Water mouse (False water-rat)

Common name: water mouse (previously known as the false water rat)

Scientific name: Xeromys myoides

Family: Muridae

Conservation status: The water mouse is listed as Vulnerable in Queensland (Nature Conservation Act 1992) and nationally (Environment Protection and Biodiversity Conservation Act 1999).

Description

The water mouse is a small, native rodent with a combined head and body length of around 12 cm and a tail length of about 10 cm. The species has small eyes, a broad snout and small rounded ears. The fur is very silky and water-resistant. In juveniles, it is a slate-grey colour above and pure white underneath, but as animals age, the dorsal (back or top side) fur changes to a grey-brown colour and may develop indistinct white flecking. The tail is sparsely haired and lacks the white tip found in the more common and much larger water rat Hydromys chrysogaster. Juvenile water mice may be confused with the introduced house mice Mus musculus.

Habitat and distribution

The water mouse typically occurs in coastal saltmarsh, mangroves and adjacent freshwater wetland habitats in eastern and northern Australia. It has also been recorded in association with melaleuca wetlands near the Bensbach River of Papua New Guinea. In Australia, the distribution of this species encompasses coastal areas of mid-east and south-east Queensland, from Proserpine, south to near the border between Queensland and New South Wales. In the Northern Territory, it is also known from the mainland and Melville Island.

Life history and behaviour

The water mouse is mainly terrestrial and nocturnal. Where it occupies tidal habitats, constructed nest 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. Given the size of the occupants, mud nest mounds may be surprisingly large, standing up to 60 cm above the surrounding substrate. 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 mound may be used and maintained 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 until advancing water forces a retreat to shelter. Its diet consists of various invertebrates, including several crab species, small mud lobsters, marine bivalves and snails and a marine polyclad flatworm. Inedible remains of meals, such as crab carapaces, may be deposited in small middens. Estimated home ranges are 0.8 ha for males and 0.6 ha for females.

Threatening processes

Over the past 30 years, local population reductions and disappearances have been recorded in Queensland and the Northern Territory. The water mouse is primarily threatened by the loss, fragmentation and degradation of habitat. This has resulted from urban development, sand mining, land reclamation, swamp drainage, trampling of substrate and grazing by cattle, damage from 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 such as oil spills). Compounding these impacts are the predation pressures exerted by feral animals, most importantly red foxes and pigs. Habitat fragmentation and degradation reduce potential feeding resources and nesting opportunities, promote weed invasion and increase opportunities for incursion by feral or introduced animals.

In future, severe impacts are anticipated from sea-level rise and more frequent extreme weather events associated with global climate change.

Recovery actions

  • 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 biology and ecology of the water mouse through research studies, ecological assessments and monitoring programs.
  • Promote population expansion by rehabilitating habitat adjacent to existing populations.
  • Implement community education 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 adjacent to 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.