Theses and Dissertations

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    Bird communities and their distribution pattern along the elevation gradient of Teesta Valley, Sikkim
    (SACON, 2008) Acharya, Bhoj Kumar; Vijayan, Lalitha
    Studies on ecology of local communities are important for understanding environmental problems and planning area-based conservation management (Simberloff, 2004). Community composition, species richness and diversity of birds in five different elevation zones of Teesta valley, Sikkim were studied from June 2003 to March 2006 using point count sampling method. A total of 329 species of birds (299 during regular quantitative sampling and 30 during. opportunistic observations) belonging to 44 families was recorded in the Teesta valley during the study period. The study shows that Teesta valley harbors high diversity and abundance of birds. Broadleaved vegetation, situated at mid-elevation region, is the most diverse zone as compared to tropical, coniferous or alpine vegetation. Species accumulation curves based on number of point counts indicated that most of the species were detected in all the zones. Species richness (observed and estimated) was the maximum in zone II, whereas density, abundance and diversity were the maximum in zone iii. The species-abundance pattern of birds followed truncated log-normal distribution for total bird population as well as for all the zones except zone II which did not fit to any models. Bird data showed the presence of both types of species, exclusive (restricted to one elevation zone) and generalists (present in two or more zones), in the Teesta valley. Out of the total species observed (329), 156 (47.4%) were exclusively recorded in one specific elevation zone. Only three species, namely Blue Whistling Thrush, Greenish Warbler and White-capped Water Redstart occurred in all the five zones.
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    Species interactions with in mixed species bird flocks along an Elevational gradient in the Western Himalaya.
    (Wildlife Institute of India, Dehradun, 2021) Gokhale, Pranav; Kumar, R.S.; Mohan, D.
    Mixed-species bird flocks (hereafter, “flocks”) are an interactive community of largely insectivorous birds, which move and forage together to gain enhanced access to resources and protection from predation. In this study, I aimed to investigate a question: do interspecific interactions within mixed-species flocks change along an elevational gradient? To test this, I carried out this study in the Garhwal region of the Western Himalaya in Dehradun District, Uttarakhand from January to April 2021 (spanned across two seasons). The study areas comprised of three field sites along an elevation gradient from western part of the Rajaji Tiger Reserve (300 m ASL) to Mussoorie (2200 m ASL). I sampled flocks and relative abundances of birds on the two pre-existing trails in each of the three field sites. I walked each trail 10 to 13 times. I recorded species identity, group/cluster size of all birds seen inside as well as outside flocks on the trail and within 10 m on either side of the trail. I assessed arthropod prey availability in winter for the flocking species by using branch bagging technique on the same trails. In total, I clipped 150 branches for the three elevations. I calculated species-specific flocking propensity for each elevation from the information on birds seen within and outside flocks. I used network density (potentially realised associations) and weighted degree (associated strength) to quantify the interspecific interactions (associations) within flocks. To control for the influence of species availability on flock network properties, I generated null flocks using an abundance-based null model. I recorded 80 flocking species in 412 flocks, of which, 179 flocks were observed at the High elevation, 156 at the Mid elevation and 77 at the Low elevation. Majority of species in the Western Himalayan flocks were insectivorous gleaner. I found insect prey availability (resource) to decrease with increasing elevation in winter. As expected, flocking propensity, network density and weighted degree increased with elevation in both seasons indicating greater potentially realised associations and high strength of associations between species. Interestingly, the Low elevation flocks disintegrated completely at the onset of summer possibly due to the greater availability of resources, or an upward migration of species for breeding. I did not analyse the Low elevation flocks in summer due to small sample size (n=5). Flocking propensity and network density decreased from winter to summer at Mid and High elevation while, weighted degrees decreased only for the Mid elevation. This is likely that true summer may not have started at the High elevation during the course of my fieldwork. To conclude, with increasing elevation in both seasons, species not just flocked more, but associated with many species and these associations became stronger, potentially due to the scarcity of resources. It is possible that species may not be able to access resources efficiently when foraging on their own at the High elevation, compelling them to participate in flocks to avail complementary benefits from many other species.