Behaviour and ecology of monotremes

The extant monotremes share a number of general features that must reflect their common ancestor and constrain their ecology and behaviour. All of the extant monotremes have diets which consist principally of invertebrates: platypuses feed mainly on benthic macroinvertebrates, long-beaked echidnas feed on invertebrates in the soil, leaf litter and decaying logs, while short-beaked echidnas, although principally feeding on ants and termites, also eat a range of other soil invertebrates. Platypuses and long-beaked echidnas are predominantly nocturnal, and although the shortbeaked echidnas are often seen during the day, the majority of their activity also occurs during the night. The long-beaked echidnas, apart from a possible recent population in the Kimberley region in north-west Australia, are restricted to New Guinea, and platypuses occur in freshwater environments in eastern Australia, but short-beaked echidnas occur throughout Australia, and in New Guinea.

Monotremes are solitary and females have well established home ranges, while males have larger home ranges and compete for matings. All of the monotremes have very large testes, indicating strong competition between males, and adult males have a crural or femoral gland connected by a duct to a spur on the ankle. The glands increase in size during the breeding season and are clearly important in breeding behavior. The platypus and short-beaked echidnas are seasonal breeders but the data for longbeaked echidnas are equivocal. Gestation is very short compared with lactation, and late in the gestation period a pregnant female echidna will enter a nursery burrow to lay her single egg, while the female platypus lays two eggs in her nest or burrow. The eggs are incubated in the female’s pouch and hatch after 10 – 11 days. The lactation period for platypuses is about 19 weeks, but for echidnas there are large differences between populations from different parts of Australia: in eastern Australian echidnas the lactation period may be as little as 20 weeks, and in Western Australian and Kangaroo Island as much as 30 weeks. There are also differences in other aspects of maternal care between these echidna populations.

All the monotremes have low metabolic rates, but echidna metabolic rates are extremely low, and short-beaked echidnas in cooler areas show long periods of hibernation. This low energy way of life makes the possession of a large, energetically expensive brain hard to explain, and it is possible that their behaviour, particularly their social behaviour, is more complex than previously thought.