Investigating the plasticity of migration timing and roost behaviours to environmental variability and parental care in a colonial songbird

Abstract

Rapidly changing environments impact avian populations greatly. Indeed, variable weather affects the timing of crucial resource availability and behaviours of breeding birds. Migratory birds are particularly threatened by advancing springs and must adjust their migration timing to remain synchronized with spring phenology. Environmental factors such as weather variability are known to influence bird timing both during breeding and migratory periods but have rarely been investigated for their impact across migration routes. Once birds are at their breeding locations, how environmental factors influence local timing and movements has also been little examined. In this study, in a declining long-distance migrant, the purple martin (Progne subis), I first investigate how extrinsic (environmental), and intrinsic (morphological, migration destination) factors impact migration timing and rate. Second, I investigate the timing of parental roosting during active parental care, and how environmental and nest conditions influence this behaviour. I found that variation in destination and timing are the main influence on spring arrival date and migration rate, while to a lesser extent favourable weather promotes faster migration. The great influence of spring departure on migration rate and arrival suggests selective pressure on migration timing across routes to match with conditions at the breeding grounds. I also found that summer roosting is prominent in purple martins with colder evenings and increased parental investment increasing the odds of parents remaining at their colony at night. Overall, my findings indicate that the influence of environmental factors on movement behaviour may vary by season, with spring migration being mostly driven by intrinsic factors, while summer roosting may be most influenced by local temperature. Future research on the effects of environmental factors on migratory stopover duration and the seasonality of roosting would further our understanding of these timing behaviours and how they may interact with advancing climate change.