Rakali size and general features

An adult rakali swimming in the water

The rakali or Australian water-rat resembles a small otter in many ways. Its body is elongated and streamlined, and its tail is thick and muscular to help serve as a rudder when swimming. The hind feet are partly webbed and have a broad palm for efficient paddling.

A rakali has small ears, luxuriant whiskers and thick, lustrous fur.

The ears are small and can be folded flat against the head, and the muzzle is blunt and furnished with a luxuriant set of long whiskers. Both the eyes and nostrils are set high on the head so they remain well above the water while swimming. In contrast to a platypus (but like an otter), a rakali normally keeps its eyes open underwater to help locate and capture its prey (Woollard 1978). The fur is thick and lustrous, becoming water-repellent at the age of 2-3 months so animals dry quickly after exiting the water (Olsen 1980).

This rakali has a brown back and gold belly fur, along with its white tail tip.

Fur colour varies both regionally and sometimes within a given population, including black-backed animals with orange or dark grey bellies, brown-backed animals with gold or fawn-coloured bellies, and slate grey or mottled grey animals with cream-coloured bellies (Bettink 2016). Patches of white belly fur commonly occur in wild individuals that are otherwise pigmented (Gardner and Serena 1995).

Regardless of the overall colour pattern, virtually all rakali in the wild have a more or less conspicuous white tail tip, unless this has been lost through fighting or attempted predation (Olsen 1980; Watts and Aslin 1981; Bettink 2016).

Adult rakali measure up to 37 centimetres in length from their nose to rump, with a somewhat shorter tail. On aerage, adult males and females respectively weigh 0.8 kilograms (up to 1.3 kg) and 0.6 kilograms (up to 1.0 kg) (Van Dyck et al. 2013).

Photos courtesy of Ann Killeen (top), Lissa Ryan (middle) and James Pettit (bottom)

LITERATURE CITED

Bettink KA (2016) Shedding light on rakali: genetic and morphological differentiation in the Australo-Papuan goldenbellied water rat (Hydromys chrysogaster), with notes on the Barrow Island population. PhD Thesis, University of Western Australia, Nedlands.

Dawson TJ and Fanning FD (1981) Thermal and energetic problems of semiaquatic mammals: a study of the Australian water rat, including comparisons with the platypus. Physiological Zoology 54, 285-296.

Fanning FD and Dawson TJ (1980) Body temperature variability in the Australian water-rat, Hydromys chrysogaster, in air and water. Australian Journal of Zoology 28, 229-238.

Gardner JL and Serena M (1995) Observations on activity patterns, population and den characteristics of the water rat Hydromys chrysogaster along Badger Creek, Victoria. Australian Mammalogy 18, 71-75.

Olsen P (1980) Seasonal and maturational pelage changes, and injuries, in the eastern water rat, Hydromys chrysogaster, at Griffith, N.S.W. Australian Wildlife Research 7, 217-233.

Van Dyck S, Gynther I and Baker A (2013) Field Companion to The Mammals of Australia. New Holland Publishers: Sydney.

Watts CHS and Aslin HJ (1981) The Rodents of Australia. Angus & Robertson: Sydney.

 Woollard P, Vestjens WJM and MacLean L (1978) The ecology of the eastern water rat Hydromys chrysogaster at Griffith, N.S.W.: food and feeding habits. Australian Wildlife Research 5, 59-73.