Endotermne

Endotermne are animals that regulate their body temperature largely through internal metabolic heat production rather than relying primarily on environmental temperatures. They typically maintain a relatively constant internal temperature, though some species show seasonal or daily fluctuations or enter states of reduced metabolic activity.

In the traditional sense, endothermy is most clearly associated with birds and mammals, which sustain higher and more stable body temperatures. Some other groups display regional or partial endothermy, producing heat in specific tissues or during particular activities. For example, certain fish such as lamnid sharks and tunas generate heat in deep muscles and surrounding tissues to support sustained swimming and sensory function. Among invertebrates, localized heat production has been observed in some cephalopods, but these do not constitute full endothermy.

Physiological mechanisms of endothermy include sustained metabolic heat production and insulating features such as fur, feathers, and fat. Thermoregulation is coordinated by the hypothalamus and involves behavioral and physiological responses. Birds and mammals often use additional strategies such as non-shivering thermogenesis in brown adipose tissue (especially in infant mammals), vasomotor regulation, and, when needed, shivering or panting to modulate heat exchange. Countercurrent heat exchange in limbs helps minimize heat loss in extremities.

Endothermy imposes high energy demands, supporting high activity levels and broader geographic ranges, but requiring abundant and consistent food intake. It has evolved independently in several lineages, notably birds and mammals, and is accompanied by diverse adaptations and occasional heterothermy, torpor, or hibernation in response to environmental conditions.