However this uses energy quickly. The most obvious way animals keep warm is by their fur and feather coverings. Birds like the little chickadee or titmouse stay warm by fluffing up their feathers. This and the layer of down underneath traps warm insulating air to protect them and keep them warm. It s kind of like when people layer their clothing to keep warm.
Warm air is trapped in each of the layers providing a buffer to the cold.
Birds will further reduce heat loss while breathing by tucking their bills into their back or breast. The worst enemy of birds in winter is moisture in the form of rain, sleet or freezing rain. Birds have an oil gland on the top base of their tail enabling them to waterproof their feathers to some extent by preening and spreading the protective covering. This is true of certain mammals as well. Mammals have under-fur that does somewhat the same thing, traps warm air to provide an insulating layer.