Xeromys myoides 

Scope: Global

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Rodentia Muridae

Scientific Name: Xeromys myoides
Species Authority: Thomas, 1889
Common Name(s):
English Water Mouse, False Swamp Rat, False Water Rat, False Water-rat
French Faux Rat D'Eau
Spanish Rata Bastarda De Agua
Taxonomic Notes: The extent of morphological and genetic variation (and its taxonomic significance) across the markedly discontinuous range of Xeromys myoides is poorly resolved.

Assessment Information [top]

Red List Category & Criteria: Vulnerable B2ab(ii,iii,v) ver 3.1
Year Published: 2016
Date Assessed: 2015-07-25
Assessor(s): Woinarski, J. & Burbidge, A.A.
Reviewer(s): Amori, G.
Contributor(s): Winter, J., Aplin, K., Dickman, C., Ward, S. & Gynther, I.
Most parameters are poorly known for this species, and especially so for its New Guinea and Northern Territory range. However, in spite of its large extent of occurrence (EOO), it is plausible that its area of occupancy (AOO) is less than 2,000 km². Its distribution is severely fragmented, and there is also continuing decline in the area of occupancy, and the extent and quality of its habitat. Therefore the species is assessed as Vulnerable under criterion B2.

Based on small population size for some subpopulations, and the relatively few known subpopulations, the population size may be less than 10,000 individuals (but cannot be reliably estimated to be less than that threshold); no subpopulation has more than 1,000 individuals, and there is continuing decline in habitat quality and extent, and hence in population size.

Note that in a review of status of this species in Queensland, Dickman et al. (2000) considered that its status was Endangered there, noting that ‘its small and declining population and range size suggest that it is more at risk in Queensland than previously believed’. However, substantially more survey work has been conducted in Queensland since, revealing a far more extensive distribution than previously known, with sizeable (but less than 1,000 individuals) subpopulations at some sites (I. Gynther pers. comm).
Previously published Red List assessments:

Geographic Range [top]

Range Description:This little-known species is present on the island of New Guinea (Papua New Guinea only) and in northern Australia. On New Guinea, it is known only from a few specimens collected in the south-west Trans-Fly River region. In northern Australia, it has been recorded from several near-coastal sites in the Northern Territory (including Melville Island) and a discontinuous strip of the south-eastern and eastern Queensland coast (from about Proserpine in the north to near the New South Wales border in the south, and including Fraser, Bribie, North Stradbroke and South Stradbroke Islands) (Van Dyck 1997, Ball 2004, Gynther and Janetzki 2008, Russell and Hale 2009).It is likely to be more extensively distributed, but there has been relatively little intensive targeted sampling in areas between these known localities, and – in some regions – many searches in apparently suitable habitat have failed to record the species (Russell and Hale 2009).

For the Queensland component of its range, Dickman et al. (2000) considered that the ‘area has declined by an unknown extent’, largely due to coastal agriculture and residential development, resulting in loss or degradation of mangrove and coastal wetland habitat. In the Northern Territory, the few reports have been mostly single records (Redhead and McKean 1975, Magnussen et al. 1976, Woinarski et al. 2000), with little information about subsequent population persistence: one example is the sole record from (what is now) Kakadu National Park, in 1903 (Parker 1973, Woinarski et al. 2007).

Countries occurrence:
Australia (Northern Territory, Queensland); Papua New Guinea
Additional data:
Estimated area of occupancy (AOO) - km2:400-4000Continuing decline in area of occupancy (AOO):Yes
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:300000-500000
Continuing decline in extent of occurrence (EOO):YesExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:10-50Continuing decline in number of locations:Yes
Extreme fluctuations in the number of locations:No
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:There has been no robust assessment of population size; however Dickman et al. (2000) estimated the population size in Queensland to be between 1,000 and 10,000 individuals. For its Australian range, Gynther and Janetzki (2008) considered it ‘rare, scattered’.

For the Queensland component of its range, Dickman et al. (2000) considered that the population size was ‘suspected to be declining’, and Van Dyck and Gynther (2012) documented the recent extirpation of one subpopulation and the decline of another. For the Northern Territory component of its range, Woinarski et al. (2007) considered population trends were unknown. Woinarski et al. (2014) considered the Australian population to comprise 10,000 mature individuals (with low reliability) and to be declining.

Traill et al. (2011) used Population Viability Analysis (PVA) modelling to examine its responses to climate change (through sea level rise), increased development of coastal areas and predation by feral Cats, for south-eastern Queensland. Although this study noted some expected benefit through inland migration of mangrove vegetation, the overall model suggested extirpation in the region in ca 50 years.
Current Population Trend:Decreasing
Additional data:
Number of mature individuals:5000-50000Continuing decline of mature individuals:Yes
Extreme fluctuations:NoPopulation severely fragmented:Yes
No. of subpopulations:10-30Continuing decline in subpopulations:Yes
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:The Water Mouse is a nocturnal rodent with unusual habitat and diet characteristics. It occurs mostly in near coastal regions, with most records from mangroves (within inland edges of mangroves and on tidal flats) and some records from saline grasslands or sedgelands and near-coastal freshwater swamps (Van Dyck 1997, Woinarski et al. 2000, Ball 2004), or where there is a juxtaposition of these features (Russell and Hale 2009). It typically builds a distinctive mud dome nest (or set of burrows in earth banks sometimes with an additional mud dome), within which a dominant male and other animals may live communally (Van Dyck and Durbidge 1992, Van Dyck 1997, Van Dyck and Gynther 2003, Ball 2004). Other nests are constructed inside hollow tree trunks, usually mangroves, with mud sometimes visible at the base of the tree or sealing any openings in the trunk above ground level (Magnusson et al. 1976, Van Dyck and Gynther 2003, Gynther 2011).

The Water Mouse forages on the ground, in tidal flats, and around the water’s edge with most prey comprising invertebrates, including crabs, pulmonates and molluscs (Van Dyck 1997). Home range size averaged 0.6 ha in one Queensland study; and 3.4 ha at another site (Van Dyck 1997).

Little is known of breeding characteristics. Reproduction may occur throughout the year (Van Dyck 1997). Females produce up to four young (Gynther and Janetzki 2008). Age to maturity and longevity are unknown; generation length is assumed to be 2-3 years (Woinarski et al. 2014).

Systems:Terrestrial; Freshwater
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):2-3
Movement patterns:Not a Migrant

Use and Trade [top]

Use and Trade: Xeromys myoides is not utilized.

Threats [top]

Major Threat(s): The water Mouse is potentially threatened by the destruction of mangrove habitats, through reclamation projects and the development of marine aquaculture. Agriculture and development are a threat across swamp and wetland habitats. The species tends not to survive where there is development inland of mangrove areas. Across most of its range, wetland habitats are degraded by livestock and feral animals. Gynther and Janetzki (2008) name oil pollution, waste water treatment, acid sulphate contamination, alteration of natural hydrology, and chemical control of biting insects as major threats. Predation by feral Domestic Cats (Felis catus) may be a threat, but extent and impact are not known, and much of its preferred habitat is likely to be not appreciably used by cats. Threats in the New Guinea portion of range are not well defined. Climate change is likely to result in marked diminution of habitat extent and quality (Traill et al. 2011).

Conservation Actions [top]

Conservation Actions: This species is listed on Appendix I of CITES. This species is recorded from some reserves (e.g., Kakadu - although with no confirmed records there for more than 100 years). Habitat protection is a key conservation requirement for the species. Further studies into the distribution, taxonomy, and threats to the species are needed.

Citation: Woinarski, J. & Burbidge, A.A. 2016. Xeromys myoides. The IUCN Red List of Threatened Species 2016: e.T23141A22454469. . Downloaded on 28 October 2016.
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