Elevational range and timing of breeding in the birds of Ladakh: the effects of body mass, status and diet

Abstract

We studied the effects of body mass, status (resident or migratory) and diet on the breeding elevation range and timing of reproduction of the birds in the Trans-Himalayan region of Ladakh, northwestern India. Most of breeding birds of Ladakh are Palearctic or breed at high elevations in the mountains. There is a small proportion of Oriental species, and no bird is endemic to this region. We found that heavier birds tended to start their egg-laying earlier than lighter ones. Since body mass is related to the length of incubation and nesting periods, it would appear that one result of this phenomenon is that the time of peak demand for food for most birds coincides with peak food abundance in summer. Status affected the elevation of the breeding range, with resident birds tending to breed at higher elevations than summer visitors. Residents and summer breeders also differed significantly in their diet composition, with the former feeding mainly on plants and seeds, and the latter feeding on molluscs, insects and worms.