WATER RAT

any of a number of rodents normally found in or near water. The term is often used collectively for about eight genera of Australian and Oriental rodents forming the subfamily Hydromyinae of the family Muridae (order Rodentia). It is also used for the muskrat (q.v.) and the water vole (see vole). Among the hydromyine water rats are the Australian-New Guinean water rats, or beaver rats (Hydromys), three species of large, primarily carnivorous rodents found along streams, swamps, estuaries, and other aquatic habitats. From 20 to 35 cm (8 to 14 inches) long without the long tail, they have partly webbed hind feet and dense, seallike, gray or golden- to dark-brown fur. Their nostrils can be closed off, an adaptation to their semiaquatic life. They rest by day in burrows, hollow logs, or other cover and emerge in the evening to hunt for prey, such as mussels, snails, fishes, crabs, frogs, and crayfish; they also eat birds' eggs and plant matter. They breed in late winter or spring, the female bearing a litter of usually four or five young, which become fully adult before they are a year old. Monckton's water rat (Crossomys moncktoni) is still better adapted to its environment; it has involuted external ears and a characteristic hairy tail with a bristly underseam that allows it rudderlike control of its movements in water. Other genera of the subfamily include Chrotomys, Paraleptomys, and Pseudohydromys.