minimized. The echidna is endothermic, and can maintain body temperatures of around 32 °C. It can also reduce its metabolism and heart rate and body temperature. In addition to brief and light bouts of torpor throughout the year, the echidna enters periods during the Australian winter when it hibernates, both in cold regions and in regions with more temperate climates. During hibernation, the body temperature drops to as low as 4 °C (39 °F). The heart rate falls to four to seven beats per minute—down from 50 to 68 at rest—and the echidna can breathe as infrequently as once every three minutes, 80 to 90% slower than when it is active. Metabolism can drop to one-eighth of the normal rate. Echidnas begin to prepare for hibernation between February and April, when they reduce their consumption and enter brief periods of torpor. Males begin hibernating first, while females that have reproduced start later. During periods of hibernation, the animals average 13 separate bouts of torpor, which are broken up by periods of arousal lasting 1.2 days on average. These interruptions tend to coincide with warmer periods. Males end their hibernation period in mid-June, while reproductive females return to full activity in July and August; nonreproductive females and immature echidnas may not end hibernation until two months later. During euthermia, the body temperature can vary by 4 °C per day. The metabolic rate is around 30% of that of placental mammals, making it the lowest energy-consuming mammal. This figure is similar to that of other animals that eat ants and termites; burrowing animals also tend to have low metabolism generally. Echidnas hibernate even though it is seemingly unnecessary for survival; they begin their hibernation period while the weather is still warm, and food is generally always plentiful. One explanation is that echidnas maximize their foraging productivity by exercising caution with their energy reserves. Another hypothesis is that they are descended from ectothermic ancestors, but have taken to periodic endothermy for reproductive reasons, so that the young can develop more quickly. Supporters of this theory argue that males hibernate earlier than females because they finish their contribution to reproduction first, and they awake earlier to undergo spermatogenesis in preparation for mating, while females and young lag in their annual cycle. During the hibernation period, the animals stay in entirely covered shelter. Short-beaked echidnas can live anywhere with a good supply of food, and