Plains Rat

## Description

The plains rat (Pseudomys australis), also known as the palyoora, plains mouse and eastern mouse, is a conilurine rodent native to arid and semi-arid Australia. Referred to as the pallyoora or yarlie by Indigenous groups, the plains rat was once widely distributed across central Australia, including north-west New South Wales and south-west Queensland; however, habitat degradation due to grazing, introduced predators and drought have contributed to its decline. Consequently, the plains rat has been listed as 'presumed extinct' in New South Wales and Victoria, 'endangered' in the Northern Territory and Queensland and 'vulnerable' in Western Australia and South Australia. While recent research has indicated the presence of the plains rat in areas such as the Fowlers Gap and Strzelecki Desert regions of New South Wales and within the Diamantina National Park in Queensland, there are only five sub-populations currently recognised nationally, none of which coincide with recent discoveries of the plains rat. As the current population trend of the plains rat has been listed as 'declining' by the International Union for the Conservation of Nature (IUCN), the IUCN conservation status for the species is 'vulnerable'.

## Appearance

Plains rats are one of the largest rodents in the arid zone of Australia. They have a stocky body with long ears and a rounded muzzle. Fur color is grey to brown along the animal's back with white or cream lining its underbelly. These mice have long ears and a rounded snout and their tail is roughly as long as their body.

## Distribution

Plains rats are native to Australia. They occur in five broad geographic zones: the Arcoona Tableland, South Australia; the Southern Lake Eyre region, South Australia; the Moon Plain region, South Australia; the Oodnadatta region (including Witjira National Park), South Australia/Northern Territory; and the Andado Station and Mac Clark Conservation Reserve, Northern Territory. These animals inhabit gibber deserts (stony deserts), flood plains, with low shrubs and hard clayplains.

## Behavior

Plains rats are social animals. During non-breeding periods males and females live together in colonies of up to 20 individuals; however, during breeding periods one male occupies a burrow with up to three females. During breeding cycles males become very agitated and both sexes are known to stand on their hind feet and squeal loudly when threatened. Plains rat construct a complex system of shallow connected tunnels beneath the cracking clay of gibber plains, emerging only at night to feed. The home range of an adult is roughly 1.6 hectares.

## Diet

Plains rats are mainly herbivorous. They feed on seeds, stems and ocassionally arthropods.

## Reproduction

Plains rats are polygynous. This means that males have many partners during a breeding season. These rats don't have a regular breeding season and usually reproduce after a period of rainfall. Females give birth to four young; however up to seven young can be produced in one litter. The gestation period lasts 30-31 days. During lactation, females can be seen dragging their young as they each latch to one of the four teats located on mother's underbelly. The young become weaned at around 28 days after birth and reach reproductive maturity at 8-10 weeks of age.

## Population

### Population threats

Main threats to Plains rats are habitat degradation, introduced predators and drought. Habitat degradation mainly derives from introduced hoofed stock and land clearing. Hoofed stock lessen vegetation cover, crush the seed bank and trample burrows while land clearing removes food sources vital to the survival of the Plains rat. Reduced vegetation cover and damaged burrows only makes it easier for introduced predators such as the European fox and Feral cat to excavate shallow burrows. This can contribute to local extinctions, particularly when populations are already low during periods of drought. Other potential threats to Plains rat include altered fire regimes, leading to increased intensity of bushfires; competition with the introduced House mouse and European rabbit and climate change.

### Population number

According to the IUCN Red List, the total population size of Plains rats is 5,000-20,000 mature individuals. This species’ numbers are decreasing and it is currently classified as Vulnerable (VU) on the IUCN Red List.