Sleeping Birds

I previously wrote a post explaining why birds don’t fall out of trees while they are sleeping. Not falling out of a tree has to do with the arrangement of muscles and tendons on the lower legs, but this explanation mainly applies to those birds in the Order Passeriformes, the Perching Birds. But not to all of them. Apparently the Eurasian Starling doesn’t use this same mechanism; it uses its innate balance to stay perched upright, even when sleeping.

I previously wrote a post explaining why birds don’t fall out of trees while they are sleeping. Not falling out of a tree has to do with the arrangement of muscles and tendons on the lower legs, but this explanation mainly applies to those birds in the Order Passeriformes, the Perching Birds. But not to all of them. Apparently the Eurasian Starling doesn’t use this same mechanism; it uses its innate balance to stay perched upright, even when sleeping.

And although shorebirds and flamingoes don’t perch on branches, they often sleep while standing on one leg. Turns out that shorebirds, flamingoes, and waterfowl have a mechanism of tendons and ligaments that lock in place to keep the leg rigid, thus avoiding the need to keep moving muscles to balance.

And what about hawks, herons, and cormorants? They sleep while perched. Well, whether they are sleeping perched on a limb or standing on one foot, ornithologists have known for years that birds can let one side of their brain snooze while the other side remains awake and aware and balance themselves.

Unique among living animals, birds appear to have two specialized balance-sensing organs: the balance system of the inner ear (vestibular system)and an additional balance sensor located between the hips called the lumbosacral organ. The inner ear system is well developed and essential for flying movements, but the lumbosacral organ appears to be necessary or at least very helpful in terrestrial locomotion and balance while sleeping.

When sleeping, birds are subject to predation even though they might be partly hidden by vegetation; shorebirds, herons, cranes and similar birds standing in the open may be exposed to dangers. This is where the half brain function comes in – half of the brain stays awake to threats while the other half snoozes. One experiment years ago lined up four ducks in a row, each in its own glass enclosure and able to see the others. When the ducks slept, the ducks on the outside had their outside eye open and the other eye closed. Both ducks in the middle kept both eyes closed. And when a picture of a predator was shown to the ducks, the outside ducks reacted within a fifth of a second. Supporting field observations indicate that when a group of birds in a group sleep on the ground, the birds on the perimeter kept one eye open while the birds in the middle slept soundly with both eyes closed.

This half brain awake phenomenon is called unihemispheric slow-wave sleep. Aquatic mammals like dolphins and whales can do this as well but only birds can control exactly how awake half the brain is; wakefulness of one half of the brain is proportional to how open the eyelids are. So half-open eyes means that half of one side of the brain is functional, probably enough for conditions. A wide-open eye means half the brain is fully awake.

Wish that were true for me. Sometimes I’m less than half awake even with both eyes wide open.

I previously wrote a post explaining why birds don’t fall out of trees while they are sleeping. Not falling out of a tree has to do with the arrangement of muscles and tendons on the lower legs, but this explanation mainly applies to those birds in the Order Passeriformes, the Perching Birds. But not to all of them. Apparently the Eurasian Starling doesn’t use this same mechanism; it uses its innate balance to stay perched upright, even when sleeping.

And although shorebirds and flamingoes don’t perch on branches, they often sleep while standing on one leg. Turns out that shorebirds, flamingoes, and waterfowl have a mechanism of tendons and ligaments that lock in place to keep the leg rigid, thus avoiding the need to keep moving muscles to balance.

And what about hawks, herons, and cormorants? They sleep while perched. Well, whether they are sleeping perched on a limb or standing on one foot, ornithologists have known for years that birds can let one side of their brain snooze while the other side remains awake and aware and balance themselves.

Unique among living animals, birds appear to have two specialized balance-sensing organs: the balance system of the inner ear (vestibular system)and an additional balance sensor located between the hips called the lumbosacral organ. The inner ear system is well developed and essential for flying movements, but the lumbosacral organ appears to be necessary or at least very helpful in terrestrial locomotion and balance while sleeping.

When sleeping, birds are subject to predation even though they might be partly hidden by vegetation; shorebirds, herons, cranes and similar birds standing in the open may be exposed to dangers. This is where the half brain function comes in – half of the brain stays awake to threats while the other half snoozes. One experiment years ago lined up four ducks in a row, each in its own glass enclosure and able to see the others. When the ducks slept, the ducks on the outside had their outside eye open and the other eye closed. Both ducks in the middle kept both eyes closed. And when a picture of a predator was shown to the ducks, the outside ducks reacted within a fifth of a second. Supporting field observations indicate that when a group of birds in a group sleep on the ground, the birds on the perimeter kept one eye open while the birds in the middle slept soundly with both eyes closed.

This half brain awake phenomenon is called unihemispheric slow-wave sleep. Aquatic mammals like dolphins and whales can do this as well but only birds can control exactly how awake half the brain is; wakefulness of one half of the brain is proportional to how open the eyelids are. So half-open eyes means that half of one side of the brain is functional, probably enough for conditions. A wide-open eye means half the brain is fully awake.

Wish that were true for me. Sometimes I’m less than half awake even with both eyes wide open.

I previously wrote a post explaining why birds don’t fall out of trees while they are sleeping. Not falling out of a tree has to do with the arrangement of muscles and tendons on the lower legs, but this explanation mainly applies to those birds in the Order Passeriformes, the Perching Birds. But not to all of them. Apparently the Eurasian Starling doesn’t use this same mechanism; it uses its innate balance to stay perched upright, even when sleeping.

And although shorebirds and flamingoes don’t perch on branches, they often sleep while standing on one leg. Turns out that shorebirds, flamingoes, and waterfowl have a mechanism of tendons and ligaments that lock in place to keep the leg rigid, thus avoiding the need to keep moving muscles to balance.

And what about hawks, herons, and cormorants? They sleep while perched. Well, whether they are sleeping perched on a limb or standing on one foot, ornithologists have known for years that birds can let one side of their brain snooze while the other side remains awake and aware and balance themselves.

Unique among living animals, birds appear to have two specialized balance-sensing organs: the balance system of the inner ear (vestibular system)and an additional balance sensor located between the hips called the lumbosacral organ. The inner ear system is well developed and essential for flying movements, but the lumbosacral organ appears to be necessary or at least very helpful in terrestrial locomotion and balance while sleeping.

When sleeping, birds are subject to predation even though they might be partly hidden by vegetation; shorebirds, herons, cranes and similar birds standing in the open may be exposed to dangers. This is where the half brain function comes in – half of the brain stays awake to threats while the other half snoozes. One experiment years ago lined up four ducks in a row, each in its own glass enclosure and able to see the others. When the ducks slept, the ducks on the outside had their outside eye open and the other eye closed. Both ducks in the middle kept both eyes closed. And when a picture of a predator was shown to the ducks, the outside ducks reacted within a fifth of a second. Supporting field observations indicate that when a group of birds in a group sleep on the ground, the birds on the perimeter kept one eye open while the birds in the middle slept soundly with both eyes closed.

This half brain awake phenomenon is called unihemispheric slow-wave sleep. Aquatic mammals like dolphins and whales can do this as well but only birds can control exactly how awake half the brain is; wakefulness of one half of the brain is proportional to how open the eyelids are. So half-open eyes means that half of one side of the brain is functional, probably enough for conditions. A wide-open eye means half the brain is fully awake.

Wish that were true for me. Sometimes I’m less than half awake even with both eyes wide open.

And although shorebirds and flamingoes don’t perch on branches, they often sleep while standing on one leg. Turns out that shorebirds, flamingoes, and waterfowl have a mechanism of tendons and ligaments that lock in place to keep the leg rigid, thus avoiding the need to keep moving muscles to balance.

And what about hawks, herons, and cormorants? They sleep while perched. Well, whether they are sleeping perched on a limb or standing on one foot, ornithologists have known for years that birds can let one side of their brain snooze while the other side remains awake and aware and balance themselves.

Unique among living animals, birds appear to have two specialized balance-sensing organs: the balance system of the inner ear (vestibular system)and an additional balance sensor located between the hips called the lumbosacral organ. The inner ear system is well developed and essential for flying movements, but the lumbosacral organ appears to be necessary or at least very helpful in terrestrial locomotion and balance while sleeping.

When sleeping, birds are subject to predation even though they might be partly hidden by vegetation; shorebirds, herons, cranes and similar birds standing in the open may be exposed to dangers. This is where the half brain function comes in – half of the brain stays awake to threats while the other half snoozes. One experiment years ago lined up four ducks in a row, each in its own glass enclosure and able to see the others. When the ducks slept, the ducks on the outside had their outside eye open and the other eye closed. Both ducks in the middle kept both eyes closed. And when a picture of a predator was shown to the ducks, the outside ducks reacted within a fifth of a second. Supporting field observations indicate that when a group of birds in a group sleep on the ground, the birds on the perimeter kept one eye open while the birds in the middle slept soundly with both eyes closed.

This half brain awake phenomenon is called unihemispheric slow-wave sleep. Aquatic mammals like dolphins and whales can do this as well but only birds can control exactly how awake half the brain is; wakefulness of one half of the brain is proportional to how open the eyelids are. So half-open eyes means that half of one side of the brain is functional, probably enough for conditions. A wide-open eye means half the brain is fully awake.

Wish that were true for me. Sometimes I’m less than half awake even with both eyes wide open.

6 thoughts on “Sleeping Birds

  1. [Great information apparently bears repetition! LOL! ]
    I had heard about birds sleeping with one eye open, but new to me was the “unique additional balance sensor located between the hips called the lumbosacral organ.”
    Speaking of balance, why do the heads of walking birds, like pigeons and crows, move forward and back as they walk? Is it a matter of balance or is it a way to achieve depth perception with only one eye (or neither)?

    1. Yes, birds bob their heads or move them back and forth for depth perception, especially birds that spend most of their time on the ground.

  2. Oopsie, the information got a little wonky.
    Is there more that didn’t make it to the page?
    I was enjoying learning about birds sleeping, but it didn’t seem to have an ending.
    Thank you for writing on this subject!

  3. It is always a joy to receive notifications of your posts. The details about the middle aves sleeping with total trust while the ones on the outside were on ‘duty’ with the outside eyes — amazing! What trust and teamwork!

    Thank you also for the anatomy lesson in ‘Why don’t Sleeping Birds fall out of Trees.”

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