Hydromys chrysogastergolden-bellied water rat
Geographic Range
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)
- Biogeographic Regions
- australian
Habitat
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)
- Habitat Regions
- tropical
- saltwater or marine
- freshwater
- Aquatic Biomes
- lakes and ponds
- rivers and streams
- coastal
- Other Habitat Features
- urban
- suburban
- agricultural
- riparian
- estuarine
Physical Description
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)
- Other Physical Features
- endothermic
- bilateral symmetry
Reproduction
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)
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- viviparous
-
- Breeding season
- Breeding occurs during spring and summer.
-
- Range number of offspring
- 8 to 15
-
- Average number of offspring
- 3.8
- AnAge
-
- Average gestation period
- 35 days
-
- Average gestation period
- 36 days
- AnAge
-
- Average weaning age
- 35 days
-
- Average age at sexual or reproductive maturity (female)
- 1 years
-
- Average age at sexual or reproductive maturity (female)
Sex: female - 163 days
- AnAge
- Average age at sexual or reproductive maturity (female)
-
- Average age at sexual or reproductive maturity (male)
- 1 years
-
- Average age at sexual or reproductive maturity (male)
Sex: male - 135 days
- AnAge
- Average age at sexual or reproductive maturity (male)
Young are born helpless and are cared for by their mother in her nest burrow until they are weaned, at about 35 days old.
- Parental Investment
- altricial
- female parental care
Lifespan/Longevity
Longevity in water rats is unknown.
-
- Average lifespan
Status: captivity - 7.3 years
- AnAge
- Average lifespan
Behavior
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)
Communication and Perception
Food Habits
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)
- Primary Diet
-
carnivore
- piscivore
- eats non-insect arthropods
- molluscivore
- Animal Foods
- birds
- mammals
- amphibians
- reptiles
- fish
- eggs
- insects
- terrestrial non-insect arthropods
- mollusks
- aquatic crustaceans
- Foraging Behavior
- stores or caches food
Predation
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)
-
- Known Predators
-
- eagles (Accipitridae)
- buzzards (Accipitridae)
- kites (Accipitridae)
- snakes (Serpentes)
Ecosystem Roles
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.
Economic Importance for Humans: Positive
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)
Economic Importance for Humans: Negative
Active burrowers, H. chrysogaster individuals have damaged channel banks and water-control structures. (Watts and Aslin, 1981)
Conservation Status
Water rats are widespread and abundant, they are not threatened.
-
- IUCN Red List
-
Least Concern
More information
-
- IUCN Red List
-
Least Concern
More information
-
- US Migratory Bird Act
- No special status
-
- US Federal List
- No special status
-
- CITES
- No special status
Contributors
Barbara Lundrigan (author), Michigan State University, Kim Pfotenhauer (author), Michigan State University.
Glossary
- Australian
-
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
- agricultural
-
living in landscapes dominated by human agriculture.
- altricial
-
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
- bilateral symmetry
-
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- bog
-
a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.
- carnivore
-
an animal that mainly eats meat
- chemical
-
uses smells or other chemicals to communicate
- coastal
-
the nearshore aquatic habitats near a coast, or shoreline.
- endothermic
-
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
- estuarine
-
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
- female parental care
-
parental care is carried out by females
- fertilization
-
union of egg and spermatozoan
- freshwater
-
mainly lives in water that is not salty.
- internal fertilization
-
fertilization takes place within the female's body
- iteroparous
-
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
- marsh
-
marshes are wetland areas often dominated by grasses and reeds.
- molluscivore
-
eats mollusks, members of Phylum Mollusca
- motile
-
having the capacity to move from one place to another.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- piscivore
-
an animal that mainly eats fish
- riparian
-
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
- saltwater or marine
-
mainly lives in oceans, seas, or other bodies of salt water.
- seasonal breeding
-
breeding is confined to a particular season
- sedentary
-
remains in the same area
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- solitary
-
lives alone
- stores or caches food
-
places a food item in a special place to be eaten later. Also called "hoarding"
- suburban
-
living in residential areas on the outskirts of large cities or towns.
- swamp
-
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
- tactile
-
uses touch to communicate
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- urban
-
living in cities and large towns, landscapes dominated by human structures and activity.
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
References
Fanning, F., T. Dawson. 1980. Body temperature variability in the Australian water rat, *Hydromys chrysogaster*, in air and water. Australian Journal of Zoology, 28: 229-238.
Watts, C., H. Aslin. 1981. The rodents of Australia. Sydney: Angus & Robertson Publishers.