Birds migrate. Bears hibernate. Everyone knows this, even relatively uneducated toddlers. Hence the multitudes of kiddish jokes about it.
At some point in the long, cheesy realm of childhood, I would pick up a joke book containing the question "Why do birds fly south for the winter?" The predictable answer would be, of course, "Because it's too far to walk."
This joke, which is already annoyingly stupid, adds to its lowly status by being a very scientifically inaccurate joke. Odd specificity of structures in bird's legs make a good portion of migrating birds restricted to hopping pogo-stick movements instead of a robin-like stroll. This really bothers no one except birders (It's as bad as calling an egret a *gasp* crane, which means automatic death by binocular clubbing for the poor soul who utters those words in the birding community).
Yellow-rumped Warblers are migratory. They do not walk. They hop. Gosh, get it right, joke books.
Why do birds fly south for the winter?
Because it's too far to hop.
But this post is not about how far off the mark our favorite childhood jokes are from scientific truth. It is about the amazing abilities of birds.
Birdwatchers entering the initiation into becoming a birder will have to possess the knowledge of which birds are migratory and which are residents to pass the test. Those crucial pieces of information should be modified to include which birds are migratory, residents, and...wait for it... hibernators.
Quick quiz: which of these colored birds are very migratory, which are partially migratory,and which are residents? No looking at the field guide. This should be an easy one for you birders. Answer in the comments!
A true ornithologist would, at this point, exclaim, "Hibernators? There's only one widely known one. You don't know what you're talking about."
Let me explain hibernation in birds a bit, at risk of boring the reader to sleep. It's difficult to pin an exact definition of hibernation, but the general gist of it is that hibernation is an extended period when an extremely deep "sleep" (torpor is considered a scientifically "incorrect" description) is the overwhelmingly dominant way the animal spends its time.
Many birds, including hummingbirds, undergo torpor sparingly or during the night only. The Common Poorwill is the most widely known bird to shut down, hide in a crack, and dream the majority of the winter away. Mostly in the desert, mind you. In the desert. The Common Poorwill is no bear of the bird world.
Hummingbirds are rather famous for their awesome torpor abilities.
Almost nada birds have been regularly and definitely recorded to hibernate in areas where snow is expected every winter. The reason why is pretty reasonable: Most birds other than poorwills' bodies are not efficient enough to undergo a long period of torpor in such chilly conditions and be able to arise weeks or months later ready to eat its fill, or go around singing, or whatever birds would do when awakening from torpor.
That is, no regular and definite records.
Ornithologists tend to be slight humbuggers when it comes to accepting records and making conclusions. Any birder who has had an annoying email escalade with a local eBird reviewer or doubtful Listserv addict will know this all too well.
Is there sufficient evidence to suggest, that, in times of dire circumstance, birds besides the Common Poorwill could enter hibernation--and make it out alive?
Of course, there's been the occasional swift or dove found limp, cold, and torpid out during the winter. Is this enough to suggest that birds are, shrouded from human observation, having bouts of hibernation (is that even possible? Bouts of hibernation? That sounds so unscientific. Hell, this entire blog post is. I shouldn't have put in that stupid joke. It ruined the entire thing).
You would think that the most likely candidates for hibernation ability would be the relatives of the Common Poorwill. Not so. In fact, it seems that most of the contenders in the hibernation game are doves or small birds.
Columbidae (the family that includes the lowly Mourning Dove and Rock Pigeon/Dove/Whatever-it-was) frequently fall into long periods of torpor triggered by lack of food. That's technically not hibernation, but before all you ornithologists jump all over this post, it's close enough when you consider most other birds simply just fly, or hop, south for the winter instead of dealing with a lack of food that could be brought on by Christmas chills.
Many other birds also come exhilaratingly close (well, exhilarating to aspiring ornithologists anyway) to cutting the dove-pigeon standard. Sustainable large drops in metabolism leading to brief torpor in relation to temperature seems to be a pattern in various small birds. This list is mainly comprised of tits. A night of torpor is probably the closest most passerines will ever come to cutting it to hibernation.
All in all, the Common Poorwill may be the only definite bird to have a sort of light hibernation. Okay, fine, ornithologists, you can come at me now for saying "hibernators," instead of "hibernator."
Stay warm for the CBC (No, that does not stand for Canadian Broadcasting Corporation, you hockey fan, eh)
-chiccadee
A fine specimen of a crane.
