Western chestnut mouse (Pseudomys nanus)

Captive western chestnut mouse
IUCN Red List species status – Least Concern LEAST

Top facts

  • The western chestnut mouse inhabits grasslands and open woodlands, where it feeds on grasses and seeds.
  • The western chestnut mouse usually breeds in response to rainfall.
  • The gestation period of the western chestnut mouse is quite short compared to that of related species.
  • After birth, the young western chestnut mice cling to the female’s nipples, being carried about as she moves around.
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Western chestnut mouse fact file

Western chestnut mouse description

GenusPseudomys (1)

The western chestnut mouse (Pseudomys nanus) is a small Australian rodent with light orange-brown fur (2) (5). Its fur is soft (4), and is white on the belly and light brown on the ears (2) (5).

The body of the western chestnut mouse is relatively robust (3), with short limbs and small, rounded ears (2). The tail is narrow (2) and only moderately haired (4).

The western chestnut mouse shows significant sexual dimorphism in body size, with the male being larger than the female (3).

Also known as
Barrow Island chestnut mouse.
Head-body length: 8 - 14 cm (2)
Tail length: 7 - 12 cm (2)
Male weight: up to 73 g (3)
Female weight: up to 63 g (3)

Western chestnut mouse biology

A largely nocturnal species (2) (4), the western chestnut mouse shelters in a grass nest during the day (2). Its diet consists mainly of grass and seeds (2).

Although the western chestnut mouse can breed year-round if conditions are favourable, most breeding occurs in response to rainfall, often taking place during the wet season (2) (3). Breeding activity may then tail off again towards the end of the dry season, when food resources become scarce (3).

The female western chestnut mouse gives birth to between 3 and 5 young (1) (2) (4), after a relatively short gestation period of 22 to 24 days (1) (5). As in many native Australian rodents, the young mice are likely to cling to the female’s nipples for much of the time, being carried around as she moves about (3) (4) (5). The female western chestnut mouse is likely to mate again soon after giving birth (3).

Young western chestnut mice mature quickly, with some females able to start breeding from about 40 days old. This means that the young may be able to breed in the same season in which they were born (5).

Unlike some related species, the western chestnut mouse is not believed to be particularly social, and males can be aggressive towards each other (5).


Western chestnut mouse range

The western chestnut mouse is found in northern Australia, where it occurs in the Northern Territory and Western Australia. Its distribution stretches from Barrow Island in the west to the Sir Edward Pellew Group of Islands in the east (1) (5).

This species was formerly more widespread in Western Australia, but is now thought to have been lost from the southern parts of its range there (1) (5).

On Barrow Island, off the coast of Western Australia, the western chestnut mouse has sometimes been referred to as the ‘Barrow Island chestnut mouse’. However, recent genetic evidence has shown that this island form is not a separate subspecies (2).


Western chestnut mouse habitat

The western chestnut mouse mainly inhabits grasslands and the grassy undercover of open woodlands (1) (3) (5).


Western chestnut mouse status

The western chestnut mouse is classified as Least Concern (LC) on the IUCN Red List (1).

IUCN Red List species status – Least Concern


Western chestnut mouse threats

The western chestnut mouse is abundant and widespread, and is not currently believed to be facing any major threats. However, its population is slowly declining, and any future changes to fire regimes or to levels of grazing in its habitat could potentially pose a threat to this species (1).

Some Pseudomys species have been negatively affected by introduced predators and competitors (4), but it is not known whether introduced species are affecting the western chestnut mouse population at present.


Western chestnut mouse conservation

This small rodent occurs in a number of protected areas, including the nature reserves of Potter Island and Sholl Island (1). Barrow Island is also a nature reserve, and although gas and oil extraction are occurring there, management plans are in place and efforts are being made to protect the island’s wildlife and wild habitats. All mammal species on Barrow Island are protected, including the western chestnut mouse (2).

No specific conservation measures are currently known to be in place for the western chestnut mouse, but further research has been recommended into its populations, its response to fires, and the potential threats it may face (1).


Find out more

Find out more about the western chestnut mouse and other mammals on Barrow Island:

More information on conservation in Australia:



This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:



The state of being pregnant; the period from conception to birth.
Active at night.
Sexual dimorphism
When males and females of the same species differ in appearance.
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.


  1. IUCN Red List (August, 2012)
  2. Moro, D. and MacAulay, I. (2010) A Guide to the Mammals of Barrow Island. Chevron Australia, Perth. Available at:
  3. Taylor, J.M. and Calaby, J.H. (2004) Reproductive strategies of Pseudomys nanus and Pseudomys delicatulus (Rodentia: Muridae) from the monsoonal tropics of the Northern Territory. Australian Journal of Zoology, 52: 271-282.
  4. Nowak, R.M. (1991) Walker’s Mammals of the World. The Johns Hopkins University Press, Baltimore and London.
  5. Breed, B. and Ford, F. (2007) Native Mice and Rats. CSIRO Publishing, Collingwood, Victoria.

Image credit

Captive western chestnut mouse  
Captive western chestnut mouse

© John Cancalosi / naturepl.com

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