Avian Versus Mammalian Sleep: the Fruits of Comparing Apples and Oranges

Abstract

Insight into the functions of sleep in humans can be gained through studying sleep in animals. In contrast to model-based approaches which emphasize similarities between sleep in humans and animals amenable to experimental manipulation, comparative-based approaches give equal emphasis to the similarities and differences in sleep across the animal kingdom, and thereby aim to reveal overarching principles not readily apparent using other approaches. Avian sleep serves as a prime example. Birds independently evolved rapid eye movement (REM) and non-REM sleep, states that are in many, but, importantly, not all respects comparable to those in mammals. When compared to the sleep traits specific to one group, those shared by mammals and birds are more likely to be involved in fundamental functions. In this review, we summarize recent advances in our understanding of avian sleep, and the implications that such comparative work has for understanding sleep in mammals, including ourselves.