Female Northern Cardinal in the snow

Thermoregulation

Non-migratory birds that winter in place stay warm on cold days by shivering, fluffing feathers to create heat-trapping air pockets, and hunkering down in sheltered roosting spots, sometimes with fellow birds.

Beaks lose more heat than legs, but both can be tucked into more protected, feathered bodies. Birds can further prevent heat loss by restricting blood flow to beaks and legs, and waterfowl swimming in cold water or species that stand on ice reduce heat loss by using a countercurrent heat exchange in their legs.

    Some bird species enter a short-duration hibernation called torpor in response to the cold, meaning their metabolism slows and their core body temperature lowers. These heterotherms (animals with variable core body temperatures) include hummingbirds, which can enter daily torpor to conserve energy. Research comparing hummingbird species showed that torpor is used more routinely by smaller species than larger ones which enter torpor only in emergency situations.

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