Rakali mainly feed in the water, with their staple diet in freshwater habitats comprising fish, aquatic insects, crayfish, mussels, clams and (to a much lesser extent) frogs and turtles. Small amounts of particularly nutritious aquatic plants may also be eaten. They will also dine opportunistically on waterbirds, including coots, grebes, ducks and swamp hens Porphyrio porphyrio (Woollard et al. 1978). Predation by rakali on young shearwaters Puffinus tenuirostrus (McNally 1960) or penguin chicks (Preston 2008) has also been documented. Introduced fish (including goldfish Carassius auratus, redfin perch Perca fluviatilis and mosquito fish Gambusia affinis) were apparently consumed in preference to native fish at a study site in New South Wales, suggesting that rakali may help to control pest fish species (Woollard et al. 1978).
Unlike the platypus, rakali often forage on the banks and will sometimes travel even farther from the water to find food, with house mice eaten during a mouse plague (Woollard et al. 1978). Many anecdotal accounts attest to this animal’s appetite for foods of human origin, such as picnic leftovers or pet food left on a porch. Particularly high numbers of rakali may occur near sites where fishermen routinely clean their catch (Smales 1984).
Rakali also routinely kill the introduced cane toads found in Australia’s tropical north. By first flipping the toads over, they avoid biting into the poisonous parotid glands found in the toad’s neck region (see photo above).
Rakali will normally carry food items to a convenient dining spot on a log, rock, reed clump or handy branch elevated above the water (as shown at right) before consuming them. Dining platforms can be located either near the water’s edge or in the channel. Large piles of clam shells, crayfish claws and fish bones and scales often accumulate at such spots (McNally 1960), representing the remains of many meals and providing strong evidence that a rakali population is active in the vicinity.
Photos courtesy of Carolyn Hall (top, bottom) and Louis Delamoir (middle)
LITERATURE CITED
McNally J (1960) The biology of the water rat Hydromys chrysogaster Geoffroy (Muridae: Hydromyinae) in Victoria. Australian Journal of Zoology 8, 170-180.
Preston T (2008) Water rats as predators of Little Penguins. The Victorian Naturalist 125, 165-168.