Endotherm

An endotherm maintains body temperature largely by producing heat through internal metabolic processes. Birds and mammals are the principal living groups with this trait.

Non-shivering thermogenesis: Heat production without muscle contractions, often driven by specialized adipose tissue. Brown adipose tissue can raise heat output without shivering.
Thermoregulation: The control of body temperature through physiological and behavioral processes. Endothermy is one strategy within the broader problem of temperature control.
Thermal neutral zone: The range of ambient temperatures in which an endotherm maintains body temperature without increasing metabolic heat production. Within this range, thermoregulation requires less extra energy.
Synapsid: A member of the vertebrate lineage that includes mammals and their extinct relatives. Mammalian endothermy arose within the synapsid lineage.
Shivering: Rapid, involuntary muscle contractions that generate heat. Endotherms recruit shivering when other heat sources cannot meet cold exposure.
Ectotherm: An organism whose body temperature depends mainly on heat exchanged with its environment. Ectotherms rely more on environmental heat than endotherms do.
Basal metabolic rate: The rate of energy expenditure by an awake, resting organism under standardized conditions. Its measurement helps compare the baseline energetic demands of endotherms.
Mammalia: The vertebrate class containing mammals, distinguished by traits including hair and milk production. Living mammals are one of the two major endothermic vertebrate groups.
Vasoconstriction: Narrowing of blood vessels that reduces blood flow through a tissue. Constriction near the skin limits heat loss to cold surroundings.
Homeothermy: The maintenance of a relatively stable body temperature over time. Endothermy often supports stable temperature, but the two properties are not identical.

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