The average body temperature of a bird is 105 degrees Fahrenheit or 40 degrees Celsius. There is some slight variation among species. Birds are warm-blooded, which means that their bodies maintain the same temperature despite the temperature of the environment.
In cold temperatures, birds sometimes struggle to maintain a consistent internal temperature. Small birds have the most difficulty because they have less mass to produce heat. Feathers provide good insulation, and the oil covering on them adds protection. Some birds grow additional feathers as cold weather approaches. The scales on the legs and feet of birds also guard against cold. In addition, birds that spend winter in cold climes prepare during the fall by eating large amounts to add extra layers of fat.