Sleep-swimming in Canada geese (Branta canadensis)

Abstract

Sleep is an imperative behavioral state that is observed in all organisms studied in the literature until now, but its functions are yet to be completely understood. Sleep is known to be homeostatically regulated and sleep deprivation over long periods can lead to severe cognitive and physiological impairments in many species. However, in specific ecological contexts, investing in sleep may be disadvantageous for an individual's fitness. Many bird species prioritize a prolonged waking phase during migration, reproduction, challenging foraging situations or under social restrictions imposed on them. Individuals engaging in such trade-offs gain fitness from such prolonged wakefulness when subjected to these restrictive conditions. Although several possibilities have been suggested, little is known about how birds obtain sleep in such situations. Great frigatebirds (Fregata minor) can sleep while in flight. However, these findings only pertained to passive modes of locomotion and it is unknown whether these birds are also capable of sleeping while in active motion which involve flapping of wings. Interestingly, several waterfowl species have been observed closing their eyelids while swimming, a phenomenon we term as "sleep-swimming." In this thesis project, we demonstrate the presence of “sleep-swimming” in Canada geese (Branta canadensis) by using a combination of accelerometers and video coupled with computer vision and characterise this novel phenomenon. We provide behavioral evidence that sleep could be compatible with locomotion. Our results show geese sleep while swimming in a manner similar to dolphins, but unlike dolphins they show bilateral sleep during motion. We also show that sleep-swimming declines in juvenile geese as they age, a characteristic of normal sleep well established in mammalian systems.