You call a person who stays awake late a "night owl," but a new study suggests that humans have something in common with the birds even while asleep.

A study by researchers at the Max Planck Institute for Ornithology and the University of Lausanne in Switzerland found that baby owls sleep like baby humans, spending a larger portion of their resting hours in REM-sleep than their grown-up counterparts.

The paradoxical high brain activity during periods of deep REM, or Rapid Eye Movement, sleep has been extensively studied but the essence of its purpose still a mystery to researchers.

Birds -- like humans and other mammals -- have two stages of sleep: REM and non-REM. A variety of mammals, including humans, spend far more time in REM sleep when they are infants then when they are fully grown. Human newborns, for instance, spend about half of their sleeping life in REM sleep, whereas adult humans usually spend no more than a quarter of their sleep time in REM.

But until now it has been unclear whether sleep develops the same in birds, which are the only non-mammalian group of animals that also clearly engage in REM sleep.

Researchers attached electroencephalogram (EEG) sensors to 66 owlets of various ages for five days and recorded biometric data and confirmed that owlets spend large amounts of time in REM sleep.

Madeleine Scriba from the University of Lausanne said, "During this sleep phase, the owlets' EEG showed awake-like activity, their eyes remained closed, and their heads nodded slowly"

Scriba and her colleagues also confirmed that owls, like humans, spend less time in REM sleep as they age.

In their study, the researchers also tried to account for a relationship between sleep and a gene in the owls that produces melanic, or dark, spots on their feathers. Owls with the most melanic spotting were observed to also have the least REM sleep during the study, something the researchers suggest means the melanic owls' brains were developing faster than in owlets expressing lower levels of this gene.

"As in several other avian and mammalian species, we have found that melanic spotting in owls co-varies with a variety of behavioral and physiological traits, many of which also have links to sleep, such as immune system function and energy regulation", notes Alexander Roulin from the University of Lausanne.

In conclusion, the researchers state that "given its role in brain development, variation in nestling REM sleep may lead to variation in adult brain organization, and thereby contribute to the behavioral and physiological differences observed between adults expressing different degrees of melanism."

Niels Rattenborg from the Max Planck Institute for Ornithology hopes that "this naturally occurring variation in REM sleep during a period of brain development can be used to reveal exactly what REM sleep does for the developing brain in baby owls, as well as humans."

The research is published in the journal Frontiers in Zoology.