Elevational species replacement, the replacement of closely related species along an elevational gradient, is one of the most widely documented but least understood ecological patterns. Our current understanding is mostly based on attempting to explain patterns across communities. The objective of the research that Sahas Barve (M.Sc. WII; Ph.D. student Cornell University) and I are undertaking is to identify the mechanisms that create this pattern.  We combine year-round studies of populations with experiments to test the importance of interspecific competition, predation and blood physiology in limiting species distributions of a group of closely related resident cavity-nesting species belonging to the family of the titmice (Paridae).The campus of the Wildlife Institute of India is one of the study sites where we can study a low-elevation great tit population in the absence of other tit species. We placed 50 nest boxes on campus and use these to study great tit reproduction. In April 2014 we colour banded all males and most females and were able to determine the use of the campus and its nest boxes.  Most of the pairs identified, use a nest box for breeding.

Through checking the nest boxes regularly, we acquire exact dates for each step in the reproductive cycle like nest building, initiation of egg-laying, incubation period, fledging period for each pair. This not only adds data to our research but also proves important in understanding other significant aspects of great tit breeding phenology.Unlike temperate regions, in tropical and sub-tropical habitats, the initiation of breeding in birds is not strongly governed by the temperature but rather by the availability of food. For most passerine birds this means small insects to feed young hatchlings. Although this is speculation, but based on our observations, we feel that great tits in Dehradun synchronize breeding with the flowering of Sal (Shorea robusta) trees. Sal trees mast every year at the beginning of summer (in turn governed by the length of winter), being the dominant tree species in the forest, their flowers and seeds probably induce an arthropod explosion. Birds like great tits probably track this phenomenon closely and time their breeding in tandem with the Sal flowering and leafing cycles. In the coming years, long-term nest box studies on WII campus will shed light on how resilient breeding phenology of common birds like great tits areto the annual fluctuations in climate leading to changes in Sal flowering phenology.

The results obtained in Dehradun can be used to compare morphology, physiology and reproduction with those of great tit at high elevation, and with those of other species (especially the green-backed tit) in plots at different elevations in the western Himalayas.

Legend to figures:
Top: André Dhondt (holding great tit) and Sahas Barve (holding green-backed tit), two closely related species that replace each other along the Himalayas.

Middle: complete clutch of a great tit in a nestbox on the campus of the WII

Bottom: a great tit pair exploring nestbox # 49. The pair used the box for breeding.

Map of nest-box locations on the WII campus.