This entry was posted on 11/28/2006 10:42 AM and is filed under Articles by J. Baker.
When winter arrives in the northern latitudes weather dominates the conversation. It is the cold and dark of winter that makes many say “oh it would be nice to live in L.A.” Seasons down south alternate between warm and hot but up here we experience all four.
It is here, in the upper left hand corner, right around the 49o N latitude that winter comes in the right mix of cold and darkness. Any higher and it is too dark. Any lower it is too warm. To my way of thinking it would be a mistake to leave the north. As life becomes safer and more comfortable we need the tempering of winter. The black-capped chickadee too refuses to migrate south and is so tempered by winter.
Among bird populations, when conditions become extreme during this extreme season large die-offs in the tens to hundreds of thousands may occur. For example, in 1904 a wet snow storm killed at least 740,000 Lapland longspurs in western Iowa and Minnesota. Anyone who feeds or watches birds has witnessed this on a micro scale. There always seems to be more dead birds spotted during winter. But extremes are not required to threaten a bird’s life. Just regular old winter conditions of cold, short days, and lack of food conspire to make a bird’s life difficult.
Evolution has made the black-capped chickadee aware of these challenges, suggested some changes, and the black-capped chickadee has done its best to implement them. During winter, black-capped chickadees will forage for food more slowly and closer to the ground than other seasons of the year. They possess a plumage more dense than birds of similar size and molt once in late summer, insuring that their feathers will be fully capable of insulating them from the cold when winter arrives. A chickadee’s insulation is so good that it can maintain a 40oC difference between their skin and the surface of the feathers. A distance of half an inch!
A cold winter’s day will become an even colder night and the black-capped chickadee has adapted by going hypothermic. The chickadee’s body temperature will drop as much as 12oC from their normal 42 oC, reducing their overnight energy requirement. In addition to controlled hypothermia, a chickadee will burn what fat they stored during their day time foraging by shivering to generate heat. Finally, the black-capped chickadee will roost in whatever hole or crack in a tree it can find. There it finds refuge from the heat sapping wind and rain.
With all these cold weather adaptations the black-capped chickadee still appreciates the goodies we set out at the feeder. Sure, they have the skills to survive winter on what insects it can glean from the bark and branches of trees, but when conditions become extreme, birds foraging in an area with food supplementation show significantly greater over winter survival. Besides what they don’t eat then, they will take to their roost for breakfast!
Winter tempers the chickadee by shaping its behavior and physiology so it may survive. Our technology protects us from these winter risks. However, to the observer of nature, winter can temper our attitude. It helps us understand that this is a diverse world, that life is a fragile state, and adaptation is a required characteristic for survival. I would like to think that the chickadee knows spring is coming and if they can make it through the challenge of winter, they can look forward to the insects of spring.
As always, I would like to hear what you have to say. Please feel free to leave a comment.
