Black-capped chickadees are found throughout Minnesota and well into Canada and Alaska. We see these agile, seemingly cheerful birds outside no matter what the weather. Chickadees and other birds have adaptations to help them deal with the cold. Without these adaptations, the 5-inch-long chickadee, with the core of its tiny body less than an inch from the outside air, would freeze almost immediately.

Sometimes chickadees shiver. Shivering allows them to make short-term adjustments to cold; it is the main way they increase their heat production while at rest. Shivering converts muscular energy into heat, but this used energy must soon be replaced through eating. To maintain their high heat and energy production, chickadees eat energy-rich foods such as insects and seeds.

Chickadees are also able to gradually drop their body temperatures during inactive times until they reach a regulated condition of hypothermia. In this condition they shiver just enough to maintain their colder state. Their normal body temperature is 107 degrees, but now it can drop as many as 18 to 22 degrees, providing energy savings of close to 20 percent. This diminishes the temperature variance between the air and the birds' bodies, and they lose less heat.

Primarily, heat loss in birds is diminished by their coat of feathers, which they can fluff out for greater insulation. Birds have tendinous lower legs and feet rather than exposed flesh. Their bills are made of horn, not skin, and give up little heat. They have no projecting fleshy ears or tails from which heat would be lost. Also, bird body temperatures are higher than those of mammals.

Jim Gilbert's Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.