Endothermy and ectothermy are usually considered mutually exclusive characteristics. While endothermic animals (birds and mammals) can maintain internal body temperatures by producing metabolic heat, ectothermic animals depend on an external source of heat, thus their core temperature changes with that of their surroundings (Schmidt-Nielson, 1998). However, the temperate region bat proves an interesting exception in which these two classifications seem to converge. 
      During the warmer part of the year, when insect supplies are abundant, these bats maintain high well-regulated core temperatures, but when temperatures begin to drop along with the food supply they are faced with a choice—migration or hibernation (Wimsatt,  1970). Those that undergo the latter, allowing their body temperature to drop to nearly 0ºC for part of the year, can be referred to as temperal heterotherms. For these bats seasonal dormancy influences their entire life cycle, especially reproduction, growth, development, and fat storage—all which must take place during their period of activity (Davis, 1970; Lewis, 1993; Schmidt-Nielson, 1998; Wimsatt, 1970).

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