Migration gives sleepless nights to the birds: a study on a Palaearctic–Indian migrant, Emberiza bruniceps

Abstract

Migration is a seasonal phenomenon, wherein the birds swap between their breeding and overwintering grounds to avoid harsh climatic conditions and maximally utilize the geographical resources available. The annual cycle of a migratory bird broadly comprises non-breeding and breeding phases. The non-breeding phase corresponds to non-migratory life history state (LHS), whereas the breeding phase can be bifurcated into migratory (spring/autumn migration) and reproductive stages. Since most of the migratory birds are nocturnal migrants, this results either in shift or compromised sleep in these organisms for the sake of their reproduction and survival. Thus, an obvious question arises regarding the prevalence and distribution of sleep in these night migrants. Therefore, the present study focuses on the life history state-dependent as well as daily (with reference to night) differences in sleep behavior with special mention of different sleep postures in a migratory bunting, Emberiza bruniceps. For this purpose, male redheaded buntings were procured from the wild, and after acclimation in laboratory condition, were subjected to short (8L:16D) and long (13L:11D) photoperiodic schedules. Short photoperiod corresponds to non-migratory, whereas long photoperiod leads to pre-migratory and migratory LHSs. The results reveal that sleep behavior varied with different life history states of the bird. Non-migratory and pre-migratory states were dominated by front and back sleep postures, whereas migratory phase was dominated by active wakefulness. Not only life history state, even the night itself showed gradation in occurrence of different sleep behaviors. As the study was conducted in different phases of night, phasic distribution of different sleep behaviors was also observed. Thus, the bird under study, redheaded bunting, clearly demonstrated life history state, as well as daily differences in distribution of different sleep behaviors.