3 August 2016
I only dropped off for a second…
Bryson Voirin, Max Planck
Institute for Ornithology.
By Alice Klein
The debate has finally been put
to bed. Wearable brainwave recorders confirm that birds do indeed sleep while
flying, but only for brief periods and usually with one half of their brain.
We know several bird species can
travel vast distances non-stop, prompting speculation that they must nap
mid-flight. Great
frigatebirds, for example, can fly continuously for up to two months. On
the other hand, the
male sandpiper, for one, can largely forgo sleep during the breeding
season, hinting that it may also be possible for
birds to stay awake during prolonged trips.
To settle this question, Niels Rattenborg at
the Max Planck Institute for Ornithology in Seewiesen, Germany, and his
colleagues fitted small brain activity monitors and movement trackers to 14
great frigatebirds.
12-second naps
During long flights, the birds
slept for an average of 41 minutes per day, in short episodes of about 12
seconds each. By contrast, they slept for more than 12 hours per day on land.
Frigatebirds in flight tend to use one hemisphere at a time to sleep, as do ducks
and dolphins, but sometimes they used both.
“Some people thought that all
their sleep would have to be unihemispheric otherwise they would drop from
the sky,” says Rattenborg. “But that’s not the case – they can sleep with both
hemispheres and they just continue soaring.”
Sleep typically took place as the
birds were circling in rising air currents, when they did not need to flap
their wings.
Weather eye
During this time, the brain
hemisphere connected to the eye facing the direction of the turn was more
likely to stay awake.
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