If the majority of an animal’s body heat derives from its own metabolism, it is an endotherm. Mammals and birds are endotherms. There are some species of reptiles, fishes, and insects that are also endothermic. Endotherms have many adaptations to maintain their body heat. The beautiful macaw pictured above, for example, has a very efficient circulatory and respiratory system. This helps to support its high metabolic rate. The bird’s colorful feathers aren’t just for show, either. Among other things, feathers act as insulation to help birds stay warm.