Turkish Journal of Zoology Turk J Zool (2020) 44: 424-439 http://journals.tubitak.gov.tr/zoology/ © TÜBİTAK Research Article doi:10.3906/zoo-2003-23

Diurnal time-activity budget and foraging techniques of red-crested pochards (Netta rufina) wintering at the wetlands of West Bengal, India

1,2 2, 2 Arkajyoti MUKHERJEE , Sudin PAL *, Subhra Kumar MUKHOPADHYAY  1 Department of Chemical Engineering, Jadavpur University, Kolkata, India 2 Ecotechnology Project Laboratory, Government College of Engineering and Leather Technology, Kolkata, India

Received: 16.03.2020 Accepted/Published Online: 09.08.2020 Final Version: 14.09.2020

Abstract: The present study aimed at recording the time-activity budget and feeding techniques of red-crested pochards (RCPs) to test the hypotheses that feeding techniques were influenced by the sexes and contrasting physical conditions of the habitat. The time- activity budget was quantified using the scanned sample approach. In this study, the mean sex ratio of the RCPs was recorded as 0.655. Dominant behavior was sleeping or resting (42.8% in February to 47.0% in January), followed by swimming (27.1% in February to 29.8% in December), feeding (10.9% in December to 16.6% in February), and preening (9.0% in January to 12.1% in February). During the diurnal hours, resting was highest in the morning, while swimming and feeding were both highest midday. Climatic factors, such as the maximum and minimum air temperatures, maximum and minimum air temperature differences, and day length, were considered to be influential on the diurnal time activities of the RCPs. Male were more frequent divers than the females and the duration of diving was greater in males than in females. However, in shallow water, beak dipping and upending were major foraging techniques in both sexes. The depth of the water played a significant role in the selection of the feeding techniques.

Key words: Red-crested pochard, diurnal behavior, foraging technique, migratory waterbird, time-activity budget, wintering

1. Introduction individuals that differ consistently in their food choices and Wetland birds, like red-crested pochards (RCPs), Netta foraging techniques (Van Donk et al., 2019). In the present rufina, that migrate southwards along the East Asian- study, focus was placed on the diurnal time-activity budget Australasian flyway (EAAF) through tropical areas of RCPs, a Palearctic species that breeds locally across continue storing fat reserves before leaving for colder southern and central Europe to the west and central Asia. regions of breeding sites at higher latitudes (Morrier The breeding distribution of RCPs extends across Eurasia and McNeil, 1991). Migrants of the EAFF must forage from Mongolia to Portugal between the latitudes of 35°N when 1) replenishing at a stop-over site after a long over- and 55°N. A great deal of data has been recorded on the Himalayas flight, 2) molting, and 3) accumulating fat in Black Sea and eastern Mediterranean wintering group and preparation for long migration crossing the Himalayas the central European/western Mediterranean wintering towards their breeding sites. The distribution of time in groups (Delany and Scott, 2002). However, information different activities in the day time, including foraging, on the south Asia wintering group is limited (Delany et varies among waterbird species and individuals (Draidi al., 2006). RCPs winter from Afghanistan to India and et al., 2019). Time allocations for different daily activities southern China, and are a high-flying winter visitor to the surely have important implications for meeting the energy whole Indian subcontinent. This is categorized as least requirements of the concerned species. The physical concern (LC) on the International Union for Conservation habitat, social organization, and environmental conditions of Nature (IUCN) Red List (BirdLife International, of the individual species can be accessed from extensive 2019b); however, its population trend is unknown. Being a time-activity budget studies (Paulus, 1988; Datta, 2014). migratory species, it is protected under the Convention on Wintering strategies, feeding techniques, habitat use the Conservation of Migratory Species of Wild patterns, niche sharing, and resource partitioning can also or Convention on Migratory Species (Bonn Convention) be comprehensively commented on from such studies under the United Nations Environment Program and (Aissaoui et al., 2011; Ali et al., 2016). Populations consist of Wildlife and Countryside Act, 1981. * Correspondence: [email protected] 424

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RCPs are predominantly herbivores and have been bandh (Site 2: 23.203173°N, 86.220509°E), the other reported as a diurnal species (Carboneras and Kirwan, wetland located in Purulia District, although facing 2019). Amat (2000) reported that RCPs collect submerged pollution through municipal wastewater inputs and macrophytes underwater and bring the plants to the anthropogenic pressures, which has led to degradation of surface to eat. Their vegetative diet is often supplemented the habitat quality, it shelters a sizable population of RCPs. for protein with aquatic insects and their larvae, Kadamdeuli Dam (Site 3: 23.061327°N, 86.514213°E) and crustaceans, snails, amphibians, and small fish (Amat, Gangdoa Dam (Site 4: 23.243186°N, 87.052518°E) are 2000). RCPs usually forage employing 3 main techniques, located on the Shilabati River and Shali River, respectively, such as diving, up-ending, or dabbling, depending on in Bankura District; these far-flung locations make these the availability of the types of aquatic macrophytes and sites suitable wintering grounds for migrating waterbirds. depth of the water. However, they do favor rather deep, At 3 of the study sites, namely, Sites 1, 2, and 4, no large lakes and lagoons of fresh or brackish waters with appreciable waterlevel fluctuations were recorded during abundant fringing (Kear, 2005; Carboneras and Kirwan, the study period. At these sites, the water depth was never 2019). Amat (1984) compared the habitat use of RCPs below 1.5 m. However, Site 3 showed a drastic decrease and common pochards in winter and spring. The time- in water depth from the end of December; in January, the activity budgets of common pochards (Green, 1998a; Ali mean depth fell to 0.9 ± 0.6 m due to rapid drainage of the et al., 2016) and ferruginous ducks (Sabir, 2004; Draidi et water (nearly 80% reduction in the mean depth). Figure al., 2019) have been studied. Although the time-activity 1 shows the location map and further description of the budgets of several other wetland ducks (Green et al., study sites are elaborated on Table 1. 1998a; Das et al., 2011; Ali et al., 2016; Saker et al., 2016) 2.2. Observations of the birds and shorebirds (Morrier and McNeil, 1991; Marteinson 2.2.1. Population estimation et al., 2015) are on record, such studies on RCPs are For population estimation, all sides of each of the 4 wetlands altogether absent. The only report on the behavior of a were surveyed from October 2018 through March 2019 hybrid of RCPs (Netta rufina × Aythyanyroca) was made (however, RCPs were present from November through by Randler (2003). Extensive information on the time- March), by walking along a transect length of 1km and activity budget of an individual species would focus on the counting the number of RCPs seen in water within 50 m of conditions of the physical habitat and social organization the transect path, using a TruePlus 360 Laser range finder (Paulus, 1988; Datta, 2014). The time-activity budget (Laser Technology, Inc., CO, USA) and Olympus (8 × 40 could also comprehensively point out the strategies for the DPS I) binoculars (Tokyo, Japan). October through March use of feeding techniques, habitat use, niche sharing, and was considered the best period for studying wintering, resource partitioning (Aissaoui et al., 2011; Datta, 2014). as well as resident birds in southern Asian countries In the present work, the time-activity budget and foraging (Mazumdaret al., 2007; Chatterjeeet al., 2020). Two field techniques of RCPs in their natural wintering habitats was observations were conducted, one each in the second and recorded to understand their habitat use, and diurnal and last week of each month, and the counts were made along seasonal changes in the time-activity during wintering line transects (Huttoet al., 1986; Bibbyet al., 1992; Buckland period. To our knowledge, this was the first attempt to et al., 1993), by 2 trained observers, separately, at 3 specific examine the diurnal time-activity of wintering RCPs in time intervals (6:00–7:00 AM, 12:00–1:00 PM, and 4:00– the Indian subcontinent. The present work tested 3 main 5:00 PM). The raw count data of all of the measures were hypotheses: 1) time investment in foraging is never highest averaged month-wise to obtain representative data and for diurnal activities; 2) there exist sex-wise differences in used as the population size (Gibbons and Gregory, 2006). employing the foraging techniques, and 3) the physical The occurrence of males and females at each of the 4 study habitat (here depth) can influence the time invested in a sites was noted during the study period. The sex ratio was particular foraging technique. expressed as the proportion of males within the sample (Brides et al., 2017; Frew et al., 2018). The sex ratio was 2. Materials and methods calculated as: sex ratio = nm/ (nm + nf), where nm and 2.1. Study areas nf refer to the total number of males and total number of Selected were 4 study sites that consistently shelter females, respectively (Brides et al., 2017). populations of wintering RCPs in West Bengal (in the 2.2.2. Behavioral categories districts of Purulia and Bankura), India. Adra Saheb Behavioral categories were recorded as (Green et al., bandh (Site 1: 23.285692°N, 86.423444°E) harbors a good 1998a): feeding (diving and the interval between 2 number of winter avian species; timely water hyacinth dives); resting (including sleeping behaviors without management and proper protection make it a suitable head-on-back and with head-on-back, and eyes open or wintering habitat for avian migrants. Purulia Saheb closed, loafing); preening (including comfort, bathing,

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Figure 1. Study site (Adra saheb bandh,Purulia saheb bandh, Kadamdeuli Dam, and Gangdoa Dam) locations inWest Bengal, India (India and West Bengal maps not in scale). wing-flapping, wing-shaking, head-shaking, stretching); • Upending: Upending or tipping is a feeding technique swimming (including searching/scanning, and flying); where the bird partially submerges in a vertical position others (including alert, and intra- and interspecific while foraging with its tail and legs above the water surface. social interactions). Feeding behaviors were additionally • Diving: The bird temporarily vanishes underwater to subcategorized on the foraging techniques used by the forage. RCPs. The following 5 categories were identified from 2.2.3. Recording time-activity previous studies (Liordos 2010; Peŕez-Crespo et al., For observations on the time-activity budget, a total period 2013), which were used herein while categorizing the field of 32 days (2 days per wetland per month from November observations of the feeding behavior of the RCPs: 2018 through February 2019) was invested. Only the • Beak dipping: When the birds forage by dipping the first observation on each individual RCP was taken into beak, partly or in full, into the water. consideration (initial observation method of Liordos, • Head dipping: When the birds forage by dipping the 2010) and the scan sampling (Martin and Bateson, 1993) head, including the beak, in water. In this case, the eyes too technique was employed from representative visual points are underwater while foraging. at each site that were opportunistically chosen because • Neck dipping: This foraging technique includes of their accessibility and unhindered yet secretive view, dipping up to the neck in water, fully or partly at the using Olympus (8 × 40 DPS I) binoculars and a Sony foraging site. RX10 IV camera (Tokyo, Japan). For ad libitum binocular

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Table1. Descriptions of the 4 study sites.

No Sites Location Description

Shore length: 7.98 km, area: 76 ha, altitude: 166 msl, mean depth: 3.5 m. A natural 23.285692°N, wetland in Purulia District, surrounded by Kang forest. Timely water hyacinth Site 1 Adra Saheb bandh 86.423444°E management and proper protection by the Indian Railway Department make this habitat suitable for winter avian fauna.

Shore length: 2.87 km, area: 31.3 ha, altitude: 250 msl, mean depth: 2.5 m. A manmade lake governed by Purulia Municipality. Wastewater input, plastic 23.203173°N, Site 2 Purulia Saheb bandh and thermocol load, different anthropogenic activities, tourism, and land use 86.220509°E change (urbanization) in the surrounding area are major reasons for the habitat degradation at this site.

Shore length: 5.26 km, area: 38 ha, altitude: 116 msl, mean depth: 4.5 m. Located 23.061327°N, in Bankura District and is a dam area of Shilabati River, where a canal from the Site 3 Kadamdeuli dam 86.514213°E Mukutmanipur-Kangsabati dam meets. The area is mainly surrounded by bushes and patch forest; however, barren lateritic land also presents.

Shore length: 9.24 km, area: 92.7 ha, altitude: 108 msl, mean depth: 7.5 m. A 23.243186°N, reservoir of Shali River located in Bankura District. This area is mostly Site 4 Gangdoa Dam 87.052518°E surrounded by agricultural land, but fishing and illegal hunting creates pressure on this wetland.

observations and video recordings, 3 random durations of repeated observations of the same RCP individual. The 30 min, within four 2-h 45-min time durations, between time-activity budget was quantified using the scan-sample 06:00 AM and 05:00 PM, on each sampling day, were approach (Losito et al., 1989). While employing the devoted from 4 to 8 vantage point, depending on the area instantaneous or scan-sampling method (Altmann, 1974), of the wetlands, to scan all of the details of the behaviors the behaviors of all of the individuals in a group were of the species in the field. Altogether, 32 observations, recorded at predetermined time intervals (30 s) during the spending a total of 96 h, were gathered during the presence selected diurnal hours. of RCPs over 4 months of wintering and the mean values 2.3. Macroclimatic conditions in percentages were represented. Mean monthly average conditions of the prevailing 2.2.4. Recording foraging behavior macroclimate, such as maximum and minimum air Recorded were 5 foraging techniques, employed temperatures (maxtemp and mintemp), differences separately by female and male RCPs, at each study site between the maximum and minimum temperatures, (6 observations covering 18 h) during 2 of the wintering sunrise, sunset, day-length, solar irradiance, cloud cover, months (December and January). This study aimed to rainfall days, amount of rainfall, and relative humidity record the sex-wise and depth-wise differences in the were collected from authentic weather record websites foraging techniques, if any. One of the study sites, Site 3, and are depicted in Annexure I. As the distance between which experienced a drastic decrease in water depth in the sampling sites varied from 46.6 km to 90.9 km, spatial January, provided the opportunity to study the effect of changes in the macroclimatic conditions were ruled out. water depth on the foraging behaviors of RCPs. The mean 2.4. Statistical analysis values in percentages were used for the statistical analyses. Principal component analysis (PCA) with Kaiser Video recordings alongside binocular observations were normalization and Varimax rotation was performed on analyzed for the behavioral patterns of RCPs. Focal the dataset for macroclimatic factors. The factor loadings subgroups of 10–20 RCPs were selected for observation (FLs) given by PCA for the first principal component were of foraging behavior in each survey time. The focal study taken into account. Whether the loading was positive or groups were selected based on the closest readily visible negative, factors with loading magnitudes of more than groups of individuals. The potential problem of sample 0.8 were loaded on the latent component and considered nonindependence for performing different sampling to be key influences on the RCP population. Canonical sessions at the same site was avoided by carefully shunning correspondence analysis (CCA) is a multivariate

427 MUKHERJEE et al. / Turk J Zool method that is applied to unravel the relationships Sites 1, 3, and 4. The highest number of individuals was between biological assemblages and their environments in December at Site 3, while it was in February at Site 4. (terBraak, 1994; terBraak and Verdonschot, 1995). In At Site 3, following the fast decrease in water depth within the present study, CCA was employed to relate the site- a week, a substantial decrease in the population of RCPs wise and month-wise population density of the RCPs to (nearly 64%) was recorded in January. However, at the the macroclimatic factors (shortlisted with PCA). One- other sites, the population of RCPs markedly declined in way analysis of variance (ANOVA) was performed with March, the usual time of emigration (Annexure II). The statistical significance accepted as P ≤ 0.05, and calculated projections in the CCA plots were constructed using partial ŋ2 for the effect size to determine whether the the data obtained on the month-wise and site-wise RCP foraging techniques differed between the habitats and density together with select climatic factors obtained from sexes (Kabasakal et al., 2017). ANOVA was followed by the PCA results (Figure 2). Like many other ducks, RCPs post hoc Tukey HSD tests to determine the mean values are sexually dimorphic, and thus determining the sex that differed significantly (Pal et al., 2018). Pearson ratio becomes easier. At the present study sites, the RCP correlation coefficient values (P < 0.05 indicatedstatistical populations were mainly male-dominated (Table 2) and significance) betweenthe density, time-activity, and PCA a similar situation prevailed throughout the wintering selected climatic factors were calculated. All means were period. No definite changes in the sex ratio were observed shown with ± standard deviation. Statistica9.0 (StatSoft, at the study sites during the study period. The average adult Inc., Tulsa, OK, USA) and PAST3.0 software packages were sex ratio, considering all of the sites, was 0.655 ± 0.138. used for the statistical analyses. Graphical representations 3.2. Diurnal time-activity budget were generated using Origin 2016 (OriginLab Corp., Figure 3 depicts the percentage of time allocated by the Northampton, MA, USA). RCPs for different activities during the day. Resting, including sleeping, was the major diurnal activity (ranging 3. Results from 42.8% in February to 47.0% in January) of the RCPs. 3.1. Population density and sex ratio Other major diurnal activities were swimming (ranging During the present study, the first appearance of RCPs from 27.1% in February to 29.8% in December), followed was recorded at Site 2 in November (Annexure II). by feeding (ranging from 10.9% in December to 16.6% in After November, the density of RCPs increased and was February) and preening (ranging from 9.0% in January to highest in January at Site 2. This site maintained a fairly 12.1% in February). A trivial percentage (ranging from similar number of individuals from December through 1.6% in February to 4.2% in January) of the total diurnal February, which suddenly dropped to a minimum in time was allotted to all other minor activities, such as alert, March. However, the density of RCPs was much higher at and intra- and interspecific social interactions. Around Site 1 when compared to the other 3 sites and the highest 27% of the time allocated for swimming was allotted to mean number, as high as 431.5 (SD ± 19.93) individuals, searching/scanning and short stint flights throughout the was recorded in January. RCPs arrived in December at study period. The time allocated for resting, swimming,

Figure 2. Canonical correspondence analysis (CCA with 95% ellipses) ordination diagram showing the scatter plot for the month-wise and site-wise density of the wintering RCPs together with the selected environmental variables. Vector lines represent the relationship of significant environmental variables to the ordination axes; their length is proportional to their relative significance.

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Table 2. Site-wise monthly male (M) and female (F) density and sex ratios (SRs) expressed as the proportion of males within the sample of RCPs (NR = not recorded).

Month Site 1 Site 2 Site 3 Site 4

M:F SR M:F SR M:F SR M:F SR Nov 2018 NR NR 11:7 0.611 NR NR NR NR Dec 2018 121:65 0.651 37:30 0.552 53:31 0631 8:7 0.533 Jan 2019 259:173 0.599 33:32 0.508 20:10 0.666 50:30 0.625 Feb 2019 82:42 0.661 31:21 0.596 15:7 0.681 60:41 0.594 Mar 2019 NR NR 4:3 0.571 2:0 1.000 1:0 1.000

Figure 3. Month-wise and time-wise proportional time budget of the RCPs. Values are given in percentages of the time spent in the diurnal activities (mean value ± SD; n = 32; 96-h observation).

429 MUKHERJEE et al. / Turk J Zool and foraging varied from November through February. A 3.3. Foraging techniques in males and females considerable variation in the time allocated for foraging 3.3.1. Techniques in deep water activity was recorded during the study period (an increase Deep-water conditions (mean depth always >1.5 m) in foraging time by around 52% between December and prevailed throughout the study period at Sites 1, 2, and February). The time allocated for resting was highest in 4, and at Site 3 until the end of December. Under deep the morning, i.e. 6:00–8:45 AM (ranging from 79.5% in water conditions, the percentage of time allotted to diving February to 90.0% in January), whileit was lowest during in the case of male individuals (ranging from 78.8 ± 0.55 midday, i.e. 11:30 AM–2:15 PM (ranging from 11.5% in at Site 4 in December to 82.6 ± 0.42 at Site 2 in January) February to 16.0% in December). However, the allocation was significantly higher than that of females (ranging from of time for swimming was highest midday, i.e. 11:30 58.1 ± 2.11 at Site 4 in December to 61.2 ± 1.20 at Site AM–2:15 PM (ranging from 37.5% in February to 42% 2 in December). This was noted at all of the study sites in November), while it was lowest in the morning, i.e. (Figure 4). However, the percentage of time allotted to 6:00–8:45 AM (ranging from 5.1% in December to 10.5% beak dipping by females (ranging from 32.4 ± 0.21 at Site 2 in February) throughout the study period. Likewise, the in January to 35.0 ± 1.87 at Site 4 in December) was much allocation of time for foraging was highest midday, i.e. higher than in male individuals (ranging from 11.2 ± 0.69 11:30 AM–2:15 PM (ranging from 19.9% in December, at Site 1 in December to 13.2 ± 0.95 at Site 4 in December). to as high as 33.1% in February), while it was lowest in It was observed that the RCPs were predominantly divers the morning, i.e. 6:00–8:45 AM (ranging from 0.9% in in deeper water habitats (ranging from 69.2 ± 11.11 at Site 4 December to 2.0% in February). Significant (P < 0.05) to 71.6 ± 11.08 at Site 2), followed by beak dipping (ranging negative correlation coefficients (Table 3) were noted from 21.9 ± 11.28 at Site 2 to 23.3 ± 12.57 at Site 4).During for foraging with swimming (r = –0.850) and resting 10-min ad libitum observations, while 4–5 diveswere (r =–0.775). An increase in preening activity from late recorded for males, 2–3 dives were recorded for females. morning, i.e. 8:45–11:30 AM, through the afternoon, Time spans of the diveswere 10.9 ± 3.0 s for males and 8.3 i.e. 2:15–5:00 PM, was prominent. Preening showed a ± 2.4 s for females during the peak hours of feeding, i.e. significant negative correlation with resting (r = –0.776). 12:00–3:00 PM, at all 4 study sites. A significant difference Time allocations for other different activities, such as alert, (ANOVA: F = 30.88; P < 0.001; partial ŋ2 = 0.347; n = 60) and intra- and interspecific social interactions, were also was noted between the males and females with regards highest midday, i.e. 11:30 AM–2:15 PM (ranging from 3% to their preferred foraging techniques in deeper waters. in February to 7.9% in January). Other activities showed Significant mean differences in the different foraging significant negative correlations with preening (r = –0.937) techniques used by the male and female RCPsat Sites 1, and foraging (r = –0.656), while a significant positive 2, and 4 were also noted in the post hoc analysis (Table correlation was found with resting (r = 0.738). 4a). The RCPs were basically divers and thereby, foraging

Table 3. Pearson correlation coefficients between the selected climatic factors, time allocated to different diurnal time activities, and RCP population densities at the study sites (marked correlations were significant at P < 0.05; n = 16).

Max temperature Min Min temperature 0.758* temperature TD –0.229 –0.809* TD DL 0.810* 0.847* –0.532* DL Resting –0.310 –0.714* 0.786* –0.794* Resting Swimming –0.419 –0.059 –0.290 –0.578* 0.332 Swimming Feeding 0.517* 0.484 –0.256 0.862* –0.775* –0.850* Feeding Preening –0.353 0.167 –0.568* 0.257 –0.776* –0.124 0.467 Preening Other Other activities 0.271 –0.054 0.325 –0.329 0.738* 0.444 –0.656* –0.937* activities RCP density –0.609* –0.264 –0.155 –0.727* 0.410 0.974* –0.891* –0.066 0.358

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Figure 4. Comparison of the aggregated proportional time budget (values in percentages of the time spent) of the diurnal foraging activities of male and female RCPs in January and December; deep water conditions prevailed in both December and January at Sites 1, 2, and 4, while shallow water conditions prevailed at Site 3 in January. by diving was significantly different from other foraging ± 0.5 m high above the bottom. A contrasting picture in techniques in deeper water. This was also true for the RCPs using foraging techniques was apparent (Figure 4) when at Site 3 in December (Table 4b). the techniques were compared between December (deeper 3.3.2. Techniques in shallow water water habitat) and January (shallow water habitat). A Site 3 providedan ideal situation to compare the changes significant difference in the preferred foraging techniques in foraging techniques employed by the males and females (ANOVA: F = 12.46; P = 0.0024; partial ŋ2 = 0.41; n = in shallow water (mean depth of 0.9 ± 0.6m in January). 20) was noted between the deeper and in shallow water Site 3, at the Kadam Deuli Dam, is a reservoir where a habitat conditions. As mentioned, both the male and canal from the Mukutmanipur Kangsabati Dam meets female RCPs were predominantly divers (percentage of the Shilabati River. Water of the reservoir was usually time allotted was 70.4 ± 11.68) in deeper water habitats drained at the onset of a drier period for irrigation and (in December), followed by beak dipping (23.1 ± 11.90). processing for drinking water supply of drought-prone However, under shallow water conditions during January, Bankura District of West Bengal, India. The dominant foraging by beak dipping was highest (50.4 ± 1.18 for submerged hydrophyte in this study site was Waterthyme males and 60.8 ± 1.90 for females), followed by upending (Hydrilla verticillate), which stood on an average of 0.8 (30.5 ± 1.63 for males and 23.6 ± 0.99 for females). Under

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Table 4a. Multiple comparisons of the significant differences in the foraging techniquesby male and female RCPs in both December and January with deeper water habitats (at Sites 1, 2, and 4) using post hoc analysis with Tukey HSD (*differences were significant at P < 0.05).

Foraging Foraging Mean Foraging Foraging Mean Sites 1,2, and 4 Sites 1,2, and 4 techniques (I) techniques (J) difference (I–J) techniques (I) techniques (J) difference (I–J) Beak dipping 69.02* Beak dipping 69.90* Head dipping 79.26* Head dipping 80.00* Diving Diving Upending 75.30* Upending 76.05* Neck dipping 80.85* Neck dipping 81.46* Diving –69.02* Diving –69.90* Head dipping 10.24* Head dipping 10.10* Beak dipping Beak dipping Upending 6.28* Upending 6.15* Neck dipping 11.83* Neck dipping 11.56* Diving –79.26* Diving –80.00* Males in Males in December Beak dipping –10.24* January Beak dipping –10.10* Head dipping Head dipping (with deeper Upending –3.96* (with deeper Upending –3.95* water >1.5 m) water >1.5 m) Neck dipping 1.59 Neck dipping 1.46 Diving –75.30* Diving –76.05* Beak dipping –6.280* Beak dipping –6.15* Upending Upending Head dipping 3.96* Head dipping 3.95* Neck dipping 5.55* Neck dipping 5.41* Diving –80.85* Diving –81.46* Beak dipping –11.83* Beak dipping –11.56* Neck dipping Neck dipping Head dipping –1.59 Head dipping –1.46 Upending –5.55* Upending –5.41* Beak dipping 26.32* Beak dipping 27.78* Head dipping 55.25* Head dipping 55.56* Diving Diving Upending 58.12* Upending 58.63* Neck dipping 59.80* Neck dipping 60.43* Diving –26.32* Diving 27.78* Head dipping 28.93* Head dipping 55.56* Beak dipping Beak dipping Upending 31.80* Upending 58.63* Neck dipping 33.47* Neck dipping 60.43*

Females in Diving –55.25* Females in Diving 27.78* December Beak dipping –28.93* January Beak dipping 55.56* Head dipping Head dipping (with deeper Upending 2.86* (with deeper Upending 58.63* water >1.5 m) water >1.5 m) Neck dipping 4.54* Neck dipping 60.43* Diving –58.12* Diving –58.63* Beak dipping –31.80* Beak dipping –30.85* Upending Upending Head dipping –2.86* Head dipping –3.06* Neck dipping 1.67 Neck dipping 1.80* Diving –59.80* Diving –60.43* Beak dipping –33.47* Beak dipping –32.65* Neck dipping Neck dipping Head dipping –4.54* Head dipping –4.86* Upending –1.67 Upending –1.80*

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Table 4b. Multiple comparisons of the significant differences in the foraging techniques by male and female RCPs in December with deeper water habitats and January with shallow water habitats (at Site 3) using post hoc analysis with Tukey HSD (*differences were significant at P <0.05).

Foraging Foraging Mean Foraging Foraging Mean Site 3 Site 3 techniques (I) techniques (J) difference (I–J) techniques (I) techniques (J) difference (I–J) Beak dipping 57.48* Beak dipping –19.44 Head dipping 64.70* Head dipping 12.92 Diving Diving Upending 63.20* Upending –3.48 Neck dipping 67.34* Neck dipping 19.30 Diving –57.48* Diving 19.44 Head dipping 7.22 Head dipping 32.36* Beak dipping Beak dipping Upending 5.72 Upending 15.96 Neck dipping 9.86 Neck dipping 38.75* Diving –64.70* Diving –12.92 Males in Males in December Beak dipping –7.22 January Beak dipping –32.36* Head dipping Head dipping (with deeper Upending –1.50 (with shallow Upending –16.40 water >1.5 m) water <1.5 m) Neck dipping 2.64 Neck dipping 6.39 Diving –63.20* Diving 3.48 Beak dipping -5.72 Beak dipping –15.96 Upending Upending Head dipping 1.50 Head dipping 16.40 Neck dipping 4.14 Neck dipping 22.79 Diving –67.34* Diving –19.31 Beak dipping –9.86 Beak dipping –38.75* Neck dipping Neck dipping Head dipping –2.64 Head dipping -6.39 Upending –4.14 Upending –22.79 Beak dipping 26.18* Beak dipping –29.04 Head dipping 50.46* Head dipping 13.62 Diving Diving Upending 53.44* Upending 1.00 Neck dipping 54.56* Neck dipping 16.37 Diving –26.18* Diving 29.04 Head dipping 24.28* Head dipping 42.66* Beak dipping Beak dipping Upending 27.26* Upending 30.04 Neck dipping 28.38* Neck dipping 45.41*

Females in Diving –50.46* Females in Diving –13.62 December Beak dipping –24.28* January Beak dipping –42.66* Head dipping Head dipping (with deeper Upending 2.98 (with shallow Upending –12.62 water >1.5 m) water <1.5 m) Neck dipping 4.10 Neck dipping 2.75 Diving –53.44* Diving –1.00 Beak dipping –27.26* Beak dipping –30.04 Upending Upending Head dipping –2.98 Head dipping 12.62 Neck dipping 1.12 Neck dipping 15.37 Diving –54.56* Diving –16.37 Beak dipping –28.38* Beak dipping –45.41* Neck dipping Neck dipping Head dipping –4.10 Head dipping –2.75 Upending –1.12 Upending –15.37

433 MUKHERJEE et al. / Turk J Zool shallow water conditions, diving was not a preferred 0.087 and 0.071, while the constrained eigenvalue was foraging technique for either the males or the females. No 0.258. The biplots for the site-wise and month-wise RCP significant difference in foraging by diving was recorded densities represented 55.16% and 44.84% of the variance between the males and females (values were 14.1 ± 0.47 in the climatic factors. These climatic factors, such air for males and 10.4 ± 1.41 for females), which was contrary temperatures, difference between the maximum and to the deeper water conditions at all of the sites (Tables 4a minimum temperatures, and day length were important in and 4b). Under shallow water conditions, the RCPs used influencing the RCP populations at the study sites (Figure neck dipping, which was altogether absent underdeep 2). water conditions. Under shallow water conditions during January, both sexes preferred neck dipping (2.0 ± 0.36 for 4. Discussion males and 3.1 ± 2.68 for females), alongside beak dipping Many duck and pochard species, which are widely and upending for collecting food materials. Significant distributed in the Palaearctic and migrate within the EAAF mean differences between the different foraging techniques and Central Asia Flyway, breeding in a discontinuous employed by different sexes and under the contrasting band from western Europe to western China and Inner habitat conditions of Site 3 were evident in the post hoc Mongolia, are common winter visitors on the Indian analysis (Table 4b). subcontinent (BirdLife International, 2019a, 2019b). The 3.4. Effects of climatic factors RCP is a widely distributed winter migratory species in Climatic factors, such as the maximum and minimum India, including several parts of West Bengal (Ali, 1996; air temperatures, difference between the maximum Kumar et al., 2005; Ahmed et al., 2019). As in case of and minimum air temperatures, and day length (PCA other different migratory waterbirds, RCPs appear in their component-I: FLs > 0.8) were influential on the diurnal wintering areas in India in late October and leave for their time activities of the RCPs. At the onset of winter (arrival breeding ground in late March. Madge and Burn (1988) time) and at the time approaching spring (departure time), reported that once the postbreeding moult is complete, the minimum air temperature decreased and increased, RCPs depart their breeding areas for their winter quarters, respectively, in much higher degrees than the changes in to arrive there from October/November onwards. The the maximum air temperature (Annexure I). Likewise, present work recorded a similar time frame, i.e. November the differences between the maximum and minimum to March, usual entry and exit months, respectively, temperatures were also greater during the arrival and for RCPs at the study sites herein. Changes in the day departure times of the migratory waterbirds. The day length areconsidered important environmental cues that length also started decreasing from the time of arrival of triggeravian migration (Marra et al., 2005). In the current migrant species and again increased considerably at the study, it was apparent that the higher density of RCPs was end of the wintering period. Both resting activity and observed in the lower day length period. However, the feeding activity were significantly (P < 0.05) correlated with differences in ambient air temperatures were also observed different climatic factors (Table 3). Resting was negatively to be an important cue for zugunruhe (Halkka et al., 2011; correlated with the minimum temperature (r = –0.714) Chatterjee et al., 2017). In the present study, significant and positively correlated (r = 0.786) with the difference negative correlations between the density of RCPs, and the between the maximum and minimum temperatures. maximum air temperature and day length supported the Contrarily, significant positive correlations were noted aforesaid observations. The CCA plots strongly suggested between foraging and the maximum temperature (r = that air temperature and day length significantly influenced 0.517) and day length (r = 0.862); however, the difference the RCP densities. The projections in the CCA plot showed between the maximum and minimum temperatures had that the maximum and minimum temperatures and day no significant effect on foraging. A significant negative length affected the RCP populations in November (inward correlation between the RCP population density and migration at the wintering sites) and March (outward maximum air temperature (r = –0.609) and day length migration from the wintering sites). Furthermore, at Site (r = –0.727) was recorded. terBraak (1994) reported that 3, the population size of the RCPs decreased markedly at interpretation of the angles in a canonical correspondence the end of December for a drastic decrease in water level. biplot yielded the correct sign for the correlation, but not Ma et al. (2010) also recorded similar observations on the correct magnitude, and mentioned that the canonical the effects of water level variations on population sizes of correspondence biplot was correctly interpreted via diving ducks. projection. The quality of the display could be derived from Alexander and Taylor (1983) studied the differential the eigenvalues that showed definite effects of the climatic sex distributions of several wintering diving ducks and factors on the RCP densities during the months of study at recorded that the proportion of females in the populations the 4 study sites. The eigenvalues for the first 2 axes were varied from 52% to as low as 21%. Blums and Mendis

434 MUKHERJEE et al. / Turk J Zool

(1996) reported that many diving and dabbling ducks much lower at tropical wintering sites (ranging from 25% have highly skewed adult sex ratios in favor of the to 87%) than at northern latitudes (80% to 100%). This males. Recently, Pöysä et al. (2019) reported that for the was explained by much higher energy needs for colder breeding population, the proportion of female tufted temperatures than in the tropics. Diurnal variations in ducks decreased from 42.9% (during 1951–1970) to 36.9% the feeding time were prominent during the study period. (during 1996–2015),while in the case of female common Marked diel fluctuations in the time-activity budgets pochards, these percentages were 41.8% and 39.5%, were also reported for white-headed duck, shelduck, and respectively. As reported by Pöysä et al. (2019), ‘These fulvous whistling teal (Green et al., 1998b; Boulekhssaim findings are worrying, considering that adult sex ratios are et al., 2006; Das et al., 2011; Draidi et al., 2019). Khan et al. more heavily male-biased in populations’. On average, 37% (1998) studied selected activities of nonbreeding common of the female RCPs in the populations in the present study pochards at Sarp Lake, Turkey, and recorded a negative conformed to their studies. Frew et al. (2018) reported a correlation between foraging and swimming, resting and significantly male-biased sex-ratio for pochard, pintail, swimming, and swimming and preening. The current , and shoveler. They record that the sex ratio for findings were consistent with these records. dabbling and diving ducks varied between 0.558 and 0.734. A marked seasonal variation in the diurnal time-activity In the present study, the mean sex ratio was recorded as budget was reported by Bezzalla et al. (2019). Different 0.655 for the RCPs, which was almost similar to those of environmental factors are important for influencing the the other dabblers and divers. diurnal time-activities of migratory waterbirds, which Time-activity budgets are important for focusing include temperature (Wolf and Walsberg, 1996; Khan et on the ecological requirements of migratory waterbirds al.,1998), differences in the mean maximum and minimum (Boulekhssaim et al., 2006). Information on the time- temperature (Chatterjee et al., 2013; O’Neal et al., 2018), activity budget pinpoints the functional role of wetlands day length (O’Neal et al., 2018), cloud cover (Khan et al., and indicates how changes in the habitats may affect 1998; O’Neal et al., 2018), solar irradiance (Huertas and birds using the ecosystem (Chatterjee et al., 2020). The Diaz, 2001; Visser and Sanz, 2009), precipitation (Khan large variation in the pattern of time-activity exhibited et al., 1998; Draidi et al., 2019), and humidity (Philip et by waterfowl always remains an annoying question. al., 2016; O’Neal et al., 2018). The seasonal pattern of time Many hypotheses have been put forward to account for allocated for feeding by the RCPs during the present study diel feedings, such as the visual selection of food, food was almost consistent with that of previous studies (Paulus abundance, foraging efficiency, niche sharing, competition, 1988; Tamisier et al., 1995; Brochet et al., 2012). A higher metabolic need, and predation risk (Boulekhssaim et foraging time was evident in the present study at the arrival, al., 2006). Incidentally, there is no record of previous i.e. early wintering period, and departure, i.e. late wintering studies on the diurnal time budgets of RCPs. Khan et period, while a decrease was observed in between these 2 al. (1998) recorded that nonbreeding periods. Tamisier et al. (1995) correspond these 3 periods preferred to spend >50% of their time resting. Ali et al. to the wintering strategy of the ducks, namely the restoring, (2016) reported that the proportion of time allocated for pairing, and fattening periods, during which feeding time sleeping ranged between 40% and 75% in white-headed budgets differ. Nilsson (1970) stated that in early and late duck, ferruginous duck, Eurasian teal, common pochard, migratory periods with shorter nights, diurnal feeding and tufted duck. Das et al. (2011) and Draidi et al. (2019) rates might be higher because birds need to spend part also reported similar diurnal activity patterns in fulvous of the day feeding to meet excessive nutrient needs. In whistling duck and ferruginous duck, respectively. In the the current study, comparatively higher day lengths were present study, resting, including sleeping inthe RCPs,was observed to be the proximate reason for higher foraging the dominant activity during the entire wintering period. activities at arrival and departure times. Morrier and Diurnal resting and other comfort activities represented McNeil (1991) also recorded increased feeding rate in 2 a way for rearrangement of energy reserves in wintering plovers, in months with higher day lengths. However, the populations of (Tamisier and Dehorter 1999; ultimate reasons for the higher feeding activity at the onset Draidi et al., 2019). In the present study, swimmingwas the of the wintering period was to make up for the energy loss next prevalent activity. Swimming is an essential activity during arduous in-migration, while the increased feeding associated with foraging in many dabblers. However, time before departure in out-migration could have been for the RCPs, a predominant diver species, a significant attributed to migratory preparedness (Ali et al., 2016). negative correlation between swimming and foraging Laich et al. (2012) and Osterrieder et al. (2014) reported was observed. The time allotted for diurnal foraging was that the dive duration is influenced by prey distribution, always less than 30% of the entire activities. Fasola and depth, and climatic conditions. Intrinsic factors, such as the Biddau (1997) reported that diurnal foraging could be duration of preceding and subsequent inter-dive intervals

435 MUKHERJEE et al. / Turk J Zool and body size, also influence the dive duration and inter- RCPs. However, dabbler-like beak dipping and upending dive interval. Because of the high energy expenditures in were the major foraging techniques under shallow water diving, the ingestion rate should be maximized during conditions for both the males and females. The post hoc each dive to minimize time underwater, with diving spells results attested to this observation. The RCP, a Palearctic simply being ended upon satiation (Richman and Lovvorn, migrant species, is considered as a link between pochards 2004). In sexually dimorphic ducks, the diving durations (Aythyinae) and dabbling ducks (); hence, it is were higher in the case of the larger males; in musk duck, an interesting species from a phylogenetic point of view the larger sex (males) had 10% longer dives and 20% inter- (Johnson and Sorensons, 1999). The present study on the dive intervals than the smaller females due to their greater foraging behavior of RCPs was also interesting to attest to oxygen storage capacity (Osterrieder et al., 2014). Behney their phylogenetic position between divers and dabblers. (2014) observed that the effect of feeding depth on stint duration was much stronger for blue-winged teal (small- 5. Conclusion bodied) than mallards (large-bodied). Male RCPs that were Time-activity, foraging habitats, and feeding techniques 1.4%–8.4% larger than the females (BirdLife International, of waterbirds are important to understand the resource 2019a) showed a higher diving frequency (36.4% higher partitioning and optimal utilization of available resources on average) and duration (35.4% higher on average) in the of the wetlands (Muzaffar, 2004; Chatterjee et al., 2020). present study. Larger lung capacity and larger head:body The present study on the time-activity budget and foraging ratio in male RCPs make them capable of having more techniques of nonbreeding RCPs focused on their ability foraging time in energy expensive diving than the females. to winter in Indian tropical climates, replenish food after Wintering RCPs must prepare for the ensuing breeding migration, and get set before spring migration. Changes in period by balancing the demands of long migratory up- habitat conditions influence their foraging techniques and and-down flights and self-maintenance while functioning thereby, RCPs exploit foraging resources under different habitat conditions by using varied foraging techniques. within phenotypic, energetic, and geographical constraints. Such generalist behavior might be the key to the breeding To meet these challenges, Austin et al. (2019) reported that success and maintenance of a large worldwide population. species must adapt their foraging behaviors in ways that The RCP has an extremely large breeding range (from the ultimately optimize both survival and fitness. British Isles to China) and is evaluated as LC on the IUCN The diet of RCPs consists predominantly of the roots, Red List, even though Defos du Rau (2002) identified seeds, and vegetative parts of aquatic macrophytes, although habitat degradation as one of the threats to this species. they occasionally also consume aquatic invertebrates, Humans affect RCPs in many ways, including habitat amphibians, and small fish (Defos du Rau, 2002; Defos loss, hunting, and pollution (Defos du Rau, 2002; Kear, du Rau et al., 2003). The present study sites harbored 2005). Rapid developmental activities and urbanization varied aquatic macrophytes, associated insects, molluscs, in developing countries, like India, habitat destruction, and fish populations. Johnsgard (1965), in his detailed and anthropogenic disturbances are high (Datta, 2014). work, indicated that RCPs frequently feed by upending; The population limits and degree of isolation for RCPs however, they could dive very well in the usual pochard are not well-known, along with local population sizes in manner of using only the feet. Amat (2000) reported popular wintering areas of India. The ecology of waterbird that RCPs forage either by diving, upending, or dipping communities and particularly, in eastern India, remain their head underwater. In the present study,in addition to poorly studied, while the entire region is an important head dipping, the RCPs were observed to dip their head, wintering ground for migratory waterbirds. This study stretching up to the end of the neck, underwater (thus would offer an important service in managing waterfowl named neck dipping) in shallow water habitats. However, communities and habitats in India. Several monitoring similar head and neck dipping feeding were reported in plans should be implemented so that better information common eider (MacCharles, 1997), ferruginous duck is available for this species and interactions with other (Draidi et al., 2019), common shelduck (Liordos, 2010), waterbirds in the communities. The present study and mallard (Green, 1998b; Liordos, 2010). The present recorded the fundamental information on the functional study interestingly also revealed striking differences in role of wetlands, and how changes in habitats might affect foraging technique usage in deeper water habitats and waterbirds using a particular wetland. shallow water habitats. Furthermore, the techniques also differed between male and female individuals under Acknowledgments such contrasting habitat conditions. Under deep water The authors are thankful to Prof. Sanjoy Chakraborty; conditions, the predominant foraging techniques were the Principal and Dr. Anjan Bis was of the Government diving, followed by beak dipping, for both male and female College of Engineering and Leather Technology, Kolkata;

436 MUKHERJEE et al. / Turk J Zool and Dr. Asitava Chatterjee, DFO, Kangsabati South UGC for awarding the Emeritus Fellowship (F.6-6/2016- Division, Purulia, for their cooperation and necessary 17/EMERITUS-2015-17-GEN-5244/SA-II). infrastructural and laboratory support. The first author is thankful to the University Grants Commission (UGC), Conflicts of interest Government of India for the Junior Research Fellowship The authors declare no potential conflicts of interest with [16-6(DEC.2017)/2018(NET/CSIR] that helped in respect to the research, authorship, and/or publication of completing this work. The last author is thankful to the this paper.

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Annexure I. Macroclimatic factors recorded for the study period.

Mean monthly Nov 2018 Dec 2018 Jan 2019 Feb 2019 Mar 2019 climatic conditions Max air temperature (°C) 30.4 25.6 28.6 28.9 32.5 Min air temperature (°C) 21.5 14.7 14.3 17.6 22.4 Temperature difference (°C) 8.9 10.9 14.3 11.3 10.1 Sunrise (h:min) 5:55 6:14 6:25 6:14 5:51 Sunset (h:min) 16:57 16:55 17:16 17:37 17:50 Day length (h) 11.37 10.73 10.86 11.39 12.33 Solar irradiance (cal. m–2 day–1) 3670.55 3403.82 3609.02 4093.02 4790.82 Rainfall (days/month) 0 3 0 9 11 Rainfall (mm) 0.0 88.5 0.0 74.2 48.4 Cloud cover (%) 10.1 15.7 7.5 22.0 19.4 Humidity (%) 48.4 43.1 38.3 39.1 36.7

Annexure II. Monthly site-wise population size of the RCPs (mean ± SD) (NR: not recorded).

Month Site1 Site2 Site3 Site4 Nov 2018 NR 18.5 ± 1.80 NR NR Dec 2018 185.8 ± 5.31 66.8 ± 7.98 84.0 ± 6.04 14.5 ± 2.89 Jan 2019 431.5 ± 19.93 64.5 ± 4.56 29.8 ± 3.96 80.3 ± 3.30 Feb 2019 124.5 ± 8.38 51.5 ± 4.72 22.0 ± 1.87 101 ± 6.73 Mar 2019 NR 7.0 ± 0.71 2.25 ± 0.43 1.0 ± 0.00

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