AUGUST 19, 2019
by Cell Press
When driving across country, people can only make it so far before stopping off to rest. Likewise, most migratory songbirds must make stops during their long-distance journeys to sleep along the way. Now, researchers have evidence that songbirds tuck themselves in differently depending on just how worn out they really are.
As reported in the journal Current Biology on August 19, birds that are low on fat reserves will tuck their heads under their feathers for a deep snooze. They do so despite the fact that this more restful sleeping position slows their reaction to the sound of potential trouble. By comparison, birds in better shape stop and sleep with their head facing forward, untucked, and more alert.
"We discovered that migratory birds trade off safety for lower energy expenditure," said Leonida Fusani of the University of Vienna and University of Veterinary Medicine, Austria. "If they sleep with their head tucked in the scapular feathers, they enter a sort of deeper sleep that is associated with lower energy consumption but exposes them to a higher predation risk. Consequently, birds in good condition sacrifice some energy to sleep more safely with the head untucked, whereas birds in poor condition sacrifice vigilance to save energy while sleeping unsafely tucked in."
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