Warm-blooded

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In biology, a warm-blooded or homeothermic animal species is one whose members maintain thermal homeostasis; that is, they keep their body temperature at a roughly constant level, regardless of the ambient temperature. This involves the ability to cool down or produce more body heat. Warm-blooded animals mainly control their body temperature by regulating their metabolic rates, such as increasing their metabolic rate as the ambient temperature begins to decrease. This is characteristic of mammals and birds.

Both the terms "warm-blooded" and "cold-blooded" have fallen out of favour with scientists because of the vagueness of the terms and an increased understanding of the field. Body temperature types are not discrete categories. Each term may be replaced with one or more variants, see the next section for examples. Body temperature maintenance (thermoregulation) incorporates a wide range of different techniques that result in a body temperature continuum, with the traditional ideals of warm-blooded and cold-blooded being at opposite ends of the spectrum.

Contents

Definitions of warm-bloodedness

Warm-bloodedness generally refers to three separate aspects of thermoregulation.

  • Endothermy is the ability of some creatures to control their body temperatures through internal means such as muscle shivering or increasing their metabolism (Greek: endon = "within", thermē = "heat"). Some writers[who?] restrict the meaning of endothermy to mechanisms that directly raise the animal's metabolic rate in order to produce heat. The opposite of endothermy is ectothermy.
  • Homeothermy is thermoregulation that maintains a stable internal body temperature regardless of external influence. This temperature is often, though not necessarily, higher than the immediate environment (Greek: homoios = "similar", thermē = "heat"). The opposite is poikilothermy.
  • Tachymetabolism is the kind of thermoregulation used by creatures that maintain a high "resting" metabolism (Greek: tachys/tachus = "fast, swift", metabolēn = "throw beyond"). Tachymetabolic creatures are, essentially, "on" all the time. Though their resting metabolism is still many times slower than their active metabolism, the difference is often not as large as that seen in bradymetabolic creatures. Tachymetabolic creatures have greater difficulty dealing with a scarcity of food.

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