Just after sunset, with fading light and falling temperature, wave after wave of Canada Geese circled our cove and gracefully landed. They joined a raucous flock of geese, perhaps 500 or more, apparently judging the cove to be a safe haven for the night. But with all the honking I wondered if any, myself included, would ever be able to fall asleep. With darkness, however, they did quiet down, except for the occasional honk from a vigilant sentry goose proclaiming all is well.
As one ages sleep patterns become an issue, and sometimes even a topic of conversation and concern. Being a curious birder I decided to do a little research, emphasis on little, as to the sleeping habits of our feathered friends. What’s their sleep pattern, how much do they need, where do they go at night, can they sleep while flying, etc.? I also scanned my photo archives looking for pictures of sleeping birds. Unfortunately I usually delete pictures of birds with their eyes closed, but did find a few suitable for this post.
On my bedside nightstand there is a fascinating book by Matthew Walker entitled “Why We Sleep”. It’s mostly about humans but does include a great chapter about the evolution of sleep. According to the author a biologic sleep requirement must have evolved very early, as all animals, even insects, demonstrate sleep cycles. You can confirm this with the characteristic brain waves on the EEG’s of sleeping animals and by periodic cycles of non-arousal of small insects.
Although all animals require some sleep, the amount and style vary considerably. Walker states that the length of the restorative sleep requirement is determined by the complexity of the animal’s nervous system. Both the length and type have evolved separately for every species and are balanced by the equally important need for wakeful hunting, eating, nest-building, and blog writing.
We are all familiar with the two types of sleep, REM and non-REM, identified by their characteristic brain waves. It’s interesting that REM, the shallower sleep stage associated with dreaming, only occurs in mammals and birds. It is, therefore, a later creation in the evolutionary sequence. I consider it an “eye opener” to think of birds actually dreaming.
Although there are similarities between avian and human sleep, there are also many differences. Birds demonstrate hemispheric sleep, the amazing ability to let half the brain sleep while the other half stays wide awake, perhaps as a defense for lurking predators. At some point this split reverses and the other half falls asleep. It’s interesting that this hemispheric sleep only occurs with non-REM sleep; REM for some reason, requires total brain participation.
Frigatebirds are amazing seabirds that can stay aloft without landing for up to two months. They have one major deficit–they cannot swim. If forced to land at sea they quickly become water-logged and drown. So curious Niels Rattenborg and others from the Max Planck Institute for Ornithology figured they would be the perfect bird to evaluate for in-flight sleep.
Rattenborg fastened EEG leads to the skulls of 15 frigatebirds and attached a device to monitor flight speed. The study confirmed that birds do indeed sleep while flying, but not in the expected manner. They slept only in short bursts of 10 seconds and only for a total of 45 minutes each day, a much shorter duration than their sleep cycle on land. They also only used hemispheric sleep while flying, and only slept while gaining altitude in a thermal. They were completely awake and alert in every gliding descent, perhaps to avoid a lethal crash landing at sea.
Birds assume many different sleeping positions on land, but I’ve not yet seen one on its back with feet pointing heavenward. Shorebirds sleep standing up, often on one leg, and usually facing into the wind. Night herons, owls, and woodpeckers sleep perched upright. Their leg muscles in a relaxed state result in a clenched claw, firmly grasping the branch. Many birds such as the nighthawks sleep horizontally, while some parrots sleep hanging upside down in a bat-like manner. Many cavity nesters seek out a vacant cavity for the night.
Birds, like humans, are susceptible to sleep deprivation. Walker reports that the U.S. government has spent millions investigating the sleep pattern of the lowly White-crowned Sparrow. If you deprive this bird of sleep during the season it would normally be migrating, it experiences no ill effects. But similar sleep deprivation at any other time results in catastrophic physiologic brain and body dysfunction.
I’m not sure how they deprived the little bird of sleep; perhaps with bright lights and continuous Barry Manilow songs at high volume. In any case, this bird has apparently evolved some protective mechanism for sleep deprivation that the U.S. government would love to uncover.
Have you noticed how difficult it is to sleep the first night in a new hotel and bed? I now believe this is a throwback to my evolutionary past. Is there a Sabre-toothed Tiger lurking in the bushes or a Wooly Mammoth lumbering past my cave? Just like the birds I require safe sleep, but haven’t yet mastered that hemispheric trick. I guess I need that sentinel goose, standing guard and signaling all is well.