Polynesian Rat (Rattus exulans)


The Polynesian rat, or Pacific rat (Rattus exulans), known to the Māori as kiore, is the third most widespread species of rat in the world behind the brown rat and black rat. The Polynesian rat originates in Southeast Asia, but like its cousins, has become well travelled – infiltrating Fiji and most Polynesian islands, including New Zealand, Easter Island and Hawaii. It shares the ability to easily adapt to many different types of environments, from grasslands to forests. Its habits are also similar, becoming closely associated with humans because of the easy access to food. As a result, it has become a major pest in almost all areas within its distribution. The Polynesian rat is similar in appearance to the black, or ship, rat (Rattus rattus), but smaller. Its fur is brown-grey on the back, with the underside a light grey. The tail is uniformly dark. Females have four pairs of teats. Body plus head length: 110-130mm. Tail length: 120 to 150mm. Weight: usually 60-80g, but animals of up to 180g have been found. The animals on small islands, such as the Hawaiian islands, are smaller, weighing only 37 to 39g.he Polynesian rat is similar in appearance to other rats, such as the black rat and the brown rat. It has large, round ears, a pointed snout, black/brown hair with a lighter belly, and comparatively small feet. It has a thin, long body, reaching up to 6 inches (15 cm) in length from the nose to the base of the tail, making it slightly smaller than other human-associative rats. Where it exists on smaller islands, it tends to be smaller still [e.g. 4.5 inches (11 cm)]. It is commonly distinguished by a dark upper edge of the hind foot near the ankle. The rest of its foot is pale.


he Polynesian rat is widespread throughout the Pacific and Southeast Asia. It cannot swim over long distances, so is therefore considered to be a significant marker of the human migrations across the Pacific, as the Polynesians accidentally or deliberately introduced it to the islands they settled. The species has been implicated in many of the extinctions that occurred in the Pacific amongst the native birds and insects; these species had evolved in the absence of mammals and were unable to cope with the predation pressure posed by the rat. This rat also may have played a role in the complete deforestation of Easter Island by eating the nuts of the local palm tree, thus preventing regrowth of the forest. Although remains of the Polynesian rat in New Zealand were dated to over 2000 years old during the 1990s, which was much earlier than the accepted dates for Polynesian migrations to New Zealand, this finding has been overturned by later research showing the rat was introduced to both of the country's main islands around 1280 AD. They are found from Bangladesh to Vietnam, throughout the East Indies and on many Pacific islands including Easter Island, Hawaii and New Zealand. Their distribution is so wide because they have been introduced both accidentally and deliberately by people to many of these places. Native range: The Pacific rat is native to Southeast Asia.
Present in India, Indonesia, Japan, Malaysia, Myanmar/Burma, Thailand, Philippines, Taiwan, USA, Chile, Australia, New Zealand, Papua New Guinea, American Samoa, Cook Islands, Fiji, French Polynesia, Guam, Kiribati, Marshall Islands, Federated States of Micronesia, Nauru, New Caledonia, Niue, Northern Mariana Islands, Palau, Pitcairn, Samoa, Solomon Islands, Tokelau, Tonga, Tuvalu, Vanuata, Wallis and Futuna, and US minor outlying islands. It has dispersed with humans across the Western and central Pacific. They occur from the Asiatic mainland south to New Guinea and New Zealand, and east to the Hawaiian Islands and Easter Island. R. exulans may have been present in the Mariana Islands for at least 3500 years, introduced by the Chamorro people. There appear to be no island groups that were reached by the Polynesians that did not receive Rattus exulans. However, a number of islands within groups, particularly those uninhabited, are still free of it (Atkinson and Atkinson, 2000).

American Samoa (American Samoa); Brunei Darussalam; Christmas Island; Cocos (Keeling) Islands; Cook Islands; Fiji; French Polynesia; Guam; Kiribati; Marshall Islands; Nauru; New Caledonia; New Zealand; Niue; Norfolk Island; Northern Mariana Islands; Palau; Papua New Guinea; Philippines; Samoa; Singapore; Solomon Islands; Timor-Leste; Tokelau; Tonga; Tuvalu; United States (Hawaiian Is.); United States Minor Outlying Islands; Vanuatu; Wallis and Futuna

They are found in a wide variety of habitats, including grasslands, scrublands, scrub and various types of forest. In Southeast Asia the Polynesian rat has a very close association with people, inhabiting houses and rice fields.


Polynesian rats are omnivorous, eating insects, centipedes, spiders, worms, snails, fruit, seeds, leaves and roots. Sometimes they eat lizards and birds or strip bark from saplings. bark, insects, earthworms, spiders, lizards, avian eggs and hatchlings. Polynesian rats have been observed to often take pieces of food back to a safe place to properly shell a seed or otherwise prepare certain foods. This not only protects them from predators, but also from rain and other rats. These "husking stations" are often found among trees, near the roots, in fissures of the trunk, and even in the top branches. In New Zealand, for instance, such stations are found under rock piles and fronds shed by nikau palms. They are considered pests in many places, as they feed on sugar cane, coconuts, cocoa and other crops. Polynesian rats are nocturnal like most rodents, and are adept climbers, often nesting in trees. In winter, when food is scarce, they commonly strip bark for consumption and satisfy themselves with plant stems.


Polynesian rats are nocturnal, starting to become active around dusk or just after. They are agile climbers and sometimes nest and feed in trees. Each rat has a small home range of up to 280m diameter. Females avoid each other in the breeding season.


Females are capable of having up to 13 litters per year, but 1 to 3 litters is normal for wild populations. Gestation period is 19 to 30 days. Litters are normally born in the summer. There are 2 to 5 offspring per litter, and these are weaned when 2 to 3 weeks old. They have common rat characteristics regarding reproduction: polyoestrous, , litter size affected by food and other resources (6–11 pups), weaning takes around another month at 28 days. They diverge only in that they do not breed year round, instead being restricted to spring and summer. Placental, sexual. Females are polyoestrous and ovulate spontaneously. Breeding largely determined by food availability. Litter size normally 6 - 11, gestation is 21-24 days, young weaned at about 28 days. Females can be sexually active in the season of their birth, and can have up to six litters a year (Wittenberg, R. (ed.) 2005). In New Zealand, the Norway rat has been observed breeding throughout the year (Innes, 2001).

Lifecycle stages:

Gestation 19-21 days. Weaning 2-4 weeks. Sexual maturity 8-12 months, though maturity can be achieved during the same season as birth (Atkinson and Moller 1990). In captivity: Gestation minimum 23 days. Weaning 2-3 weeks. Sexual maturity 60-70 days (Tobin 1994). Total life is estimated between 12 - 15 months. Pacific rats have been observed to mature earlier and survive better, with some adults surviving to a second breeding season, where high quality food and year-round shelter were available (Atkinson and Towns, 2001). Strong seasonal fluctuations occur in the density of kiore populations on New Zealand’s northern offshore islands. Breeding is restricted to spring and summer, so densities reach a peak in autumn, then decline to low levels in spring (Campbell et al., 1984).

Major Threat(s):

There are no major threats to this species.

 Conservation Actions:

It is presumably present in many protected areas.

Conservation status

Polynesian rats are not listed by the IUCN.

Polynesian rats carry various diseases that are transmittable to humans, including plague and leptospirosis.