Torpor differs from hibernation in that torpor is usually a short-term daily cycle. Many animals other than humans often induce hypothermia during hibernation or torpor. During hibernation, they experience periods of torpor and arousal. In the Australian autumn and winter, the echidna enters periods of torpor or deep hibernation. Examples include hibernating bears and torpor in bats. In hibernating species, males are known to mate with females in torpor. This happens in the spring shortly after waking up from winter torpor. Animals that hibernate are in a state of torpor, differing from sleep. The circulating hormone, corticosterone, is one signal that arouses a hummingbird from torpor. Marsupial torpor differs from non-marsupial mammalian (eutherian) torpor in the characteristics of arousal. They do not hibernate, but are capable of entering torpor. Huddling as an energy conserving mechanism is not as efficient as torpor. As winter progressed, the amount of time spent in torpor increases. There they enter a state of torpor, thus conserving energy. It alternates from slaughter to torpor to sex to torpor and back again to slaughter.