Torpor in the Echidna, Tachyglossus aculeatus

Echidnas maintained at 5°C without food became torpid after varying lengths of time, with minimum values of body temperature (TE) 5.5°C, heart rate seven beats per minute, and oxygen consumption 0.03 ml 02 per gm body wt per hour. Initially the torpid animals were able to arouse at ambient temperature (TA) 5°C, requiring about 20 hr to return TB to within the normal awake range of 26 to 29 °C. However, arousal from repeated periods of torpor generally required an increase in TA. Similar torpor was observed in one echidna maintained at 10°C without food in the laboratory and in another burrowed in the field at ground temperature 9°C. In both TB fell to within 0.5°C of TA. Under these conditions repeated spontaneous arousals are possible. On the basis of these physiological data the echidna appears to be a true mammalian hibernator.