Temporal changes in species richness of waterfowl (Anseriformes) community in D’Ering Memorial Wildlife Sanctuary, Pradesh, India

: We conducted five yearly field surveys to assess long-term changes in the species richness, abundance, and composition of waterfowl populations (Anseriformes) in the D’Ering Memorial Wildlife Sanctuary, a significant staging area on migratory flyways with one of the largest concentrations of waterfowl in Arunachal Pradesh, especially during winter. A total of 8,040 birds belonging to 17 species of Anatidae were recorded, including two threatened species. The most abundant species were Tadorna ferruginea , Anas poecilirhnycha , and Bucephala clangula , with relative abundances of 29%, 10%, and 9.4%, respectively. Species richness was highest in winter (H’= 2.40; January H’= 2.43) and lowest in the monsoon (H’= 1.48; August, H’= 1.12). Seasonal difference in species richness was noticed for winter visitors, but not for year-round residents. We observed a major declining trend for seven species. Findings from this study can be used for further ecological assessment of the waterfowl community of the sanctuary. Ngolu (Anseriformes)


INTRODUCTION
Habitat is a fundamental unifying entity and concept in wildlife ecology and conservation (Block & Brennan 1993), its use and selection vary seasonally, especially for migratory species (Kaminski & Elmberg 2014). Habitat configuration and composition of the landscape affect the occurrence of species and richness (Guadagnin & Maltchik 2007;Mora et al. 2011;Xu et al. 2014;Zhang et al. 2018), and the seasonal distributions of waterbirds are influenced by various conditions like habitat types, climatic conditions, resource stability, and immediate human impact. Availability of water bodies, wetland size, and wetland connectivity positively affect waterfowl species occurrence and richness (Guadagnin & Maltchik 2007;Zhang et al. 2018). There is about 75,819 km 2 of wetlands in India, which make up 5% of the world's wetland area (AWB & WWF-India 1993), covering 4.1 million hectares and corresponding to 18.4% of the country's land area (MoEF 2003). A total of 2,175 wetlands, covering a total area of 1.5 million hectares, are natural, and 65,254 are manmade, with a total area of 2.6 million hectares (Chatrath 1998). At present, 46 sites in India have been designated as wetlands of international importance, especially as waterfowl habitats (Ramsar Sites) covering an area of 1,083,322 hectares (Ramsar Sites Information Service, 2021). D'Ering Memorial Wildlife Sanctuary (DEMWS) is the only wildlife sanctuary with subtropical forest, grassland, riverine, and inland water body habitats in Arunachal Pradesh, harbouring a variety of waterfowl species and other birds. Birdlife International has declared DEMWS an Important Bird Area (IBA). Covering an area of 190 km 2 , the entire area is a riverine plain criss-crossed by the rivers Siang and Sibia, forming several riverine islands. The sanctuary's dominant grasses are Arundo donax, Erianthus ravannae, Imperata cylinderica, Phragmites karka, Saccharum spontaneum, S. arundinaceum, & Neyraudia rennaudiana and dominant tree species are Albizzia procera, Amoora wallichi, Bombax ceiba, Dalbergia sisoo, Daubanga grandiflora, Dillenia indica, Lagerstroemia speciosa, & Terminalia myriocarpa. The altitudinal gradient of the sanctuary ranges 135-140 m, which gradually decreases from north to south. Within a 10-km radius of the sanctuary are 22 villages with a population of 40,065 (2011 census). The whole sanctuary is surrounded by river water on all sides, making it suitable for various migratory waterfowl.
The term 'waterfowl' has been applied to the members of the family Anatidae, popularly known as ducks, geese, swans, and smaller teals (Delacour 1974). The Ramsar Convention, on the other hand, defines waterfowl as birds 'ecologically dependent on wetlands', and in the second edition of Wetlands International and Waterfowl Population Estimates, waterfowl was defined more precisely as all species of the 33 families (WI 2002). Among these 33 families, eight families are found in DEMWS (Mize et al. 2014), viz., Phalacrocoracidae, Anhingidae, Ardeidae, Ciconiidae, Anatidae, Charadriidae, Scolopacidae, and Laridae.
As per our preliminary field investigations and interactions with hunters of the villagers residing near the sanctuary area, we have found that waterfowl belonging to the family Anatidae (ducks, geese, and swans, hereinafter 'waterfowl') are frequently hunted for meat and traded by them. Considering this vital information and the significance of DEMWS, an effort has been made to investigate the long-term temporal changes, species richness, and species abundance of the waterfowl (Anseriformes) community in DEMWS. This information will be useful for better understanding the underlying mechanisms of how seasonal variation affects different migratory species of waterfowl in the sanctuary, so that targeted conservation strategies can be developed. The study will also add to the existing information on the previous checklist of birds of DEMWS and stimulate interest in waterfowl watching, which will help the wildlife division and researchers.

Study Area
The study was carried out in the D'Ering Memorial Wildlife Sanctuary (DEMWS) in the East Siang District of the state of Arunachal Pradesh, northeastern India. The sanctuary area is divided into three managerial ranges, namely, the Anchalghat Range, the Sibiamukh Range, and the Borguli Range ( Figure 1). It is located at latitudes ranging from 27.850-28.083 N and longitudes from 95.366-95.483 E. In terms of topography, 80% of the sanctuary is grassland, with the remaining being riverine forest patches with mixed bamboo and secondary forests. The region has climatic conditions that are subtropical with average temperature variations of 5 °C during winter to 45 °C during summer and comprises four seasons, taking mean climatic conditions into account, viz., pre-monsoon (March-May), monsoon (June-August), post-monsoon (September-November), and winter (December-February). The lowest rainfall occurs in January with an average of 41.80 mm, and the highest rainfall occurs in July with an average of 1,433.20 mm.

Field Surveys
Five-year field surveys were carried out from March 2015 to February 2020, dividing the year into four seasons. For the waterfowl survey, a modified point count method-vantage points counts-was used (Bhupathy et al. 1998). A total of 15 vantage points were designated, covering the whole of the Anchalghat Range and Sibiamukh Range of DEMWS, based on the best visibility of the site from where the fixed-area was scanned for waterfowl flocks (Figure 1). Due to logistical constraints, the Borguli Range of the Sanctuary was excluded for the study. Each vantage point was visited at least once every month on foot on days with suitable weather, avoiding rainy days because rain interferes with visibility (Ralph et al. 1993). Twenty minutes were spent at each vantage point recording waterfowl in the water or on the shoreline and its vicinity using binoculars (8 × 56 and Olympus 10 × 50); almost 65% of our observations were photo-documented with a DSLR camera (NIKON, D5200 with 70-300 mm lens). Waterfowl species were identified following Grimmett et al. (2011) and Ali & Ripley (1995); and we followed the classification used in the checklist of the birds in the Oriental Region, Oriental Bird Club (Inskipp et al. 2001) for species' systematic position (order, family), common name, and scientific name. A Garmin GPS device with a mobile app was used to record the locations for conducting the waterfowl survey at that particular sampling vantage point. Waterfowl were found active the most after sunrise to midmorning and before sunset; therefore, the timing was adjusted depending on the day length of the seasons, viz., late sunrise in winter and post-monsoon observation was done (0600-1100 h) and (1400-1630 h) and early sunrise in pre-monsoon and monsoon observation was done (0500-1000 h) and (1430-1730 h). The count period covered all the seasons, but the most extensive data was collected in the years 2018-2020, and less frequent counts occurred in 2015-2017, when counts were not able to cover all three months of the monsoon seasons due to heavy rainfall and heavy floods along the Siang River, as already mentioned in the study area.

Data Analysis
The relative abundance of a species is its percentage among all species utilising the same habitat (Simon & Okoth 2016;Walag & Canencia 2016;James et al. 2017). By assessing the relative abundance of species, one can identify the most common or rare species in a given area. The relative abundance (%) of waterfowl species was determined using the following formula: Where, ni= total number of waterfowl of each species and N= total numbers of waterfowl of all species detected in DEMWS following (Bibby et al. 2000;Hubbell 2001;McGill et al. 2007).
Strictly regarding study area, based on presence or absence of species throughout the study periods, we have distinguished four categories of relative seasonal occurrence and residential status of waterfowl as: (a) year-round residents-waterfowl recorded throughout the year; (b) winter visitors-waterfowl recorded in abundance during winter seasons; (c) monsoon migrants-species that occur only during the monsoon; and (d) passage migrants-waterfowl that stay for a short time in the sanctuary during the study period. The abundance status of the recorded waterfowl species was established, viz., common (C), fairly common (FC), uncommon (UC), and rare (RA), based on frequency of sighting following (Kumar & Gupta 2009). The conservation status and global trend were assessed according to IUCN (2021). The diversity indices were determined as follows: Simpson's diversity index (1-D) (Simpson 1949), Shannon-Wienner index for alpha diversity (Shannon & Weinner 1949), Margalef index for species richness (Margalef 1958), and Pielou's evenness index for species evenness (Pielou 1966 Where S= number of observed species H'= Shannon-Wiener index All survey data were compiled using Microsoft Excel Version 2010. The yearly observations and diversity index data were pooled together within four seasons to test the seasonal pattern of the waterfowl assemblage in DEMWS. The data was further subjected to non-parametric Kruskal-Wallis tests with subsequent post-hoc Tukey's HSD (Honestly Significant Difference) tests, performed separately to determine the seasonal difference between species richness across all the seasons in DEMWS as well as between year-round residents, winter visitors, monsoon migrants, and passage migrants. Statistical tests were computed using PAleontological STatistics Version 4.03. All statistical tests were set at a significance level of p <0.05.

RESULTS
During the five-year study in DEMWS, we have recorded 8,040 birds of waterfowl belonging to 17 species of the family Anatidae of the Order Anseriformes at a rate of 1,608 birds per year (Table 1, Image 1-12). The most abundant species are Ruddy Shelduck Tadorna ferruginea, followed by Indian Spot-billed Duck Anas poecilorhyncha and Common Goldeneye Bucephala clangula, with relative abundances of 28.96%, 10.24%, and 9.38%, respectively (Table 1). The relative seasonal and residential status of different waterfowl species indices. The present study shows an increasing trend in the yearly total population of waterfowl (Figure 6), and a major declining trend of population of seven species (Figures 7 & 8) The number of winter visitors significantly increased in October-November (post-monsoon season), reached its peak in January (winter) and then sharply declined in the pre-monsoon ( Figure 5). The results of the Tukey's HSD post-hoc tests using the Lund-Lund (1983) procedure also revealed that the species richness of year-round residents varies insignificantly (Table 2), whereas the species richness of winter visitors varies significantly (p <0.05) ( Table 3). The Tukey's HSD Multiple Comparison test among all seasons also shows significant at p <0.05; winter vs pre-monsoon (p= 0.000591), winter vs monsoon (p= 0.000225), and winter vs post-monsoon (p= 0.000465) ( Table 4).

DISCUSSION AND CONCLUSION
The results showed the presence of 17 species of waterfowl (Anseriformes) in DEMWS. This includes the first-time reports of three species from DEMWS: Baer's Pochard Aythya baeri, Fulvous Whistling Duck Dendrocygna bicolor, and Red-breasted Merganser Mergus serrator. These species were not reported from the sanctuary by early observations (e.g., Rahmani et al. 1991;Singh 1995;Barman 1996;Choudhury 1996Choudhury , 2002Mize et al. 2014;Hussain et al. 2019). The other 13 species were already recorded and cited earlier (Barman 1996;Borang 2013;Mize et al. 2014). The present study shows high temporal changes in the waterfowl community, as shown in the results. In contrast to the increasing trend of the total population of waterfowl in the study area ( Figure 6), there is a major declining trend among the seven species of waterfowl ( Figure 6). Year-wise records of declining waterfowl populations are provided in Figure 7.
Globally, 28% of all assessed species are threatened with extinction (IUCN 2021), confirming the importance of monitoring species' abundance. Baer's Pochard Aythya baeri, Common Pochard Aythya ferina and Ferruginous Pochard Aythya nyroca are the Critically Endangered, Vulnerable and Near Threatened waterfowl species, respectively, recorded in DEMWS (IUCN 2021). Baer's Pochard was classified as vulnerable in 1994 but, following an assessment that probably fewer than 1,000 individuals remained, it was listed as Endangered in 2008 (Wang et al. 2012). It was upgraded to Critically Endangered (BirdLife International 2021). The largest flock of 30 birds was observed in January 2016. The last observation was flocks of six birds diving almost 2 km away from the observer near the Sibiamukh range in February 2020. Baer's Pochard is extremely difficult to find anywhere in its range (Richard et al. 2013) hence, this observation needs attention from the scientific world as this globally threatened bird has a serious contraction in wintering distribution and is heading for extinction in the wild (Chowdhury et al. 2012;Wang et al. 2012;Richard et al. 2013). The Common Pochard Aythya ferina a globally threatened waterfowl breeds largely in freshwater to the south of the tundra region across the Palearctic, from Iceland to the steppe lakes of Mongolia and the Daurian region (Kear 2005). However, due to rapid population decline across the majority of the range, it has therefore been uplisted to Vulnerable (BirdLife International 2021). During the study periods, a total of 400 adult individuals   Throughout the five years of waterfowl surveys in the sanctuary, we did not encounter the White-winged Duck Asarcornis scutulata, an endangered species recorded earlier from the sanctuary (Barman 1996;Choudhury 1996Choudhury , 2002. There have been no sighting records of this waterfowl in the sanctuary for the last eight years, the last being November 2012 (Mize et al. 2014). However, this bird has been reported from various locales including Nameri National Park, Assam (Saikia & Saikia 2011;Das & Deori 2012); Pakke Tiger Reserve, Arunachal Pradesh (Selvan et al. 2013); in Hollongapar Gibbon Sanctuary, Assam (Sharma et al. 2015); at Hkakabo Razi Landscape, Kachin State, Myanmar (Lin et al. 2018). Although we made an extra effort to locate this waterfowl in suitable areas by following (Saikia & Saikia 2011), it was in vain. Field staff reports and the extent of suitable habitat in the study area suggest that this species is perhaps not seen in DEMWS, as all the suitable habitat for this waterfowl has been destroyed by the frequent flooding of Siang Rivers and changing watercourses.
Long-term monitoring of population numbers, population structure, and demographic rates improves our understanding of the biological reasons for population trends (Nichols 1991;Thomas & Martin 1996). DEMWS seems an important staging place on migratory flyways and has one of the highest populations of waterfowl in Arunachal Pradesh, especially during the winter. Furthermore, some globally threatened waterfowl like Baer's Pochard Aythya baeri, Common Pochard Aythya ferina, and Ferruginous Pochard Aythya nyroca are also supported in this sanctuary. Due to logistic issues as well as monsoon floods on the Siang River, it was difficult to cover whole areas of DEMWS and all months of the year. Nonetheless, in this study, we have attempted to cover all the months of various seasons in the most suitable ranges of the sanctuary. Our findings on the temporal changes of waterfowl in this sanctuary can be used for further ecological assessment of the waterfowl community. Nevertheless, detailed studies should be undertaken, focusing especially on the habitat use, nesting, breeding, and foraging ecology of these waterfowl, to understand their critical role in performing various ecosystem services and the underlying causes of the variation in trends.

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