Altitudinal migration is the seasonal movement of organisms between higher-elevation breeding grounds and lower-elevation wintering grounds. Despite altitudinal migration being a common phenomenon (for instance, 70% of birds in the Himalayas migrate altitudinally), the abiotic and biotic drivers of altitudinal migration remain poorly understood. This is important because 85% of global terrestrial biodiversity is concentrated in mountains, and these species are vulnerable to the impacts of climate change. I propose to describe avian altitudinal migration in the Himalayas and determine the role of diet and thermal niche tracking in driving these seasonal movements.

The study site for my thesis is Eaglenest Wildlife Sanctuary, Arunachal Pradesh, which is part of the Eastern Himalayan Biodiversity Hotspot and is home to >350 breeding bird species. I first use a large open-source citizen science dataset to describe various altitudinal migration strategies across the Himalayas. I then go on to assess the various eco-morphological and functional traits as predictors of avian altitudinal migration. I then plan to determine whether migratory birds are tracking their thermal niche or dietary resource availability. For various species, I will assess and compare the degree of overlap in temperature and arthropod availability in their breeding and wintering grounds. Finally, I plan to investigate if diet can explain why certain birds migrate while others prefer to stay back in the harsh winter. I will determine bird diets using DNA metabarcoding on bird faecal samples. Given the various limitations of the DNA metabarcoding technique, I plan to use a complementary method to investigate diet – I will use stable isotope ratios of carbon and nitrogen in whole blood to compare the seasonal trophic niches of resident and altitudinal migrants in the eastern Himalayas. Results from this work will thus help improve our understanding of how and why birds migrate altitudinally, and will have implications for the conservation of montane biodiversity in the face of climate change.