Broad-toothed mouse  (Mastacomys fuscus)

The broad-toothed mouse is classified as Near Threatened (LC) on the IUCN Red List (1).

A tubby, compact rodent that is endemic to south-eastern Australia, the broad-toothed mouse (Mastacomys fuscus) earns its common name from its wide incisors and molar teeth, which are used to grind grasses (2) (3). This miniscule mammal has a short, wide face, and a relatively short tail, which is ringed and largely naked (3). The small, rounded ears are covered in tiny, sandy-brown hairs (2). The coat of the broad-toothed mouse is sandy-brown to dark brown on the upperparts (2), often tinged with attractive reddish highlights (3), and there are long, black guard hairs on the back. The fur on the underparts is pale grey to buff-grey, and the feet are dusky brown (2).

Endemic to south-eastern Australia, the broad-toothed mouse is found in the Snowy Mountains of New South Wales and the Australian Capital Territory, Barrington Tops in New South Wales, the Eastern Highlands, Victorian Alps, Otway Ranges, and Wilsons Promontory in Victoria (1). It also occurs in western Tasmania (4).

The broad-toothed mouse inhabits high altitude subalpine areas with moderate to dense cover of grasses and sedges, such as heathland, as well as clearings in wet sclerophyll forests, or wet sedgelands along streams in valley floors. Its habitat tends to be characterised by high rainfall, a cool climate, areas of cover, such as boulders, shrubs or grass tussocks, and access to grasses that form the majority of its diet (1). Snow covers the broad-toothed mouse’s habitat for around four months of the year (5).

A specialist herbivore, the broad-toothed mouse feeds almost entirely on grasses and sedges of the families Poaceae and Cyperaceae, although seeds and mosses are also eaten (2) (3). Food is mainly gathered at night during summer and autumn, but during the afternoon and early evening in winter (3). The broad-toothed mouse lives in a complex of runways through dense vegetation, with these relatively warm tunnels enabling it to remain active during the winter, when snow covers its habitat (3). 

The broad-toothed mouse has a complex social organisation, being solitary in summer months and communal in winter (5) (6). It is most active in January and February and least active in winter, when it is often found huddled for warmth in mixed-sex groups in nests, built in dense grasses or under logs (3). 

Breeding takes place in spring and summer, when the female broad-toothed mouse produces two litters of one to four young (1) (2). The gestation period is around 35 days. Mating for the first litter occurs in mid to late October and the first litter is born in late November or early December. Mating for the second litter then takes place in late December or early January, with the young born in late February or early March (6). The female broad-toothed mouse is territorial during the breeding season, driving males away after the young are born (2)

Restricted to isolated populations by the sparseness of its habitat, the broad-toothed mouse is at risk from habitat loss, as well as other threats, such as climate change and predation by introduced mammals (1). 

Across many parts of its range, the broad-toothed mouse has suffered significant population declines. At Mount Kosciuszko, this species’ population has declined by over 50 percent, most likely due to low snow cover and early snow melt, possibly associated with climate change. Decreased snow cover can lead to higher levels of predation by foxes and feral cats. There is also some evidence to suggest that foxes preferentially prey upon the broad-toothed mouse over other rats and mice in its habitat, perhaps because it occurs in family groups or because it is slower and less aggressive than other rats or mice (2) (7). These threats were compounded by a bush fire in January 2003 that burned approximately 70 percent of the alpine area where this species occurs. In addition, the broad-toothed mouse has not been recorded in the Otway Ranges for the last 30 years (1). 

The broad-toothed mouse is particularly vulnerable to the adverse affects of climate change as it is a high altitude specialist (1). It is expected to retreat to higher altitudes in response to climate change; however, where this is not possible, the broad-toothed mouse is at great risk from rapid habitat loss. There is also the potential for it to be exposed to increased competition with native rat species, which are likely to expand in range as the climate changes (8). 

Other threats to the broad-toothed mouse include habitat conversion to ski resort developments and habitat destruction and degradation by feral horses, rabbits, hares, pigs. Introduced weeds such as broom species (Cytisus) and an exotic grass, Holcus lanatus, are invading this species’ habitat at Barrington Tops, while willow species (Salix) are a threat in alpine Victoria. In Tasmania, inappropriate fire regimes are a potential threat to the broad-toothed mouse (1).

The broad-toothed mouse is afforded a degree of protection in a number of parks and reserves, including Kosciuszko National Park, Barrington Tops National Park, Victoria's Alpine National Park, Wilsons Promontory National Park and possibly Great Otway National Park, as well as several other protected areas in New South Wales and the Australian Capital Territory. In Tasmania, the broad-toothed mouse is well protected as more than half of its habitat is within the Tasmanian Wilderness World Heritage Area (1). 

The isolated population of the broad-toothed mouse at Barrington Tops has received extra attention by its listing as an Endangered Population under the Threatened Species Conservation Act 1995 (1). As a result, numerous recovery plans have been put in place for this population, including fox control programmes each winter, cat control around ski resorts and pig and weed control. Feral horse removal and predator proof fencing is also being considered (1). 

Other conservation recommendations for the broad-toothed mouse include controlling rabbits and hares that degrade its habitat, the use of traps to remove invasive mammals, the control of exotic weeds, such as brooms at Barrington Tops. Mapping this species’ habitat, such that bush fire control and forest management may be more sympathetic to its habitat requirements,  would also be beneficial, as well as surveys for the broad-toothed mouse in alpine areas where developments are proposed (3). Further research is also required to understand more about the broad-toothed mouse’s biology and population status, as well as further research into the species’ ability to respond to threats such as competition with introduced rats and climate change (1).

Find out more about conservation in Australia:

• Australian Wildlife Conservancy:
  http://www.australianwildlife.org/