Hydromys chrysogaster
golden-bellied water rat

Hydromys chrysogaster dwells in freshwater lakes and rivers throughout Australia and Tasmania and on offshore islands. They are also found on New Guinea. (Watts and Aslin, 1981)

Hydromys chrysogaster individuals live mainly near permanent fresh water. They live on land but depend on the water for food. Also present along the coastline, H. chrysogaster do not need completely fresh water. They can also survive in areas where rivers and streams have become polluted or are brackish. (Watts and Aslin, 1981)

About the size of a rabbit, H. chrysogaster is well adapted for water. The toes are webbed on front and hind feet, which are broad and act as paddles. Hydromys chrysogaster has numerous whiskers at the end of a long, blunt muzzle. The head is flat with small ears and eyes. The most notable characteristic is the water rat’s thick white tipped tail. Hydromys chrysogaster varies in color from a brown black to gray, making them somewhat cryptic in their surroundings. Some are uniform in color, while others have lighter undersides. The one unifying feature is the white tipped tail. (Watts and Aslin, 1981)

Little is known of the mating system of water rats.

Water rats breed in the spring and summer. Females have an estrous cycle of approximately eleven days. The gestation period is about 35 days. Females can enter estrus immediately after giving birth, so litters can be produced only 35 days apart. Usually, water rats have litters of four to five young. During a good breeding season, females can have two or three litters.

At birth, the young are blind. They are usually lighter in color than the adults, but already have the characteristic white tipped tail and partially webbed feet. The young grow quickly and are usually independent after about 35 days. However, after this initial growth, maturity to adulthood takes longer. Breeding does not occur until the young are at least one year old and full size is attained at about two years of age. (Watts and Aslin, 1981)

Young are born helpless and are cared for by their mother in her nest burrow until they are weaned, at about 35 days old.

Longevity in water rats is unknown.

Hydromys chrysogaster live in burrows alone or with young. However, populations are concentrated in certain areas. Their burrows run parallel to the banks of lakes or rivers. The entrances are often hidden under a log or root. Inner nest chambers are about 20 cm high. These burrows may have more than one chamber and a second entrance. Water rats got their name from their ability to swim and dive. They are often mistaken for a platypus (Watts and Aslin, 1981). However, H. chrysogaster individuals are not as well equipped as platypus are for aquatic life. They do not have water resistant fur or many adaptations for the water. This becomes a problem when the temperature is low. Water rats will go into rivers for short periods of time in the winter, but they still suffer regional hypothermia from both the air and water when the temperature drops. One adaptation that may help them survive this hypothermia is an interscapular pad of brown fat. Metabolism of this pad insulates the heart and allows warm blood to flow to the heart and the spinal cord during cold weather. (Fanning and Dawson, 1980)

Hydromys chrysogaster feeds mainly on crustaceans, mollusks, and fish, although they have been observed feeding on aquatic insects, frogs, house mice, the eggs and young of waterfowl, poultry, and turtles, and even attacking bats. Hydromys chrysogaster have also been observed eating cane toads, an introduced species that is toxic to many other predators. They often have a favorite feeding platform on which they collect piles of food before eating it. Hoarding food in the nest site is also common. Mussels are opened by their strong incisors. (Fanning and Dawson, 1980; Watts and Aslin, 1981)

Eagles, buzzards and kites prey on water rats, as well as snakes and small mammalian carnivores. Water rats mainly escape predation by escaping to burrows or into the water. (Watts and Aslin, 1981)

Water rats are abundant and are an important prey base for many small to medium-sized predators. Their burrowing and foraging activities probably also help in the redistribution of nutrients in systems.

Hydromys chrysogaster are able to withstand pollution in cities and even thrive there. They are often observed by humans because they are sometimes active during the day. Farmers benefit from H. chrysogaster because they often destroy yabbies, other small rodents, which destroy irrigation systems. By eating pond snails, water rats also protect livestock from the parasites that are transmitted through snails. (Watts and Aslin, 1981)

Active burrowers, H. chrysogaster individuals have damaged channel banks and water-control structures. (Watts and Aslin, 1981)

Water rats are widespread and abundant, they are not threatened.