Polynesian rat

The Polynesian rat, Pacific rat or little rat (Rattus exulans), or kiore, is the third most widespread species of rat in the world behind the brown rat and black rat. Contrary to its vernacular name, the Polynesian rat originated in Southeast Asia, and like its relatives has become widespread, migrating to most of Polynesia, including New Zealand, Easter Island, and Hawaii. It shares high adaptability with other rat species extending to many environments, from grasslands to forests. It is also closely associated with humans, who provide easy access to food. It has become a major pest in most areas of its distribution.

Quick Facts Polynesian rat Temporal range: Holocene, Conservation status ...

Polynesian rat Temporal range: Holocene
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Rodentia
Family:	Muridae
Genus:	Rattus
Species:	R. exulans
Binomial name
Rattus exulans (Peale, 1848)
Polynesian rat native range in Southeast Asia (in red) (note: the IUCN Red List instead considers it introduced throughout all of its Pacific islands range, as well as Brunei, Singapore, and the Philippines)

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The 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 15 cm (5.9 in) in length from the nose to the base of the tail, making it slightly smaller than other human-associated rats. Where it exists on smaller islands, it tends to be smaller still – 11.5 cm (4.5 in). It is commonly distinguished by a dark upper edge of the hind foot near the ankle; the rest of its foot is pale.^[2]

The Polynesian rat is widespread throughout the Pacific and Southeast Asia. Mitochondrial DNA analysis suggests that the species originated on the island of Flores.^[3] The IUCN Red List considers it native to Bangladesh, all of mainland Southeast Asia, and Indonesia, but introduced to all of its Pacific range (including the island of New Guinea), the Philippines, Brunei, and Singapore, and of uncertain origin in Taiwan.^[4] It cannot swim over long distances, so is 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 pressures 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 Paschalococos, thus preventing regrowth of the forest.^[5][6]

Although remains of the Polynesian rat in New Zealand were dated to over 2,000 years old during the 1990s,^[7] which was much earlier than the accepted dates for Polynesian migrations to New Zealand, this finding has been challenged by later research showing the rat was introduced to both the country's main islands circa 1280.^[8]

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. They have common rat characteristics regarding reproduction: polyestrous, with gestations of 21–24 days, 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.