| Polynesian rat | |
|---|---|
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Rodentia |
| Family: | Muridae |
| Subfamily: | Murinae |
| Genus: | Rattus |
| Species: | R. exulans |
| Binomial name | |
| Rattus exulans (Peale, 1848) |
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| 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 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.
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The Polynesian rat is similar in appearance to other rats like the black rat and the brown rat. It has large round ears, a pointed snout, black/brown hair with a lighter belly, but comparatively small feet. It has thin, long bodies, 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.
The Polynesian rat is widespread throughout the Pacific and South-east Asia. It cannot swim over long distances and 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. It has also been suggested that the rat may have 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.[2]
Although remains of the Polynesian rat in New Zealand were dated to over 2000 years old during the 1990s,[3] 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 AD 1280.[4]
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.
In New Zealand and its offshore islands, many bird species evolved in the absence of terrestrial mammalian predators and developed no behavioral defenses to rats. The introduction by the Maori of the Polynesian Rat into New Zealand resulted in the eradication of several species of terrestrial and small seabirds.
Subsequent elimination of rats from islands has resulted in substantial increases in populations of certain seabirds and endemic terrestrial birds. As part of its program to restore populations of sea birds and endemic terrestrial birds such as the endangered kakapo, the New Zealand Department of Conservation undertakes programs to eliminate the Polynesian rat on most offshore islands in its jurisdiction and other conservation groups have adopted similar programs in other reserves seeking to be predator- and rat-free.[5]
However, two islands in the Hen and Chickens group, Mauitaha and Araara, have now been set aside as sanctuaries for the Polynesian rat.[6]