Most sleep for a mammal

The most sleep recorded for a mammal based on average daily sleep period is 19.9 hours, as recorded in 1969 for a specimen of the little brown bat Myosotis lucifugus, a small, very abundant species of mouse-eared bat native to much of North America, especially southern Canada and the northern continental states of the USA. However, some researchers have questioned this result, speculating that as the bat specimen in question had been hooked up to a computer rather than roosting normally by hanging upside-down from a cave roof, and also because the external temperature had been altered, this may not count as natural conditions.

Assuming that such a lengthy period of sleep per 24-hour period is natural, however, it has been suggested that the reason for it is for the bat to conserve as much energy as possible, by only hunting during the few hours in each such period when its insect prey is most available and hence most readily caught.

Also, it is believed that mammals like bats that sleep in hidden, concealed places where predators are unlikely to reach them are not on constant alert from such threats, and therefore are able to sleep longer and deeper than mammals that are exposed to such threats and which therefore need to stay alert as much as possible.