Mewsings from Millie
I recently heard two of my people talking about their up-coming birding trip to Ecuador. They were discussing the possibility of having altitude sickness and that got me to wonder - why don't birds ever suffer from this malady? Most songbirds migrate below 1,200 feet but some shorebirds often fly above 10,000 feet and raptors have been recorded at well over 20,000 feet! Humans can begin to feel symptoms of altitude sickness at 8,000 feet so why don't these birds get sick?
Well, I found out that birds' respiratory systems are very different from those of mammals. Although their lungs are very small, their physical make up allows the oxygen to be diffused over a large surface area and the barrier between the oxygen and the blood is very thin. Birds also have a series of air sacs that work like bellows to continuously move air through the lungs. This maximizes the amount of fresh air going through the system and oxygen exchange is almost continuous.
Then I thought more about these birds and the long flights they make. They must get tired! Do they sleep? How much do they sleep? Do birds yawn?
Yawning occurs in just about every vertebrate animal yet there is no conclusive evidence as to why this behavior is exhibited.
In contrast to what most people believe, yawning does not increase oxygen to the brain in humans nor does it help keep humans awake or prepare their brains for sleep.
Yawning in birds could serve as a thermoregulatory behavior. Birds yawn more in warmer conditions and it doesn't mean they are feeling drowsy.
As far as sleep goes, birds don't sleep for long periods of time like mammals do. Birds seem to sleep off and on during the day and night when they are not busy foraging, avoiding predators, tending to young or defending a territory.
Birds "sleep" in a semi-alert state in which half of the brain remains awake. No deep sleep REM dreams for them! This type of sleep is called "unihemispherical sleep". This allows birds to stay vigilant and detect predators. Ducks are often seen resting on the water with one eye open and one eye closed. They are "sleeping".
Birds also sleep this way during migration. Most songbirds migrate at night but then they must actively forage for food during the day. Napping while flying with one eye open is just another example of the amazing lives of birds.
Until next time,
The Muse of Mews
- A tip of a whisker to Birdwatching magazine