Photo: Platypus - Nicole Duplaix

This article featured in Wildlife Lands Issue 14

The platypus (Ornithorhynchus anatinus) lays claim to having the highest level of evolutionary distinctiveness of any mammal species worldwide. Aside from echidnas, it is the only extant monotreme and its highly unusual features understandably perplexed early European naturalists. The platypus is a small, semi-aquatic species that uses its webbed feet to propel itself through rivers and its flat tail to store fat reserves. Males are slightly larger than females with an average length of 50cm and can weigh up to 2.4kg. Males also possess an ankle spur, which produces venom which can kill small animals and cause excruciating pain in humans.

The platypus’ bill is primarily a sensory organ equipped with touch-detecting mechanoreceptors and electrosensors that identify currents generated by muscular contractions. As platypus hunt with their eyes closed, their bill enables them to forage on river beds for invertebrate prey, particularly insect larvae.

Adults typically consume around a quarter of their body mass in live food each day, with lactating females reaching an astonishing 80-90%. This sees the species travelling up to 10km in feeding sessions that occupy approximately 12 hours a day. They rely on an intact and well-vegetated riparian zone for the provision of shade and shelter from predators and, during the day, typically shelter in a simple burrow at the water’s edge.

Females—sexually mature at around two years of age—dig longer (up to 30 metres) and more structurally complex burrows in which 1-3 eggs are laid in spring and incubated for just under 12 days prior to a lactation period of around four months. Milk is transferred from the mother's mammary glands to the skin where the young suckle her underbelly fur; platypuses do not have teats.

The eastern Australian river systems that platypus inhabit are often disrupted by dams, irrigation, flooding, drought and pollution caused by humans. Foraging mainly occurs nocturnally and, since it is primarily along the river bed, platypus are predisposed to getting tangled in plastic litter (particularly in more urban habitats) as well as being susceptible to drowning in submerged nets and fishing traps. Increased droughts, compounded by exposure to predation by dogs and risk of road mortality when moving over land are held as primary dangers.

The Action Plan for Australian Mammals classes the species as Near Threatened due to its overall population decline and threats directly affecting it and its habitat, including habitat degradation; water resource utilisation; fishing bycatch mortalities; and climate change. The Plan also notes that difficulties in reliably quantifying platypus numbers compromise estimations of population size and trends.

Despite only being listed as threatened in South Australia, it is faring particularly badly in Victoria. Studies show a complete absence of them in some river systems where they were formerly present. In other regions, rivers known to support thousands of platypuses at the time of European settlement have declined to less than 30 individuals, with juveniles completely absent.

Platypuses are found in several of our Wildlife Land Trust member sanctuaries, however long term river and watercourse maintenance requires the full support of the community and the government.  However, there is some positive news with the species recently being spotted in rivers in the northern Grampians for the first time in more than a decade.