Final answer:
Heterotherms are animals that generate body heat both metabolically and from the environment at different times, exhibiting a blend of characteristics from both endotherms and ectotherms.
Step-by-step explanation:
Animals that generate body heat metabolically at some times and from the environment at other times are referred to as heterotherms. These animals exhibit characteristics between the endotherms, which maintain a fairly constant body temperature through metabolic means, and ectotherms, which rely on external environmental conditions to regulate their body temperature.
Unlike endotherms that have a stable body temperature and can maintain high metabolic rates and activity levels in cold environments, heterotherms can switch between endothermy and ectothermy to conserve energy. For instance, bats or hummingbirds may go into a torpid state during cold nights to save energy, allowing their body temperature to fall and rise with the environment.
Heterotherms have the advantage of adjusting their body temperature according to the need, either to save energy by relying on environmental warmth or to increase metabolic heat production for higher activity levels.