First, a little background on sleep: Sleep in mammals and birds has two phases, REM and non-REM. REM, which stands for “rapid eye movement,” gets its name from the quick and random movements the eyes make during this phase. REM sleep is the time of vivid dreams. Non-REM sleep comes first, though, and the body cycles through non-REM and REM sleep throughout the night. Adult humans spend about 20 to 25 percent of their sleep in REM. Newborn babies, though, spend half their night in the REM phase.
And so do baby owls, finds a new study published in Frontiers in Zoology. A team of scientists from Switzerland and Germany outfitted 66 barn owl nestlings with a small data logger that measured brain activity and head movements. The researchers recorded the owlets’ sleep for up to five days, then removed the equipment, letting the owls grow up normally.
In the owls, REM sleep lacks the eye movements that characterize this phase in humans. But the brain recordings revealed that the owlets spent about half their sleeping time in the REM phase. The brain activity was similar to when the nestlings were awake, a key sign of REM, and they nodded their heads slowly as they slept.
Image credit: Fabrizio Sergio