Great Blue Heron (Photo by Don Reimer)
Great Blue Heron (Photo by Don Reimer)
One recent cold morning, I scanned an ocean cove where several species of ducks and a congregation of Canada Geese floated nonchalantly in the ice-skimmed 46 F degree water.  It had snowed overnight and the ducks’ backs and heads were frosted with a solid coating of snow. By contrast, I wore a wool winter cap, insulated boots and three layers of warm protective clothing to shield my outer core from the frigid air and wet falling snow.

For many species, migration would seem like the safest alternative to wintering in the North, an easy escape clause. But migration presents a huge and risky undertaking that requires accumulated fat reserves of 50% of body weight for sustained flights. Factoring in potential dangers of predator attacks, erratic weather systems and uncertain food availability, migration is not always an easy-out solution. For species that utilize insect matter and open water environments for survival, however, migration is a necessary risk that prompts them south by late fall.

How do wintering birds survive and prosper under such demanding weather conditions? For waterfowl, dense layers of water-repellant feathers preserve equilibrium of inner body heat. Natural oil in the feathers adds more protection. We should be duly impressed by wintering loons, ducks and alcids that eat and sleep in the turbulent ocean day and night. These web-footed birds also reduce heat losses to some extent by tightly closing the fleshy foot webbing, thus minimizing heat-leaking surfaces.

Through observing gulls in a parking lot, you may notice some of their winter tactics for staying warm. Gulls often stand on one leg, reducing heat loss by a factor of one third; tucking their bare bill into body feathers conserves an additional third of vital energy stores. Birds maintain higher body temperatures than mammals, averaging 105 degrees F. With their greater body mass, larger birds may have an easier time withstanding extreme temperatures.

Smaller songbirds face winter survival challenges because they have less body mass to produce heat. Consider the dilemma of that immature male Bullock’s Oriole that has visited a Camden bird feeder since November.  With reliable daily food resources of fruit and mealworms, staying put is probably his smartest option at this point. The oriole was seen tucking one leg into his belly feathers to stay warm. This may be a new and unaccustomed behavior for a neo-tropical migrant that typically dwells in perpetual summer.

Certain species are specialized and adapted to life in the cold. Arriving from high Arctic regions, flocks of swirling Snow Buntings are a prime example. Buntings have stubby conical bills that are less susceptible to major heat loss. While feeding on weed seeds on the ground, Snow Buntings adopt a low, crouching posture that reduces wind exposures to the body and limits the volume of cold air striking their legs.

Some birds grow additional feathers as cold weather ap-proaches. American goldfinches, which have about 1,000 feathers during the breeding season, molt in late summer and grow about 2,000 new ones for winter insulation.

Other winter strategies? In September, Ruffed Grouse grow extended scales on their toes that function as snowshoes in deep snow. Grouse also burrow into powdery snowdrifts, fashioning a snug snow cave on those brutal winter evenings. Many smaller birds seek the protection of tree cavities during the overnights, where even a temperature rise of a few degrees can make a life-sustaining outcome.  Groups of tiny Golden-Crowned Kinglets are known to huddle in cavities to share their collective body heat, while chickadees lower their internal thermostat at night by entering a state of induced torpor.