How Can Birds Sleep While They're Flying

Sleeping while flying overseas in an airplane
isnt exactly an amazing physical feat. But sleeping while physically flying over
an ocean? Frigate birds do it. Because brains! Hey frequent fliers, Trace with you on DNews
today. Frigate birds have an impressive six-foot
wingspan but their feathers arent waterproof so they cant rest on water, and yet they
spend most of their lives at sea.

The exception is when they breed; they do
that on land. So if they can't land on water, and only come
to land to breed how does this non-waterproof bird stay aloft over the ocean for weeks at
a time? It all comes down to their brains! Most of us probably think of birds as flying
around during the day and resting at night like we do. But frigate birds? Uh-uh. Earlier this year, a team from the Max Planck
Institute for Ornithology in Germany tracked the birds brain activity by fitting them
with small devices able to measure electroencephalographic (or EEG's / brainwaves) changes, including
slow wave sleep and rapid eye movement sleep.

Data was gathered over 10 days while the birds
flew more than 3,000km, and it revealed amazing behaviour. During the day the birds stayed awake, looking
for fish or other birds to harass and steal food from; theyre kinda jerks, but when
you cant land on water that's kinda how you gotta live. Then, at night, their brains did something
super neat. Frigate birds, like humans, have one brain
divided into two hemispheres, but it turns out frigates can shut down and rest only one
hemisphere at a time, engaging it in short-term stages of slow-wave sleep.

In other words, they sleep with one eye open
-- while flying. The birds typically circle upward on air currents
in the direction of their open eye, which is the one connected to the awake hemisphere. The researchers think they do this to watch
where theyre going and so they dont run into other birds. Incredible as this is, frigates are not the
only animal that sleeps with half its brain awake at a time.

Its an unusual sleep pattern called "unihemispheric
slow-wave sleep." Behaviourally, sleep is a period of rest in
a species-specific posture. Physiologically, its a state characterised
by specific eye movements, muscle tonation, and cortical rhythms. In unihemispheric slow-wave sleep, only half
of the cerebral cortex, the gray matter that covers both hemispheres of the brain, displays
the characteristic patterns of sleep, while the other half shows neural activity of a
waking state. During this time the brain cant get into
full REM sleep; it can only fall into shallower, slow-wave oscillation sleep.

Unihemispheric slow-wave sleep is how dolphins
can rest without drowning or being killed. A dolphin will shut down one hemisphere of
its brain, leaving the other half of the brain to monitor breathing function and keeping
that eye open to monitor its environment (the left eye will be closed when the right half
of the brain sleeps, and vice versa). Its also something a lot of birds do, like
mallard ducks -- keeping one eye open to watch for predators while the rest. So this method of getting some shut-eye isnt
exactly unheard of.

But in the study of frigate birds, the researchers
found something even more amazing. Apparently, frigate birds also occasionally
shut down both hemispheres of their brain at once and somehow dont drop out of the
sky like a hot rock. They dont do this for long; only a few
seconds at a time, and all told, between the half-brain sleep and occasional full-brain
sleep, they only get about 42 minutes of shut eye a day when theyre at sea. Humans prefer to rest the whole brain at once,
but amazingly in certain situations, we can also do it a hemisphere at a time too.

In humans, unihemispheric slow-wave sleep
is associated with the first night effect, also known as your inability to get a good
nights sleep in a new location. It's not a full separation between brain hemispheres;
rather, its described as an asymmetry. One hemisphere is more active and vigilant,
monitoring the environment for unfamiliar sounds in the new surroundings. So next time you have a bad night in a new
environment like a hotel or a new apartment, think of how cool it is that your brain is
tapping into the same evolutionary advantage that birds and dolphins use.

Even though youll be too tired to be amazed. Maybe. So have you guys experienced this first
night effect? And speaking of weird ways of sleeping in
the air, what about insects? Do insects sleep? Julian has the answer in this video right
here. Have you guys experienced this first night
effect? Let us know in the comments, make sure subscribe
to you get more DNews and thanks for watching..