homeothermic

Homeothermy is the physiological ability of an organism to maintain a relatively constant internal body temperature despite variations in the external environment. In most discussions, it is closely linked with endothermy, the generation of metabolic heat, but the concepts are not perfectly identical: an animal can regulate temperature through insulation and vasomotor changes without relying solely on heat production, and some species may display regional or partial heat retention.

Birds and mammals are the classic homeotherms. Their core body temperatures are held within narrow ranges—typically around 36–38°C for many mammals and about 39–41°C for birds—across a broad range of ambient temperatures. This stability supports sustained metabolic activity and, in many cases, high locomotor performance.

Mechanisms underlying homeothermy include metabolic heat production, such as shivering and non-shivering thermogenesis via brown adipose tissue in many mammals, along with insulation from fur, feathers, or fat. Heat exchange is also regulated through vasomotor control of blood vessels, reducing or increasing heat loss as needed. Behavioral strategies, including basking in the sun, seeking shade, burrowing, or huddling, complement physiological processes to maintain a stable internal temperature.

Evolutionarily, homeothermy is associated with higher and more constant metabolic rates, enabling activity in diverse environments and enabling capabilities like sustained flight in birds. These advantages come with trade-offs, notably higher energy requirements and competition for food resources, as well as vulnerability to overheating in extreme heat. In scientific discussions, the term is also used to explore the thermal biology of extinct lineages and how temperature regulation may have evolved.