By Geoff Williams, Australian Platypus Conservancy
The platypus is widely recognised as a uniquely Australian animal. By comparison, relatively few people know that the Australian water-rat (Hydromys chrysogaster) is a genuine native rodent that was a natural part of our environment long before its pest cousins – the black rat and brown rat – arrived with the early colonists. The water-rat (also known as rakali) is an extremely attractive mammal. Its thick coat of soft fur, dense whiskers, blunt muzzle, partly webbed hind feet, and furry tail, all help create a resemblance to a miniature otter.
Both platypuses and water-rats are top predators in freshwater systems, eating insects, yabbies and mussels. However, the size of prey that can be consumed by a platypus is limited by the fact that its bill is equipped only with grinding pads. In contrast, a water-rat has formidable teeth which can be used to kill and eat fish, frogs and water birds.
Both species are mainly nocturnal but can sometimes be seen in the day. Of the two, water-rats are probably more active during daylight hours, especially in winter. Unlike platypus, water-rats often leave the water to eat (sitting up and holding food in their forepaws) or run along the bank searching for food. A feeding “table” – a pile of food fragments, such as yabbie claws or mussel shells, on a rock or log – often gives a clue to the presence of the species. Although similar in terms of size and colour, the two aquatic mammals can be distinguished by careful observation: the white tip to the water-rat’s tail being the best identifying feature.
Officially classified as “Common”, there is considerable evidence that numbers of both water-rats and platypus have declined, especially in urban and agricultural landscapes. The Australian Platypus Conservancy research program along the Murray, supported by Norske Skog, has found water-rats throughout the Albury section of the river but at a much lower density than platypus.
Both species are difficult to study in the wild and their exact status and distribution remains uncertain. Consequently, reports of sightings of both platypus and water-rats are of great value. Details of when and where animals have been seen (including in the past) can be sent to the Australian Platypus Conservancy website (www.platypus.asn.au).
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