BackgroundUnderstanding diversity patterns and the mechanisms underlying those patterns along elevational gradients is critically important for conservation efforts in montane ecosystems, especially those that are biodiversity hotspots. Despite recent advances, consensus on the underlying causes, or even the relative influence of a suite of factors on elevational diversity patterns has remained elusive.Methods and Principal FindingsWe examined patterns of species richness, density and range size distribution of birds, and the suite of biotic and abiotic factors (primary productivity, habitat variables, climatic factors and geometric constraints) that governs diversity along a 4500-m elevational gradient in the Eastern Himalayan region, a biodiversity hotspot within the world's tallest mountains. We used point count methods for sampling birds and quadrats for estimating vegetation at 22 sites along the elevational gradient. We found that species richness increased to approximately 2000 m, then declined. We found no evidence that geometric constraints influenced this pattern, whereas actual evapotranspiration (a surrogate for primary productivity) and various habitat variables (plant species richness, shrub density and basal area of trees) accounted for most of the variation in bird species richness. We also observed that ranges of most bird species were narrow along the elevation gradient. We find little evidence to support Rapoport's rule for the birds of Sikkim region of the Himalaya.Conclusions and SignificanceThis study in the Eastern Himalaya indicates that species richness of birds is highest at intermediate elevations along one of the most extensive elevational gradients ever examined. Additionally, primary productivity and factors associated with habitat accounted for most of the variation in avian species richness. The diversity peak at intermediate elevations and the narrow elevational ranges of most species suggest important conservation implications: not only should mid-elevation areas be conserved, but the entire gradient requires equal conservation attention.

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The species richness pattern along spatial scales (latitudinal or elevational) forms useful tools in understanding diversity gradients and their underlying mechanisms. Understanding elevational diversity patterns of biodiversity have strong conservation implications. Himalayas are unique systems in exploring such gradients as they harbor tallest mountains in the world. Here, we explored the elevational pattern, its underlying causes, turn over rate and range size distribution of butterflies in Sikkim, Eastern Himalaya, India. We followed fixed width point count method for sampling butterflies covering 1014 points spread over 23 transects along the elevation gradient (300-4700 m) in Sikkim. Data on environmental factors and habitat parameters were obtained from our published literatures of the same study system. During this study we observed a total of 2749 butterflies representing 161 species and six families. Species richness pattern of butterflies followed declining trend along the elevation gradient with a hump at around 1000 m. Various environmental factors and habitat variables correlated strongly with the species richness and abundance of butterflies. Among the set of factors, mean annual temperature and actual evapotranspiration remained the most important determinants reflecting the importance of energy and productivity for butterfly distribution in the Eastern Himalayan elevation gradient. Butterflies showed high turnover along the gradient. Elevational range profile of butterflies showed that around 38.5 % species restricted below 2000 m elevation. We observed that low elevation areas are important for conservation of butterflies in the Eastern Himalaya although entire elevation gradient is crucial for small range-sized species.

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Foraging ecology of the globally endangered Nilgiri Wood Pigeon (Columba elphinstonii) was investigated in the Western Ghats, India, using faecal sampling and direct observations. The birds fed on fruits of 39 plant species, on seeds of 11 species, flowers and leaf buds of four species and a few ground invertebrates. Direct observations across seasons showed nine plant species were selected more often (47% of observations), with fruits of the members of the family Lauraceae the most preferred. Gleaning accounted for 76% of feeding methods throughout the year. Feeding was mainly from twigs at the edges on the upper and middle canopy (> 6 m). Frequency of feeding on fruits correlated significantly with fruit abundance, which depended on rainfall. The present study indicates that the pigeon requires a wide variety of diets from different forest environments. Conservation of this species depends on preserving all habitat types required to meet their resource needs throughout the year.