Polynesian Rat

name = Polynesian Rat

status = LR/lc | status_system = IUCN2.3
regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Rodentia
familia = Muridae
subfamilia = Murinae
genus = "Rattus"
species = "R. exulans"
binomial = "Rattus exulans"
binomial_authority = (Peale, 1848)

range_map_caption = Polynesian Rat range in South-east Asia (in red)
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 most Polynesian islands, New Zealand, Fiji, and even 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 other rats like the Black and Brown Rats. It has large round ears, a pointed snout, black/brown hair with a lighter belly, but comparatively small feet. They have thin, long bodies, reaching up to in to cm|6 in length from the nose to the base of the tail, making them slightly smaller than other human-associative rats. Where they exist on smaller islands they tend to be smaller still (e.g. in to cm|4.5). They are commonly distinguished by a dark upper edge of the hind foot near the ankle. The rest of their foot is pale.

Distribution and habitat

The Polynesian Rat is widespread throughout the Pacific and South-east Asia. They cannot swim over long distances and are therefore considered to be a significant marker of the human migrations across the Pacific, as the Polynesians accidentally or deliberately introduced them 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 rats. It has also been suggested that the rats played a role in the complete deforestation of Easter Island by eating the nuts of the local palm tree, and thus preventing regrowth of the forest. [Flenley, John R. (2003) The enigmas of Easter Island]

Although remains of the Polynesian Rat in New Zealand were dated to over 2000 years old during the 1990s, [Holdaway, R.N. (1996). Arrival of rats in New Zealand, "Nature", 384, 225-226.] which was much earlier than the accepted dates for Polynesian migrations to New Zealand, this finding has been overturned by later research showing that the rat was introduced to both of the country's main islands around 1280 AD. [Janet M. Wilmshurst, Atholl J. Anderson, Thomas F. G. Higham, and Trevor H. Worthy (2008). [http://www.pnas.org/cgi/content/full/105/22/7676 Dating the late prehistoric dispersal of Polynesians to New Zealand using the commensal Pacific rat] , "Proceedings of the National Academy of Science", 105, 7676-7680.]


Polynesian Rats are nocturnal like most rodents, and are adept climbers, often nesting in trees. In winter, when food is scarce, it is common for them to 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 the fact that they do not breed year round, instead restricting it to spring and summer.


"R. exulans" is an omnivorous species: eating seeds, fruit, leaves, 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 in order 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.


*IUCN2006|assessors=Baillie, J.|year=1996|id=19330|title=Rattus exulans|downloaded=12 May 2006
*cite web|title=ISSG entry: Rattus exulans|url=http://www.issg.org/database/species/ecology.asp?si=170&fr=1&sts=sss|accessdate=2006-12-05

External links

*cite web |author=D. J. Campbell, I. A. E. Atkinson |date=1999 |title=Effects of kiore ("Rattus exulans" Peale) on recruitment of indigenous coastal trees on northern offshore islands of New Zealand |work=Journal of The Royal Society of New Zealand |publisher=Vol. 29 No 4, December 1999, pp. 265-290 |url=http://www.rsnz.org/publish/jrsnz/1999/18.pdf|accessdate=2007-06-17

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