Pacific rat: animal pest alert

Page last updated: Thursday, 3 May 2018 - 10:43am

This animal pest alert provides information on the identification, biology, and pest potential of the Pacific rat in Australia.

Introduction

The Pacific rat (Rattus exulans) is also known as the kiore, or Polynesian or Maori rat. It is not indigenous to Australia but has established populations in the wild on islands here and elsewhere in Asia and the South Pacific. It is closely associated with human settlement and is often accidently transported to new areas by people.

The Pacific rat poses an extreme threat to Australia. It has significant potential to establish more wild populations on islands and the mainland and become a pest.

It is very important that those travelling into Australian waters maintain quarantine measures against rats and immediately report any Pacific rats found here. Similarly, it is vital that persons visiting those Australian islands that currently support Pacific rat populations do not transport them to other islands or the mainland.

Description

The Pacific rat is a small mammal 8-14cm in length (head and body) and 30-100g in weight. The tail length is variable, often as long as or slightly longer than the body but it can also be shorter. The body fur is reddish-brown to grey-brown with translucent bristles buried in the fur and projecting black guard hairs on the back and sides; the fur feels somewhat harsh to touch. The belly fur is dark grey with white or pale grey tips. The thin, dark tail has short hairs on the upper surface and narrow rings of scales. The upper surface of each hind foot is marked with a triangle of dark reddish-brown hairs, extending from the ankle to part way down the foot. The toes are pale. The rat has a pointed nose and naked ears with dark grey skin.

Mistaken identity

In Australia, the Pacific rat may be mistaken for other rodents, but the table will help to distinguish adults from other species. Juvenile Pacific rats are similar to house mice (Mus musculus) apart from the tail colour; the rat’s tail is dark while the mouse’s tail is grey-brown. The feet of a juvenile Pacific rat are proportionally longer and broader than those of an equivalent-sized mouse. Pacific rats also have an elongated fleshy pad on the under surface of the feet whereas the pad is round shaped on mice.

Name and status;

Distribution

Ears

Body 
weight;

Fur

Tail

Hind foot;

Number of 
nipples

Droppings

Pacific rat 
(R. exulans)
Not indigenous 

 

On coastal islands 
in northern Australia. 
Associates with 
humans.

Smaller 
than 
black 
rat’s. 
Cover 
eyes if 
pulled 
forward.

30-100g

Reddish-to grey-

brown. Belly fur

dark grey with

white/light grey

tips. Dark hair

patch on upper

hind feet.

125-135mm
About the 
same as head/
body length,
thin and all 
dark.

24-31mm
 4 on each 
side of 
body; 2 on 
each side 
of lower 
abdomen.

6.4-9mm
Blunt ended

Bush rat 
(R. fuscipes
Indigenous 

 

Coastal areas of sw. 
and e. Australia. 
Does not associate 
with humans.

Do not 
cover 
eyes if 
pulled 
forward.

40-225g
 Variable-long soft
grey, shaggy dark
grey, short reddish
brown (longer and
softer than Norway
rat’s). Belly always
grey or cream.

105-195mm
 Slightly shorter 
than head/
body length; 
shorter than 
black rat’s; 
less scaly than 
Norway rat’s.

23-40mm
4-5 on 
each side of 
body; 3 on 
each side 
of lower 
abdomen

12mm (est.) 
One end 
pointed. Found 
at burrow 
entrances and 
on rat runways

Black or ship 
Rat (R. rattus
Not indigenous 

 

Coastal australia 
and on Australian 
islands. Associates 
with humans.

Cover 
eyes if 
pulled 
forward.

95-340g
Grey-brown to 
reddish-brown. 
Belly fur grey, 
white or cream 
often tinged 
yellowish.

185-245mm
 Variable, 
usually 10-30mm more 
than head/
body length; 
all dark.

30-40mm
5-6 on 
each side of 
body; 3 on 
each side 
of lower 
abdomen.

6.8-13.8mm
 Blunt ended. 
Deposited 
singly and 
scattered 
about

Norway or 
brown rat 
(R. norvegicus
Not indigenous

 

All areas except the 
NT. Associates with 
humans.

Do not 
cover 
eyes if 
pulled 
forward.

200-400g
 Grey-brown on 
back. appearing 
shaggy and bristly. 
Belly fur pale 
brown or grey. 
Black individuals 
occur.

150-215mm
Clearly 
shorter than 
head/body 
length; thick 
and usually 
with pale 
underside.

30-45mm
 6 on each 
side of 
body; 3 on 
each side 
of lower 
abdomen.

13.4-19.1mm
 One end 
pointed. 
Usually in 
groups, corners

and ledges.

Contact information

Pest and Disease Information Service (PaDIS)
+61 (0)8 9368 3080