 6 6 3 3 !! 3 7 7 2 2 11 2 8 8 3 3 !! 2 9 9 4 4 11 2 Total l 20 0 11 29
18 8 STUDYY AREAS AND METHODS withh the activities of the large mammals. I had several close encounters with them during the fieldworkfieldwork and this was intensified towards last year because of an increase in their numbers.
Inn many areas tall grasses obstructed visibility. To maximise visibility for the detection of both grasslandd birds and large mammals, I mostly followed existing dirt tracks through the grasslands. In placess where there were no tracks, a 3 to 4 m wide area was cleared through the grassland to make a transect.. Efforts to make transects through the grasslands took considerable time and expense. In moistt and wet grassland habitats which were difficult to walk, no transects could be made at all simplyy because of inaccessibility or for safety reasons. Such places could be dangerous because of thee risk of an encounter with a large mammal. Two grassland habitats Typha elephantina (TYEL) andd Phragmites karka (PK) (Peet et al. 1999) could not be covered well by this survey. The former typee of grasslands existed only in Koshi Tappu area and was extensive only outside the reserve. Thee largest Phragmites karka grassland occurred in Sukila Phanta and was not penetrable even by thee best trained of the domestic elephants.
2.2.3.. ENVIRONMENTAL DATA AA data sheet for habitat was prepared for each transect (Appendix 1). If notable changes had taken placee between two visits (either natural or man-made), a new habitat sheet was made. The importancee of recording enough habitat variables for easy interpretation of bird distribution in relationn to the habitat was recognised from the start. These variables were: grass species composition,, soil moisture, phenophase of grasses, average grass height, percentage of bare ground, presencee of vegetation other than grasses, and if present their percentage, type and average height, grazingg pressure, data on whether the area had been burnt or cut, disturbance by people, proximity too water and forest. Environmental variables measured were true for 100 m on either side of the transectt section. Beyond this distance the vegetation data may not be true. The following paragraphss explain how the habitat variables were scored.
Forr burning, cutting and digging by wild animals a numerical score from 0 to 3 was devised in an increasingg order of intensity (Table 2.6). All grassland sites were coded depending upon their proximityy to different forest types (Table 2.7). In some analyses 'Intermediate Grassland' sites weree further divided into 2 categories depending upon the amount of emergent vegetation present in them.. 'Emergent Intermediate': 10% emergent vegetation; 'Open Intermediate': <10% emergent vegetationn (Table 5.1). Soil moisture and grazing were coded on a scale from 1 to 3 in an increasing orderr (Table 2.8) Grazing intensity codes apply to both cattle grazing and wild grazing. For grazing byy livestock the term 'Cattle Grazing' is employed. The grass species were coded in four abundance scaless based on their percentage coverage at a site (Table 2.8).
19 9 STUDYY AREAS AND METHODS
Tablee 2.6. Scoring of burning, cutting and digging by wild animals
Burning g Scoree I jj Cutting !! Score I jj Digging Score e Unburnt t öö |jj Uncut 11 ° 1jj No digging 0 0 Burningg <=25% ÏÏ |" || Cutting <=25% || Ï |JJ Little (<15%) r r Burningg >25<50% 22 j [Cuttingg >25<50% ii 2 i'TN^rate'(Ï5-2_'. . . 2 2 Burningg >=50% 33 j jj Cutting >=50% 11 3 ! jj Extensive (50%) 3 3
Tablee 2.7. Scoring of distance from forest
Habitat t jj Forest distance (m) 1Cod e e Sall forests !! 0-100 ! 1 1 Riverinee forests || 0-100 | 2 2 Mixedd forests || 0-100 j 3 3 Intermediatee grasslands 11 101-500 ! 4 4 Openn grassland !! >500 ! 5 5
Tablee 2.8. Scoring of soil moisture, percentage of area grazed and cover by various grass species s
Soill Moisture Score e Grazingg Intensity jj Score Grasss species cover || Code Dryy (dry sites) :: 1 Loww <25% jj 1 0-<5% % 11 ° Moistt (damp sites) 11 2 Modd 25-50% || 2 >5-<25% % || 1
3 || 2 Wett (waterlogged sites) !! Heavyy 50-90% || 3 >25-<75% % >75% % || 3
20 0 STUDYY AREAS AND METHODS
2.2.4.. SITES, TRANSECTS, SECTIONS Grasslandd bird communities and environmental variables were recorded along 59 transects in the threee protected areas between January 1996 and May 1998. Each 100 m of a transect is termed a section.. All records of birds were used for the general chapters (1, 2, 3, 4 and 8). For the rigorouss statistical analysis presented in chapters 5, 6 and 7 a selection was made of records assembledd in transect sections visited at least 5 times in one of the four sampling seasons: Dec 96 - Febb 97 (W97), Mar 97- May97 (S97), Dec 97- Feb 98 (W98), Mar 98 - Jun 98 (S98). A description off how this number of 5 visits was chosen is given in Chapter 4. For each section, the 5 survey visitss were combined to give a robust estimate of bird population size and structure. This combinationn of 5 visits to a section is referred to as a site. In all, 43 sites were surveyed during one seasonn only, 43 during two seasons, 41 during three and 40 during all four seasons; giving a total of 4122 sites. For sections surveyed on more than 5 occasions in each season, population estimates weree derived from 5 surveys selected at random. Since no transects in Koshi Tappu were visited 5 timess in one season, these were removed from the ordination and classification analysis.
2.2.5.. DESCRIPTION OF GRASSLAND TYPES AA great number of grass assemblages have been described for Nepal's grasslands, corresponding to variouss combinations of environmental variables (Table 2.9). The distribution of the grassland types inn reserves was somewhat uneven. While Sukila Phanta was dominated by short grass species, the Chitwann grasslands were dominated by the taller Saccharum and Narenga assemblages (Peet 1997, Peett et al. 1999). Distribution of the sampled grassland habitat is presented in Table 3.1 and for the 4122 sites in the 5-visit data set in Tables 5.5 and 5.6.
2.2.6.. IDENTIFYING GRASSLAND BIRDS Inn the Indian subcontinent, grassland birds are one of the most difficult bird groups to identify, generallyy because of their elusive nature and similarity to each other (Fleming et al. 1984, Inskipp andd Inskipp 1991). To overcome this, thorough practice was needed to enhance knowledge of the identificationn and vocalisations of grassland birds. My previous work experience in Chitwan as a naturalistt guide helped a great deal in this regard. Furthermore several local field birders were consultedd and a fair amount of time was spent with them in lowland grasslands. Knowledgeable guidess also accompanied me in the field to cross-check any errors.
Severall ornithologists provided tape recordings of grassland birds to enhance my knowledge on vocalisationss of grassland birds. When confusion arose several playback experiments carried out to testt bird identifications. Well-planned and thorough practice contributed to a good set of bird data collectedd at species level. More than 90% of the birds recorded were identified to species level in the field. field.
21 1 STUDYY AREAS AND METHODS
Tablee 2.9. Grassland types recognized, mainly corresponding to similarly named assemblagess in Peet et al. (1999).
Cymbopogonn grassland. jj A grassland where Cymbopogon sp. is the dominant !! grass type(>50 to 75%). Sward height roughly 2 m, || growing at the edge of sal forests. Imperata-Narengaa grassland. || A grassland where Imperata is dominant with \\ Narenga porphyrocoma as codominant. Imperata 1 ;; ra tall, Narenga >4 m tall. Imperataa grassland. jAA short grassland where Imperata cylindrica is 'dominantt (>75%). Narengaa grassland. !! A grassland where Narenga porphyrocoma is II dominant. Sward height always >4 m. A widespread ii grassland type in Chitwan. Phragmites-Saccharumm grassland. ;; A grassland with Phragmites karka seemingly ii dominant from 25% to 75%. Saccharum \arundinaceum\arundinaceum and Saccharum spontaneum are the || codominant species. Sward height >4 m. Saccharumm grassland. IAA grassland where Saccharum spontaneum is the jj dominant grass species. This grassland is mainly jj found along the recently flooded alluvial plains or in [abandonedd village sites. Sward height 2 m. Saccharum-emergentt grassland. !AA grassland where Saccharum bengalense is the jj dominant grass species with Saccharum spontaneum \\ and several woody species as the codominants. The ;; dominant woody species are Artemisia vulgaris, \Clerodendron\Clerodendron viscosum, Colebrookia oppositifolia. jitt is also characterised by moderate digging by the [wildd animals..Not well defined in Peet et al. (1999). Themedaa grassland. jj A grassland growing at the edge of sal forest or mixed II forest. An extensive grassland in Chitwan where ;; Themeda arundinacea was the dominant and Apluda \mutica\mutica the codominant grass species. The sward jj height >4 m. Tall Themeda arundinacea was seen jj bending down horizontally to the ground with jj advancing age. Wheatt grassland. jj A grassland site previously dominated by Imperata- \Narenga\Narenga grassland. It is one of the managed [grasslandss where grass and a few woody species jweree removed manually, then ploughed. Wheat was [sownn to attract herbivores. Sward height <.5 m. Not !! identified in Peet et al. 1999. Forestt grassland. jj Grasses growing as the dominant vegetation under II forests. Most of these sites sampled were in sal jj forests. Sward height 1.5 m. Not identified in Peet et lal.lal. 1999.
22 2 STUDYY AREAS AND METHODS
2.2.7.. DATA COLLECTION TIME Duringg the first year of the study in early 1996, I carried out several repeat visits in a single day withinn the same transect to find out the daily variation in activity pattern of birds. This revealed a considerablee variation in the number of birds seen or heard during different times of the day. Diurnal variationn in bird activities and song was greater in the hotter months (March, April and May) than inn the cooler months (December, January and February). Considerably higher bird activities occurred inn the morning compared to the afternoon (Figure 2.3). This observation is probably true for all tropicall and subtropical grasslands of the world whereas in temperate grasslands little variation in grasslandd bird singing rates with time of day have been observed (Kantrud and Kologiski 1983). In laterr years, bird data were collected between 0600-1100 hrs and again between 1400-1900 hrs in orderr to record the maximum number of species within the sample site. The very first and last roundss of observations depending upon the amount of sunlight. As it lies to the west, sunlight lasted almostt 30 minutes longer in Sukila Phanta than in Chitwan
Figuree 2.3. Diurnal variation in bird activities, (transect 2, Chitwan during 1996-1998)
23 3 STUDYY AREAS AND METHODS
2.2.8.. BIRD CENSUSES Forr each visit a data sheet (Appendix 2) was completed in which all bird observations were recorded.. The exact distance along transect and the distance to the right or left of transect were noted (Bibbyy et al. 1992) for all birds observed. On the bird data sheet the following details about the observedd birds were noted: species, number, sex, location, behaviour and the overall height of the vegetationn used by the birds. All birds below 10 metres (including those flying) were recorded. Only birdss positively identified at the species level were registered and used for final analysis. Bird censusess were not carried out on rainy, strongly windy, totally overcast and cloudy days to avoid biasess due to the change in intensity of bird activities.
2.3.. Data Analysis Thee assembled data were stored in a Microsoft Excel spreadsheet. All variables requiring transformationn to give approximate normality were log transformed (ln(n+l)) prior to other statisticall assessment. This applied to both the habitat variables and biological variables. As there wass a difference between data collected before (December-February, 'winter') and during the breedingg season (March-June, 'summer'), summer and winter data were analysed separately. Based onn this study and further consultation with experts, Pale-footed Bush Warbler Cettia pallidipes and White-tailedd Stonechat Saxicola leucura were identified as nationally threatened species because of theirr specific habitat requirements, habitat loss and restricted distribution.
2.3.1.. ORDINATION Ordinationn is a mathematical treatment which allows samples to be organised in such a way that thosee that are most similar in bird species composition and relative abundance will appear closest together,, while samples which differ greatly in the relative importance of a similar set of species, or whichh possess quite different species, appear far apart (Begon et al 1990). Ordination analysis of thee bird data was done using CANOCO for Windows (Ter Braak and Smilauer 1998). Ordination axess can then be related to environmental data to reveal potential influences on organism distribution,, though in practice these relationships are correlative and hence provide no evidence aboutt cause and effect.
2.3.1.1.. Detrended correspondence analysis (DCA) Detrendedd Correspondence Analysis (DCA, Hill and Gauch 1980) was used to identify the main patternss of bird species relative to the habitat data. DCA is an indirect gradient technique that assumess a unimodal response of species to their environment and provides a robust ordination techniquee for data that have a large number of taxa and many zero values (Ter Braak and Prentice 1988,, Kent and Cocker 1992). The sample scores are calculated as weighted averages of the species scoress and the scores are standardised such that the within-site variance is equal to 1 (Ter Braak 1996). .
24 4 STUDYY AREAS AND METHODS
2.3.1.2.. Canonical correspondence analysis (CCA) Canonicall Correspondence Analysis (CCA) was used to directly relate variations in the occurrence andd abundance of bird species between sites to variables describing the physical characteristics of sites.. CCA is direct gradient technique that arranges sites sequentially based on major trends in speciess composition and abundance. CCA seeks to explain changes in community structure that are directlyy related to environmental gradients by assuming a unimodal response of biological communitiess to their environment (Jongman et al. 1995). In CCA, the occurrence and abundance of speciess (or taxa) in space and time are related to linear combinations of environmental variables that explainn the greatest variation in the species data. In this analysis rare species are 'downweighted' to minimisee their influence and reduce the risk of chance associations that can confuse real trends. CCAA was carried out using CANOCO version 4.0 (ter Braak and Smilauer 1998). The first step was too identify environmental variables that explained a statistically significant proportion of the variationn in the bird data for inclusion in CCA. This is a stepwise procedure that tests the significancee of individual variables, starting with the variable explaining the greatest variance, before includingg it in the model. Forward selection was used to identify environmental variables for inclusionn in ordination, which each explained a statistically significant proportion of the variation in thee bird data. Forward selection ended once the inclusion of an addition environmental variable no longerr explained a significant proportion of the variation in bird communities. Each environmental variablee was tested for significance using Monte Carlo permutation test (999 permutations; Verdonschott and ter Braak 1994). Forward selection was used to partition the explained biological variancee between the environmental variables.
Thesee results are summarised by the ordination diagram (chapter 6), in which, the axes represent variationn in invertebrate communities and the arrows represent environmental variables. The environmentall variables point in the direction of maximum change, with the lengths of the arrows reflectingg the magnitude of change in that direction. Environmental variables with long arrows were moree strongly correlated with ordination axes and were also more closely related to patterns of invertebratee variation than variables with short arrows (ter Braak 1996).
2.3.2.. TWINSPAN CLASSIFICATION Classificationn analysis was carried out using the polythetic divisive clustering technique based on birdd and habitat data using Two-way Indicator Species Analysis (TWINSPAN) (Hill 1979). This is thee most widely used technique for polythetic divisive classification (Kent and Cocker 1992). Pseudo-speciess cut levels were set at 1, 5, 10, 20 and 50 of the bird abundance values, whilst all otherr options were set to default levels. The groups resulting from the TWINSPAN analysis are describedd in Chapter 5 by including only indicator species and strongly preferential species for each groupp to avoid producing long lists of species.
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2.3.3.. ANALYSIS OF VARIANCE (ANOVA) Differencess in species richness and abundance between sites categorised on different habitat characteristicss were assessed by one-way ANOVA. DCA and CCA scores were used to compare thee means of different grassland types.
2.4.. Nomenclature Birdd names follow Inskipp, T. P., Lindsey, N. and Duckworth, W. (1996): An annotated checklist of thethe birds of the Oriental region. Oriental Bird Club, UK. Taxonomy followed by this book is based onn Sibley and Monroe (1990, 1993). The common name and scientific name are mentioned on the firstt mentioning of a bird thereafter only the scientific name is mentioned.
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