Temperature Regulation Cold Climates Animals that live in water usually take on the temperature of the water, which is usually stable. Terrestrial reptiles keep their body temperature stable by absorbing solar radiation during the day. At night they seek shelter to keep warm and to protect themselves during the inactivity that results when they are cooled. Animals that obtain heat from external sources are called ectotherms. Mammals and birds are called endotherms, because they maintain a constant body temperature through metabolism and regulation.
Birds use their feathers to protect their bodies.
They also migrate to warmer climates. Mammals reduce heat loss in many ways. Below are a few examples.