Last year at about this time I read Winter World (2003) – a remarkable book by Bernd Heinrich on the wintering habits and adaptations of a variety of organisms. The example which has stuck with me is that of the Golden-crowned Kinglet. As the winter approaches and bird song in the woods diminishes these birds and their high-pitched calls and presence bring cheer, hope and awe.
While relatively common, Golden-crowned Kinglets are not the easiest birds to see. They are small, drab, constantly moving and do not visit bird feeders. (Anna’s hummingbirds, which survive winters here, are smaller than Kinglets, but are dependent on sugar feeders.) The Golden-crowned Kinglet has a white eye stripe, which distinguished it from the Ruby-crowned Kinglet, which has a white eye ring. Kinglets are named “Regulus” (little king) for the golden and red crowns, which are difficult to see, but the bird may flash it on occasion. The crowns of the males are yellow with a small amount of red in the center, while that of the female is pure yellow.
Golden-crowned Kinglets forage continually from dawn to dusk, hovering at branch tips feeding on what appear to be invisible insects and eggs. Heinrich, who has a reputation as a persistent and somewhat unorthodox researcher, (he once ran after a bumble bee all day to study its foraging; he is also an ultra marathoner) finally discovered that the Kinglets in his Maine woods feed on the tiny larvae of the one-spotted variant moth (Hypagyrtis unipunctata) which overwinter on tree branches and not underground like related species. Without the winter adaptation of the larvae the Kinglets would have no chance. If one values the Kinglet one must also value the moth. With a full belly they might top out at 6 grams of which they might burn twenty five percent just to get through the night.
At dusk a small group may settle under dense brush and huddle for warmth. This explains the calls they make which helps keep the flock together. If they are huddled with two or three others the chances of surviving the night are greater. Huddling together reduces the surface area exposed and in a way increases the mass of the kinglet. Other behaviours such as fluffing out their feathers to increase the insulating air space around them and burrowing their beaks and heads into their feathers also reduce heat loss. The beak and eyelids are not insulated so lose heat faster than the rest of the body. The legs too are uninsulated, but heat loss here is minimized by a reduction in blood flow and perhaps a countercurrent heat exchange, which keep the legs and feet cold. (Incidentally heat can be increased to legs during breeding season– a physiological feature which may assist in egg incubation.)
An idea posited by German biologist Karl Bergmann in the mid 19th century suggests that the organisms in northern climates are larger than organisms closer to the tropics. The reasoning is that a larger body has a greater mass to surface area ratio and thus the animal is better able to conserve heat and survive the cold. This may generally be the case, but the Kinglet is certainly an exception to the rule. They are year round residents as far north as Alaska. That any of these tiny birds can survive sub-zero temperatures is incredible. By doing the right things and with a bit of luck on their side enough will survive to mate, nest and perhaps raise two broods to repopulate the woods next year.
Jay Rastogi is a naturalist, horticulturalist and educator living in Yellow Point.