ALWAYS IN SEASON/ MIKE JACOBS: Chickadees manage the cold weather
The weather outside is frightful — but the chickadees are still delightful. How do these tiny birds endure the cold? This is a source of wonder for human bird lovers; for chickadees, it is a question of survival.
For answers, I turned to Susan M. Smith, the reigning expert on black-capped chickadees. A native Winnipegger, she's spent most of her career studying these birds. "Black-capped chickadees have a wonderful assortment of adaptations for the winter," she concludes.
The black-capped chickadee needs these, because it is a northern species. The Red River Valley is at about the midpoint of the chickadee's range, which extends almost to the tree line in northern Canada and Alaska. Winter days are short and cold almost everywhere the chickadee occurs.
The short days are a special challenge for chickadees, because they feed only in daylight. In our area, that gives them eight hours to take on calories that must sustain them through 16 hours of darkness and cold. In northern Manitoba, they have fewer than three hours of daylight.
Yet the chickadees thrive.
Chickadees extend the day somewhat, by beginning to feed when daylight is quite dim, but unlike some other northern species, including ruffed grouse, they do not feed at night.
Instead, chickadees hole up at night, literally. These tiny birds seek shelter in tight-fitting cavities, the tighter the better; so tight, in fact, that the small space crimps their tail feathers. Tight quarters help retain heat.
Chickadees regulate their internal thermometers, as well. A chickadee at rest in winter can reduce its body temperature by 20 degrees below normal.
The chickadee's feathers help the bird retain heat. Chickadees enter the winter with a full coat of new feathers, and these help the birds retain heat. They're capable of fluffing out their plumage, and this helps trap air that's warmed from the body. The difference in temperature may be as much as 70 degrees warmer at skin level than at the feather tips less than half an inch away.
Feathers are least thick on the head, and heat loss is greatest there. To protect themselves at night, chickadees pull their head into their body plumage, even under a wing. Feathers don't extend to the legs and feet, and chickadees protect their extremities, often roosting on one limb while drawing the other into the feathers of the belly.
Shivering helps, too, and chickadees are good at shivering.
All of these physical characteristics are adaptations to the cold. Chickadee social lives are adaptive, as well. The birds maintain a strict hierarchy, and dominant birds feed first. This insures the survival of the strongest birds and thus the strength of the species over the long term, even though individuals lower in the pecking order may not survive.
Chickadees don't form large flocks, and their territories don't often overlap. This gives individuals a greater chance of finding sufficient food within a territory. It's also a reason to put up a couple of bird feeders some distance apart.
Food is the fuel that heats all warm-blooded creatures, and chickadees eat a lot. Their diet is not as well suited to cold conditions as that of some other familiar species. Seeds contain a lot of oil, excellent fuel for heating a bird's body. Chickadees eat seeds, as any feeder watcher knows, but about half of their winter diet is animal fat. Chickadees come to suet; away from that supply, they often feed on animal carcasses. They also forage for insects. The chickadee is specially adapted to processing fat; large quantities build up in the body during foraging hours, and it's burned at night, leaving little reserve.
Chickadees are resident birds throughout their range. Except for occasional irruptions, they don't move around. They are not strong fliers, and this is an adaptation to cold, too, because flying consumes energy that's better used for keeping warm.
Keeping warm is the point of chickadee adaptations, and these equipped the chickadee for survival.
Smith's books are "The Black-Capped Chickadee/Behavioral Ecology and Natural History," published by Cornell University; and "Black-capped Chickadee" in the Wild Bird Guides series from Stackpole Books. She also is the author of the monograph on black-capped chickadees in "The Birds of North America" series published by the American Ornithological Union.