Correlates of avifaunal diversity along the elevational gradient of Mardi Himal in Annapurna Conservation Area, Central Nepal

Background Patterns of biological diversity and richness can vary along the elevational gradients among mountain systems making it difficult to conclude the general pattern. The drivers of such pattern are also poorly known in the southern flank of the Himalaya due to limited studies. Therefore, we assessed the species richness, seasonal patterns and drivers of avian diversity along an elevational gradient on Mardi Himal trekking trail, a newly open tourist route in Annapurna Conservation Area of the central Himalaya.

Methods Two surveys (winter and summer seasons of 2019) were conducted from the bank of Seti-Gandaki River confluence (1030 m above sea level, asl) up to the Low Camp (3050 m asl) of the Mardi Himal. The point count method was employed in every 100 m rise in the elevation. Diversity indices were calculated and bird abundance data on species, sites, seasons and environmental variables were analyzed. Generalized linear model, polynomial regression and ordinary least square regression were performed to examine the importance of environmental factors in shaping the avian richness pattern.

Results A total of 673 individuals of birds belonging to 112 species, of which 72 in winter and 80 in summer, were recorded. We observed a hump-shaped pattern of the overall species richness along the elevational gradient. The richness pattern remained consistent even when explored by season, for winter and summer separately. Diversity indices were found higher during the summer. Elevation and mean monthly temperature in both seasons showed non-linear relation with avian species richness. Precipitation exhibited positive association in summer whereas the same in winter was negatively correlated with avian species richness. Distance to the nearest water source and the nearest human settlement were negatively correlated with the richness of birds. Small-ranged and insectivorous birds were under the strong influence of gradients on climatic variables like temperature and precipitation.

Conclusions We conclude that the combined effects of multiple factors such as area, gradients of climate (i.e. temperature and precipitation), resource availability and disturbance play an important role in bird diversity and richness pattern along an elevational gradient of a montane environment in Mardi Himal.