Mammals endotherms

Birds and mammals are endothermic vertebrates. Not coincidentally, they are the only vertebrates with unique external body coverings—feathers and hair, respectively. For both groups, these body coverings evolved as an adaptation to reduce heat loss. A bird s feathers were originally adaptive because they helped keep the animal warm, not because they helped it to fly. 

Mammals and birds are the only groups of animals having a capacity for effective systemic endothermic homeothermy. The origin of this important capacity has long intrigued physiol-... 

The differences in metabolic rate between ectotherms and endotherms thus are due to the preexponential term a, which is approximately four- to fivefold higher in birds and mammals relative to reptiles. On a mass-specific basis (for instance, oxygen consumption per gram wet mass) the mass exponent is near... 

Animals that are described as warm blooded, or endothermic, maintain a constant internal temperature, even when exposed to extreme temperatures in their environment. In mammals, this internal temperature is about 97°F (36°Q, while in birds, it is warmer, around 108°F (42°Q. 

Sometimes there is confusion due to different use of terms. Thermodynamics calls a process exothermic when heat is given off by the system and endothermic when it consumes heat. In biology, warm-blooded (homeothermic) animals like mammals and birds that produce heat to keep their body temperature constant are called endotherms and their behaviour endothermic, in contrast to the thermodynamical direction. Their counterparts with changing body temperatures are ecto-therms (not exotherms) or cold-blooded poikilothermic) animals. Nevertheless, all of them produce heat as a by-product of their metabolism so that they can be monitored by (exothermic) calorimetry. 

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