Researchers have found that birds are capable of sleeping during flight. This helps explain how some bird species are able to fly non-stop for weeks or months at a time. The findings are in a paper just published in the journal Nature Communications.
Frigatebirds (Fregata minor) spend most of their lives in flight, above the open ocean. They can fly for weeks without resting, feeding on flying fish and food stolen from other animals. Scientists have speculated that frigatebirds can sleep while in flight but there had never been any hard evidence.
A research team developed a device that could measure electroencephalographic changes in the brain activity of birds. By measuring these changes, the researchers could look for evidence of slow wave sleep and rapid eye movement sleep. They attached the devices to a group of frigatebirds that were nesting in the Galápagos Islands. The birds were tracked during a 10 day flight and the devices were retrieved when the birds were back on land.
The team found that the frigatebirds were occasionally entering slow wave sleep in the evening, when they were done feeding. Interestingly, while they often slept with just one brain hemisphere active, there were times when both hemispheres entered slow wave sleep. These findings show that keeping one hemisphere awake is not required for flight and navigation. The birds also entered rapid eye movement (REM) sleep but for only a few seconds at a time, which is typical for birds.
While the birds had the ability to sleep during flight, they still only slept for about 42 minutes a day. On land, frigatebirds sleep for 12 hours. The researchers aren’t sure why the birds sleep so little, especially since they could sleep at night when not foraging for food. The team hopes to investigate how the birds deal with sleep deprivation. It’s possible that short “powernaps” are enough to get them through their journey. The researchers hope their findings will help us understand the functions of sleep. This type of research may also offer clues as to why sleep deprivation doesn’t affect birds the same way it affects humans and other animals.
Niels C Rattenborg et al. Evidence that birds sleep in mid-flight. Nature Communications (2016).