<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Hibernation is a mechanism used by many mammals to reduce energy expenditure and survive food shortage over the winter . Hibernation may be predictive or consequential . An animal prepares for hibernation by building up a thick layer of body fat during late summer and autumn that will provide it with energy during the dormant period . During hibernation, the animal undergoes many physiological changes, including decreased heart rate (by as much as 95%) and decreased body temperature . In addition to shivering, some hibernating animals also produce body heat by non-shivering thermogenesis to avoid freezing . Non-shivering thermogenesis is a regulated process in which the proton gradient generated by electron transport in mitochondria is used to produce heat instead of ATP in brown adipose tissue . Animals that hibernate include bats, ground squirrels and other rodents, mouse lemurs, the European hedgehog and other insectivores, monotremes and marsupials . Although hibernation is almost exclusively seen in mammals, some birds, such as the common poorwill, may hibernate . </P> <P> Diapause is a predictive strategy that is predetermined by an animal's genotype . Diapause is common in insects, allowing them to suspend development between autumn and spring, and in mammals such as the roe deer (Capreolus capreolus, the only ungulate with embryonic diapause), where a delay in attachment of the embryo to the uterine lining ensures that offspring are born in spring, when conditions are most favorable . </P> <P> Aestivation, also spelled estivation, is an example of consequential dormancy in response to very hot or dry conditions . It is common in invertebrates such as the garden snail and worm but also occurs in other animals such as the lungfish, salamanders, desert tortoises, and crocodiles . </P>

Insects undergo a period of dormancy in winter or summer called