The tube feeder is glazed with last night’s sleet and freezing rain, a thick coating of ice that molds like shrink-wrap to the bird buffet just outside my kitchen window. The sunflower seeds are encased, as is the suet cake hanging nearby. It’s just after 6 a.m., well before sun-up, but in the gray light a chickadee lands on the pole, lets itself slide down the slanting arm to the feeder, and starts pecking at the rime. I wrap my chilly hands around the coffee mug and admire the bird’s brisk efficiency as it excavates a seed, holds it across the metal rim of the feeder, and cracks through the hull to get at the oil-rich kernel. “You could clear the front steps of ice, too, if you felt so inclined,” I murmur. The chickadee grabs another seed and flies off. Oh, well, never hurts to ask, I guess.
The TV is filled with news of school closings, warnings of treacherous driving on I-95, and statistics on current power outages. Meanwhile, two other chickadees are working on the suet block, hammering at the ice to get to the peanut butter-enriched animal fat. And what I am thinking is what I often think on mornings like this: How did we humans ever get the idea that we are the apex species, when less than a quarter inch of ice brings our built universe to a crawl? By contrast, consider the superb adaptations of the chickadee to the ugliest conditions Old Man Winter can throw at it.
First, the birds are marvelously industrious little buggers. The average chickadee needs to eat the equivalent of 250 sunflower seeds’ worth of energy every day, not a problem during the summer when there are nice, juicy insects, caterpillars, and spiders to gather. When those food sources are gone, however, the bird must still make up the energy requirement. One of the chickadee’s survival tools is hoarding food during the fat months of the harvest. It has been estimated that a single bird will cache between 50,000 and 80,000 seeds in the autumn, the treasure trove spread over many locations to which the chickadee can unerringly return when those food resources are needed. In fact, the area of the little bird’s brain dealing with spatial awareness is nearly double the size of that of other species. Also, apparently the neurons in that area die and are replaced each year, specifically to perform this function, presumably so the bird can’t confuse last year’s locations with this year’s, which could be a life-threatening mistake. Since half the time I can’t remember where I left my reading glasses, this is amazing to me.
Another adaptation which makes chickadees able to thrive in winter is that they replace their feathers at the end of summer. When cold weather comes, therefore, their plumage is relatively new, up to 25% denser than that of birds which don’t molt at that time. If you’ve seen a hugely fluffed-out chickadee on a tree branch on a -10 degree day, you’ve seen this nice, thick, down comforter in action. Those high-lofting feathers conserve body heat.
The third way chickadees make it through our long, frigid nights is the birds’ careful selection of winter roosting places. Unlike other species, chickadees do not roost communally, with several birds crowding into an old nest box, for instance, to share warmth. Instead chickadees roost individually, their own body heat the only source of warmth. Often they will choose a birch, alder, or willow in which to site a roost, those woods being soft enough that the bird can excavate a tiny chamber, its entrance sometimes only the size of a quarter and most often on the side of the tree facing away from prevailing winter winds. As in all real estate, location, location, location is the name of the game for survival. If the chickadee can find a nesting hole abandoned by a downy woodpecker, a species which is close to the black-cap’s own size, so much the better. The digs are dug, the cable TV is already hooked up, and there may even be a morsel of two of suet stocked in the fridge.
It is the final adaptation chickadees have made that most amazes me, however. No matter how hard a bird works to consume calories during our short winter days, it must still survive a fifteen hour fast every night (up to eighteen hours in Alaska and northern Canada), just when the temperature is at its coldest. The bird’s normal body temperature is about 108 degrees F. The caloric reserve just isn’t going to last long enough to support that. So the chickadee has evolved to lower its body temperature to about 85 degrees at night, entering a state of hypothermia to reduce its metabolism. One biologist at the University of Alaska-Fairbanks who studied the phenomenon reported that the chickadees she studied stuffed themselves during the day to gain an additional 10% or more of their body weight, then used that excess fat to shiver themselves warm in their hypothermic state every night, losing the entire amount of weight before morning. She compared this to a 165-pound man spending a frigid night outside and shivering off fifteen pounds by morning.
Obviously, when that bird comes out of its hidey-hole in the morning, it needs to eat now, whether from one of its food caches or from my feeder. Happily, my black-oil sunflower seeds and suet supply the chickadee’s needs, and the sight of my small, indomitable neighbor supplies mine.
Information in this post is drawn from www.nwf.org/gardenforwildlife/12-01-2007