During hibernation there is a slowing of all metabolic processes, and thus it is normally considered to be incompatible with reproduction. In Tasmania the egg-laying mammal, the echidna Tachyglossus aculeatus hibernates for several months before mating in mid-winter, and in previous studies we observed males with females that were still hibernating. We monitored the reproductive activity of radio-tracked echidnas by swabbing the reproductive tract for sperm while external temperature loggers provided information on the timing of hibernation. Additional information was provided by camera traps and ultrasound imaging. More than a third of the females found in mating groups were torpid, and the majority of these had mated. Some females re-entered deep torpor for extended periods after mating.

The four extant species of echidnas and the platypus are the only living mammals that lay eggs and the only surviving members of the order Monotremata. Echidnas live in Australia and New Guinea. The echidnas are named after Echidna , a creature from Greek mythology who was half-woman, half-snake, as the animal was perceived to have qualities of both mammals and reptiles. Echidnas are medium-sized, solitary mammals covered with coarse hair and spines. Superficially, they resemble the anteaters of South America and other spiny mammals such as hedgehogs and porcupines. They are usually black or brown in colour.

Sex-determining systems have evolved independently in vertebrates. Placental mammals and marsupials have an XY system, birds have a ZW system. Reptiles and amphibians have different systems, including temperature-dependent sex determination, and XY and ZW systems that differ in origin from birds and placental mammals.

All rights reserved. Gemma Morrow and Stewart Nicol from the University of Tasmania have spent the last decade studying the short-beaked echidnas of Tasmania. Over that time, they discovered many instances of males mating with torpid females in deep hibernation, or with females who roused themselves briefly only to re-enter their deep slumber. Over the last two years, the voyeuristic duo use a combination of cameras, radio-trackers and infrared motion detectors to get a more intimate glimpse at the bizarre sex life of these animals.