Broad-Toothed Mouse, Broad-Toothed Rat, Mastacomys fuscus, Mastacomys fuscus mordicus
Vulnerable (Species Profile and Threats Database / Australia. Dept of Environment and Energy)
How wild horses threaten the broad-toothed mouse
The numbers of these mice have declined in areas where wild horse trampling and tracks have destroyed the sheltered runways that these mice use to access food and water. Tracks made by wild horses have allowed foxes to hunt these mice more easily.
There are many studies on the effect of wild horses on the places in which broad-toothed mice live. Here are summaries of a couple.
Survey by Forestry Corporation of NSW
In 2011 the Forestry Corporation of NSW, Riverina Region, funded a survey of broad-toothed mice (then referred to as broad-toothed rats) in state forests between Tumut and Cabramurra. The study found heavy grazing and trampling in over 36 places where the mice were living. Both horses and cattle contributed to the grazing, but horses were more often present than cattle - 95% to 65% ratio in one forest and 85% to 25% in another forest.
The survey also found that broad-toothed mice numbers were highest in ungrazed and lightly grazed areas, and concluded: '... despite being widespread, the long-term survival of M. fuscus in Buccleuch, Bago and Maragle State Forests is dependent upon the control of introduced herbivores, particularly feral horses and by excluding cattle grazing in wetlands'.
C.A. Belcher and D. Leslie. Broad-toothed Rat Mastacomys fuscus distribution in Buccleuch, Bago and Maragle State Forests, NSW in Australian zoologist 35 (3), 2011, pages 555-559.
Survey by NPWS and University of Canberra
In 2002, ecologists from the National Parks and Wildlife Service of NSW and the University of Canberra surveyed broad-toothed mice in the Snowy Mountains. At each study site, they recorded whether both mice and horses were present or absent.
At that time, they found 'no evidence of hard-hoofed herbivores' above 1500 metres. They did, however, find evidence of wild horses below 1500 metres in the plains and frost hollows in the northern parts of Kosciuszko National Park. And there they noted that broad-toothed mice were mostly absent; the only places they were present were small areas of grassland where fallen logs prevented access by horses.
They concluded that 'rabbits and hard-hoofed herbivores were responsible for damaging native vegetation, opening up inter-tussock areas where M. fuscus normally constructed runways'.
K. Green and W.S. Osborne. The Distribution and Status of the Broad-toothed Rat Mastacomys fuscus (Rodentia: Muridae) in New South Wales and the Australian Capital Territory in Australian Zoologist 32 (2) 2003, pages 229-237.