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Warm-blooded animals maintain thermal homeostasis; that is, they keep their core body temperature at a nearly constant level regardless of the temperature of the surrounding environment. This can involve not only the ability to generate heat, but also the ability to cool down. Warm-blooded animals control their body temperature by regulating their metabolic rates (e.g. increasing their metabolic rate as the surrounding temperature begins to decrease). Both the terms "warm-blooded" and "cold-blooded" have fallen out of favor with scientists, because of the generality of the terms, and due to an increased understanding in this field. Body temperature types do not fall into simple either/or categories. Each term may be replaced with one or more variants (see: breaking down warm-bloodedness). Body temperature maintenance 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.
Breaking down warm-bloodedness Warm-bloodedness generally refers to three separate aspects of thermoregulation. A large proportion of the creatures traditionally called "warm-blooded" (mammals and birds) fit all three of these categories. However, over the past 30 years, studies in the field of animal thermophysiology have revealed many species belonging to these two groups that don't fit all these criteria. For example, many bats and small birds are poikilothermic and bradymetabolic when they sleep for the night, or day. For these creatures, another term was coined: heterothermy. Further studies on animals that were traditionally assumed to be cold-blooded have shown that most creatures incorporate different variations of the three terms defined above, along with their counterparts (ectothermy, poikilothermy and bradymetabolism), thus creating a broad spectrum of body temperature types (see between warm-blooded and cold-blooded). Mechanisms Endotherms include birds and mammals. The advantages of endothermy are increased enzyme activity and a constant body temperature, allowing these animals to be active in cold temperatures. A prime disadvantage is the need to maintain thermoregulation, even during inactivity, otherwise the organism will die. (Cold-blooded animals, such as fish and reptiles, are called ectotherms, meaning that they cannot control their internal temperature.) In winter, there may not be enough food to enable an endotherm to keep its metabolic rate stable all day, so some organisms go into a controlled state of hypothermia called hibernation, or torpor. This deliberately lowers the body temperature to conserve energy. In hot weather, endotherms expend considerable energy to avoid overheating: they may pant, sweat, lick, or seek shelter or water. Diverse mechanisms regulate body temperature, such as shivering (when muscles contract, their cells respire more - respiration releases heat and is incidentally the main heat source in the body), blanching (circulatory changes to direct less heat to the skin), flushing (circulatory changes to radiate more heat from the skin), panting, or sweating (to increase heat loss through evaporation). Warm-blooded versus cold-blooded
Between warm-blooded and cold-blooded Scientific understanding of the multitude of thermal regulation regimes existing in the natural world has advanced greatly since the original distinction was made between warm- and cold-blooded animals, and the issue has been studied much more extensively. For example, we now know that cold-blooded animals all use behavioral means to adjust their internal temperatures, often very effectively. There are also creatures that do not properly fall into either category. Some examples of in-between creatures include: See also | ||||||||||
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