Birds' Sleep Patterns: Standing Up In Rem Sleep?

Birds have two types of sleep: rapid eye movement (REM) sleep and non-rapid eye movement (non-REM) sleep. These sleep cycles are similar to those of mammals, but there are some differences. Non-REM sleep in birds averages around two and a half minutes, while REM sleep is about nine seconds. Birds can also sleep with one-half of their brain awake, a phenomenon called unihemispheric slow-wave sleep. This allows them to remain alert to potential predators while still getting some rest.

Birds can also stand during REM sleep, which is when most muscle tone is lost. This is not the case for most mammals, which usually lie down to sleep. Birds are able to maintain their balance while standing during REM sleep.

Birds are also able to sleep while flying. Great frigatebirds, for example, can sleep while soaring and gliding, but not while flapping. They can sleep with both brain hemispheres or with just one hemisphere at a time.

Birds have REM and non-REM sleep cycles, but these are much shorter than in humans

Birds have two types of sleep: rapid eye movement (REM) sleep and non-REM sleep. These sleep cycles are similar to those of mammals, but much shorter.

REM sleep is believed to have an important effect on motor functions and memory storage. During REM sleep, birds' eyes move rapidly behind closed eyelids, and brainwaves oscillate rapidly. Most dreams occur during this sleep stage.

Non-REM sleep is a form of deep sleep, during which brainwaves pulse more slowly. Non-REM sleep is homeostatically regulated, meaning that the amount of non-REM sleep can be recovered by sleeping more intensely.

Birds can quickly transition between states of wakefulness, non-REM sleep and REM sleep. They can also sleep with one half of their brain awake, a phenomenon known as unihemispheric slow-wave sleep. This allows birds to remain alert to potential predators while still catching some sleep.

Birds can adjust how much of their brain is asleep by how wide they open or close their eyes. The amount of sleep necessary to function can vary by species. For example, male pectoral sandpipers sleep very little during their three-week breeding season, and some have been observed to give up 95% of their sleep time during this period.

Birds' sleep is influenced by factors such as the presence of predators, perch height, and exposure to artificial light at night.

Birds can sleep with one half of their brain awake, a phenomenon called unihemispheric slow-wave sleep

Birds have two main types of sleep: rapid eye movement (REM) sleep and non-REM sleep. Both cycles are shorter than those of humans. Non-REM sleep averages around two and a half minutes, and REM sleep is about nine seconds. Birds can adjust how much of their brain is asleep by how wide they open or close their eyes.

Unihemispheric slow-wave sleep has been documented in species across the avian tree of life, from ducks and chickens to parakeets, falcons, and sparrows. A few years ago, researchers from the Avian Sleep Group at the Max Planck Institute for Ornithology studied this phenomenon in frigatebirds. These seabirds are master gliders and soarers over the open ocean. Frigatebirds routinely fly for days at a time without ever landing on the sea surface. In fact, they can't swim or float and never land on water if they can help it.

The researchers connected tiny EEG devices to 15 female Great Frigatebirds in the Galapagos Islands. These devices measured the birds' brainwaves and were connected to little data logger backpacks. Data were collected on non-stop flights of up to 10 days.

This study had a couple of cool results. First, it turns out that frigatebirds do indeed use unihemispheric slow-wave sleep on their epic flights. This was long predicted but never proven until this study. Pretty awesome.

Second, these birds sleep less deeply and much less often while flying than when perched on land. This result surprised the researchers. While flying, the birds sleep about 45 minutes a day on average, which is less than 10% of the time they sleep on land. So even though frigatebirds can cruise the skies using unihemispheric slow-wave sleep, they don't use it very often on these long flights. It seems they need to be fully alert most of the time.

Birds are not alone in having the superpower of sleeping with one eye open. We've known for a while that many marine mammals use unihemispheric slow-wave sleep. These include manatees, seals, sea lions, dolphins, and possibly some baleen whales.

There's even a wee bit of evidence of some asymmetry between the hemispheres of human brains during sleep. One recent study showed that when a person sleeps in an unfamiliar place for the first time, there is a weak, but statistically significant difference in responsiveness between the two halves of their brain. And they sleep less deeply overall.

Birds do not lose muscle tone when in deep sleep, unlike humans

Birds have two types of sleep: rapid eye movement (REM) sleep and non-REM sleep. During REM sleep, birds' eyes move behind closed eyelids, and their brainwaves oscillate rapidly. During non-REM sleep, brainwaves pulse more slowly, and this is considered "deep sleep".

Birds' sleep consists of periods of eye closure, interrupted by short periods of eye-opening. During these short periods of eye-opening, electroencephalographic (EEG) studies indicate that the birds are still sleeping; the voltage level in the brain is identical. Birds restore their arousal thresholds during sleep.

Birds can also engage in unihemispheric slow-wave sleep, where one half of the brain is in slow-wave sleep, while the other half appears to be awake. This type of sleep has also been seen in dolphins and whales. The organism is typically able to keep one eye open during this process, which allows added vigilance in high-predation environments.

Birds can adjust how much of their brain is asleep by how wide they open or close their eyes

Birds have the ability to adjust how much of their brain is asleep by how wide they open or close their eyes. This is known as unihemispheric slow-wave sleep, where one half of the brain is in slow-wave sleep while the other half appears to be awake. This type of sleep has also been observed in dolphins and whales.

Unihemispheric slow-wave sleep is thought to have evolved in aquatic mammals because they must return to the surface for oxygen, and in birds to help them avoid predation. Birds can keep one eye open during this process, allowing them to be vigilant in high-predation environments.

Birds that sleep in flocks tend to experience an increase in overall eye-closure time and a decrease in the amount of eye-opening. In the presence of a predator, birds exhibit higher levels of individual vigilance and an increase in open-eye sleep, reducing the active-sleep component of their total sleep time.

Birds that sleep on lower perches have been found to experience a reduction in the number and length of REM sleep episodes, as REM sleep is a less reactive form of sleep that would place them in more danger.

Light is one of the more common threats to sufficient sleep for birds living in anthropogenic environments, known as "artificial light pollution at night" (ALAN). ALAN eliminates darkness, which is necessary for rest, and can impact birds' circadian rhythms and sleep patterns.

Birds can sleep standing, perched, roosting, lying down, swimming or hanging upside down

Birds can sleep standing, perched, roosting, lying down, swimming, or hanging upside down.

Standing

Birds can sleep standing up, but not all of them. It depends on the species. Most birds that sleep standing are those living in the wild, where the danger is typically greater. The standing position keeps the birds' muscles ready to fly and helps them stay alert without going into a deep sleep, which can cause their death if a predator strikes. Some birds also sleep standing up because that's the only way they can get comfortable. For instance, flamingos mostly live in caustic salt falls. There's nowhere they can sit or lie around, so they must sleep standing up.

Perched

Most bird species sleep standing up, including owls, hawks, and hummingbirds. Owls have special tendons in their legs that keep them clamped against the tree branch they sleep on. That way, they can rest for the night, and at the same time, clamp themselves on the tree for security and to avoid falling.

Roosting

When birds settle down to sleep, it's called "roosting," and the main things they're looking for are safety and warmth. Songbirds have to keep off the ground to avoid cats and things, and out of the open to avoid owls. Dense brush or foliage does fine. Bigger birds have more options and can sleep on the water, on a branch, or even just right on the ground.

Lying Down

Waterfowl and shorebirds sleep near the water. Ducks often stand at the water's edge or on a partially submerged stick or rock and tuck one foot into their body, much like birds do on perches.

Swimming

Some birds can sleep while swimming. There is evidence that the Alpine Swift can fly non-stop for 200 days, sleeping while in flight!

Hanging Upside Down

People raising pet parrots are probably familiar with the upside-down sleeping position. A lot of parrots, called bat parrots, sleep in the odd position to protect themselves from predators. They sometimes bathe in the same position, and some species, like African grey parrots, hang out casually while upside down. They'll play around and relax as if they're not at the risk of falling anytime.

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