19 March is known as World Sleep Day! Now that’s a day we can probably all get behind. Sleeping is pretty neat and a lot of our animal friends seem to feel the same way. When thinking about animals and their sleep habits, the usual suspects come to mind, like cats and bears, but if you think about it, chances are you’ve never seen a bird sleeping, right?
Well, birds’ sleep habits are entirely different from what we traditionally associate with sleeping; to, among other things, best protect them from the ever-looming threat of danger or predators some have developed really incredible adaptations. Today we’re diving into five amazing facts about bird sleep!
Owls are nocturnal! This means they sleep during the day. To do that, adult owls turn their head around and tuck their beak into their back feathers. They do this to keep warm, as the soft and fluffy down feathers trap air and are great for insulation. However, owlets can’t do that yet because their heads are too heavy; they just lie down on their stomach and turn their head to one side, much like baby humans, sleeping for a few hours at a time. No need for cribs, though. Owlets are protected from falling by the hallux, a back toe that grabs onto the branch and keeps them secure in their designated napping spot.
A lot of birds sleep on branches or standing up, which begs the question, how come they don’t fall down? It’s all due to the fascinating anatomy of their feet. These are mostly made up of bones and tendons and, when it comes to sleeping, function like a vice. There are two tendons in their talons, called flexor tendons, that tighten when a bird is perched, effectively closing their grip. When it straightens its legs, the tendons relax and the grip is released! It’s this awesome gripping power that allows tits to hang upside down.
Sleeping with one eye open
Falling asleep can be a pretty dangerous affair, as it leaves you vulnerable to predators and other dangers. A lot of prey animals have to sleep, so to speak, with one eye open and be constantly vigilant, but did you know that some birds actually sleep with one eye open? This is called unihemispheric slow-wave sleep or USWS and is a type of sleep during which one half of the brain remains awake. This allows them to rest and be watchful at the same time; this is done by ducks and other waterbirds, as well as peregrine falcons and Eurasian blackbirds, just to name a few. Not only that, birds can even adjust how awake or asleep they are depending on how much their eye is open!
Sleeping on the wing
You’ve heard of sleepwalking but what about sleep… flying? That’s right, studies have shown that Alpine swifts can actually sleep while flying! They manage to catch short moments of shut-eye when they are high enough that they can glide. While flying, they sometimes make use of the unihemispheric slow-wave sleep mentioned above, but sometimes they also fall asleep with both hemispheres! Alpine swifts actually do most things in the air, staying airborne over six months at a time. Ornithologists have claimed that swifts stay in the air basically all their life, only sometimes landing to breed.
Strength in numbers
It can get pretty cold at night, particularly in winter months. To combat the intense cold, birds sleep in something called torpor – a state during which they will lower their heart and metabolic rate, as well as slow down their breathing. This is done to conserve as much energy as possible. In addition, many birds also engage in something called communal roosting to conserve body heat and provide greater safety in case any predators approach. This is done, among others, by tits, chickadees and bluebirds. The latter especially like to sleep in a heap and, when roosting in tree cavities, tend to fill them up to capacity!