Water mouse (False water rat)
Common name: water mouse (previously known as the false water rat)
Scientific name: Xeromys myoides
Conservation status: The water mouse is listed as Vulnerable in Queensland (Nature Conservation Act 1992) and nationally (Environment Protection and Biodiversity Conservation Act 1999) and is ranked as a high priority for conservation under the Department of Environment and Heritage Protection Back on Track species prioritisation framework.
The water mouse is a small, native rodent that grows to approximately 10 cm in length. The species has a characteristic hunched body shape, small eyes, a broad snout and small rounded ears. The fur is very silky and water-resistant, and in juveniles it is a slate-grey colour above and pure white underneath. As animals age, the dorsal (back or top side) fur changes to a grey-brown colour and may be spotted with white flecks. The tail is sparsely haired and lacks the white-tip found in the more common water rat Hydromys chrysogaster. Juvenile water mice may be confused with house mice Mus musculus.
Habitat and distribution
The water mouse typically occurs in coastal saltmarsh, mangroves and adjacent freshwater wetland habitats in Australia and in coastal wetland areas of Papua New Guinea. In Australia, the species distribution encompasses coastal areas of central and south-east Queensland from Proserpine south to the Queensland/New South Wales border. The species is also known from the mainland and nearshore islands of the Northern Territory.
Life history and behaviour
The water mouse is a ground-dwelling, nocturnal rodent. Constructed nesting mounds and natural or artificial hollows located close to or above the high tide mark, are used for shelter during the day and between tidal cycles. Artificial structures may also be used for shelter when no other suitable sites exist.
Little is known of the reproductive biology of this species, although it is thought to breed throughout the year. Studies suggest that animals of mixed age and gender may share a nesting mound, although only one sexually active male is usually present. The nest may also be used over a number of years by successive generations.
The water mouse utilises exposed mangrove substrates and intertidal saltmarsh habitats for foraging, following the outgoing tide and foraging until advancing water covers these habitats. The species diet consists of a number of invertebrates including several crab species, small mud lobsters, marine shellfish and snails. They deposit the remains of their meal in small middens. The estimated home range used for foraging is 0.8 ha for males and 0.6 ha for females.
In the past 30 years, local population reductions and disappearances have been recorded in Queensland and the Northern Territory. The water mouse is mostly threatened by habitat loss, fragmentation and degradation. This has resulted from urban development, sand mining, land reclamation, swamp drainage, feral animals, recreational vehicles, discharge of polluted waters and chemical pollution (runoff from agricultural and urban lands, exposure of acid sulphate soils and off-shore pollution events). These degrading processes reduce potential feeding resources and nesting opportunities, promote weed invasion and increase predation by feral animals (foxes, pigs and cats).
- Negotiate voluntary conservation agreements between landowners and the State to protect water mouse populations and habitat on private land.
- Identify habitat supporting water mouse populations, map the species distribution and maintain updated distributional records to facilitate protection of populations.
- Maintain suitable habitat for this species by managing key threatening processes.
- Increase knowledge of the species biology and ecology through research studies, ecological assessments and field monitoring programs.
- Promote population expansion by rehabilitating habitat adjacent to existing populations.
- Implement community awareness programs to increase public awareness of the threats impacting on this species and its habitat.
What can you do to help this species?
- Become involved in voluntary conservation agreement schemes such as the Nature Refuge program, to protect water mouse habitat on your land.
- Control domestic animals (dogs and cats) to reduce predation pressure on water mouse populations in urban areas.
- Avoid or minimise land-use activities on land adjacent to water mouse habitat that may affect non-target species (e.g. use of herbicides and pesticides).
- Avoid landscape modifications that disturb water mouse habitat (e.g. excavation, construction, installation of flow control gates, discharge of polluted waters).
- Manage livestock to prevent habitat degradation from grazing and trampling in saltmarsh and mangrove areas.
Department of the Environment and Resource Management. 2010. National recovery plan for the water mouse (false water rat) Xeromys myoides.Report to Department of the Environment, Water, Heritage and the Arts, Canberra. Department of the Environment and Resource Management, Brisbane.
Department of Sustainability, Environment, Water, Population and Communities. 2011. Xeromys myoides water mouse, false water rat in Species Profile and Threats Database, Department of Sustainability, Environment, Water, Population and Communities, Canberra.
Environment Australia. 1995. The Action Plan for Australian Rodents. Department of Sustainability, Environment, Water, Population and Communities, Canberra.
Redhead, TD. 1983. False Water-rat Xeromys myoides, p. 369 in The Australian Museum Complete Book of Australian Mammals. Angus and Robertson, Sydney.
Watts, CHS and Aslin, HJ. 1981. The Rodents of Australia. Angus and Robertson, Sydney.