Birds utilize a number of behavioral adaptations that afford them some protection from frigid air such as we have been experiencing lately. They include sunning (turning their backs to the sun, exposing the largest surface of their bodies to the heat), shivering, tucking (placing one foot up inside feathers while standing on other leg, or squatting to cover both legs and feet with feathers; tucking their bill into their shoulder feathers and breathing air warmed by their body), roosting together in small groups (often in a small cavity, so as to conserve heat) and, most obvious of all, fluffing themselves up (creating air pockets that are warmed by body heat).
While feathers serve many purposes, from helping to attract a mate to providing camouflage, one of the most important jobs they have in winter is to keep a bird warm and dry. A bird’s body heat (the average bird’s body temperature is 105 degrees Fahrenheit), warms the air between its feathers. Birds fluff up in the cold to trap as much air in their feathers as possible, as the more trapped air, the warmer the bird. They can appear two or three times larger than they appear on a 32 degree day. This insulation is effective because it also is a barrier to water. The oil that birds apply to their feathers when they preen serves to waterproof the feathers. (Photo: Dark-eyed Junco)
This week those of us in the Northeast have been inundated with dark-eyed juncos, often referred to as “snow birds” due to their presence in much of the U.S. only during the winter months. Although this member of the sparrow family breeds here and is found year-round in New England, over most of the eastern U.S. juncos appear as winter sets in and then retreat northward each spring. Many of the juncos that we are seeing now are transitory migrants on their way to Canada and the Arctic to their breeding grounds. They will remain there until next fall, when we will experience a similar influx. Research has found that males migrate earlier than females, and that females tend to migrate further south than males. The timing of this migration is regulated primarily by the lengthening spring days.
Countershading is a common color pattern in animals in which the upper side of the animal is darker than the lower side. This color pattern provides camouflage for the animal when viewed from the side, above or below. The counter shading pattern balances the sunlight on the animal’s back and the shadow beneath the animal so as to blend the animal’s side profile with its surroundings. In addition, when viewed from below, a counter-shaded animal with a light belly blends into the light coming from the sky above. When viewed from above, the darker back of a counter-shaded animal blends into the darker ground colors below. Birds (which spend a considerable amount of time in the air) such as this dark-eyed junco, as well as marine animals often exhibit countershading.
In New England, Dark-eyed Juncos typically have two broods in a summer. The second-brood nest in the photograph contains the first of probably four or five eggs which are laid one day at a time. The egg lies on a soft lining made from the hair of a White-tailed Deer. Unlike most songbirds, Dark-eyed Juncos build their nests in a wide variety of sites, from the ground up to eight feet high in trees. Often they are in a small cavity on a sloping bank (well hidden by surrounding grass), under a protruding rock or among tree roots. But they’ve also been found under fallen tree trunks, on supports underneath houses on stilts, in barns or lofts between hay bales, in vines on the sides of buildings, on window ledges and light fixtures and in hanging flower pots. It’s not unheard of to find a Dark-eyed Juncos relining the old nest of an American Robin.