The periodicity of the sleep cycle is strongly correlated with body size both between and within species. This may be related to the demands of thermoregulation. During quiet sleep the thermoregulatory mechanisms work normally but there is no response to thermal stress during active sleep. This could have serious implications for small animals (see gigantothermy) whose body temperature is more easily influenced by ambient temperature because of their lesser thermal capacity. So, as a rule, smaller animals have shorter periods of active sleep, ending before becoming thermally threatening.
- ↑ McFarland, D., (2006) Oxford Dictionary of Animal Behavior. Oxford:OUP