For the last 15 or so years, scientists around the world have discovered that birds, which are more closely related to reptiles than mammals, exhibit sleeping brain activity similar to that of people (and mice and manatees), engaging in both REM and non-REM sleep. “There must be something about being a bird and being a mammal that causes their brains to need the same kinds of sleep,” says John Lesku, a lecturer at La Trobe University in Melbourne, Australia.

But there are also differences in the brain activity of sleeping mammals and birds, says Niels Rattenborg, who leads the avian sleep group at the Max Planck Institute for Ornithology in Seewiesen, Germany. Unlike mammalian REM sleep, which usually occurs in relatively few episodes that can span several minutes to an hour or more, avian REM sleep typically occurs in hundreds of brief spurts, each lasting just seconds (Curr Biol, 24:R12-R14, 2014).

While the functions of sleep in birds, as in mammals, have been hotly debated, Lesku and Rattenborg say the evidence implicating memory formation and storage is strong. “Several studies suggest that the brain rhythms we see during sleep are playing a role in processing information acquired during the previous day,” says Rattenborg. For example, neurons involved in song production are active in the brains of sleeping juvenile songbirds that learn tunes from adult tutors while awake during the day (J Neurophysiol, 96:794-812, 2006). And researchers have speculated that slow-wave sleep promotes a reduction in synapse strength, weakening less-important memories from the recent past, “so that, at the end of sleep, you’re ready for a new day of learning,” says Lesku.

Fascinating. I believe sleep is essential for memory formation and storage.