Studying barn owls in the wild, the researchers discovered that this change in sleep is strongly correlated with the expression of a gene involved in producing dark, melanic feather spots, a trait known to co-vary with behavioural and physiological traits in adult owls. (Agencies)
These findings raise the intriguing possibility that sleep-related developmental processes in the brain contribute to the link between melanism and other traits observed in adult barn owls and other animals.
Sleep in mammals and birds consists of two phases, REM sleep (Rapid Eye Movement Sleep) and non-REM sleep. We experience our most vivid dreams during REM sleep, a paradoxical state characterized by awake-like brain activity.
One of the most salient features of REM sleep is its preponderance early in life. Many mammals spend far more time in REM sleep during early life than when they are adults.
Although birds are the only non-mammalian group known to clearly engage in REM sleep, it has been unclear whether sleep develops in the same manner in baby birds.
Researchers in the new study used an electroencephalogram (EEG) and movement data logger in conjunction with minimally invasive EEG sensors designed for use in humans, to record sleep in 66 owlets of varying age.
Despite lacking significant eye movements (a trait common to owls), the owlets spent large amounts of time in REM sleep.
"During this sleep phase, the owlets' EEG showed awake-like activity, their eyes remained closed, and their heads nodded slowly," said Madeleine Scriba from the University of Lausanne.
The researchers discovered that just as in baby humans, the time spent in REM sleep declined as the owlets aged.
In addition, the team examined the relationship between sleep and the expression of a gene in the feather follicles involved in producing dark, melanic feather spots.
"As in several other avian and mammalian species, we have found that melanic spotting in owls covaries with a variety of behavioural and physiological traits, many of which also have links to sleep, such as immune system function and energy regulation," said Alexander Roulin from the University of Lausanne.
The team found that owlets expressing higher levels of the gene involved in melanism had less REM sleep than expected for their age, suggesting that their brains were developing faster than in owlets expressing lower levels of this gene.
In line with this interpretation, the enzyme encoded by this gene also plays a role in producing hormones (thyroid and insulin) involved in brain development.
Studying barn owls in the wild, the researchers discovered that this change in sleep is strongly correlated with the expression of a gene involved in producing dark, melanic feather spots, a trait known to co-vary with behavioural and physiological traits in adult owls.