Although energy conservation by cold-climate adult endotherms in winter is often viewed as the main function of torpor, recent evidence suggests that this may not always be the case. We examined whether other functions of torpor may be equally or even more important in some instances. Torpor enhances fat storage during migration, apparently permits prolonged female sperm storage in bats, allows reproduction with limited or fluctuating food supply, and delays parturition until more favorable

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... ods. Torpor appears to increase the efficiency of energy and nutrient use during development. Further, torpor reduces water requirements, appears to permit persistence during droughts, reduces the load of some parasites, permits co-existence of competing species, and also reduces the risk of predation and mammalian extinctions. Thus, the functions of torpor are complex and some of these appear to be not just proximate.