The Polynesian rat, Pacific rat or little rat (''Rattus exulans''), known to the
Māori
Māori or Maori can refer to:
Relating to the Māori people
* Māori people of New Zealand, or members of that group
* Māori language, the language of the Māori people of New Zealand
* Māori culture
* Cook Islanders, the Māori people of the C ...
as ''kiore'', is the third most widespread species of
rat
Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include ''Neotoma'' ( pack rats), ''Bandicota'' (bandicoot ...
in the world behind the
brown rat and
black rat
The black rat (''Rattus rattus''), also known as the roof rat, ship rat, or house rat, is a common long-tailed rodent of the stereotypical rat genus ''Rattus'', in the subfamily Murinae. It likely originated in the Indian subcontinent, but is n ...
. 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
Pest or The Pest may refer to:
Science and medicine
* Pest (organism), an animal or plant deemed to be detrimental to humans or human concerns
** Weed, a plant considered undesirable
* Infectious disease, an illness resulting from an infection
** ...
in most areas of its distribution.
Description
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 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 – . It is commonly distinguished by a dark upper edge of the hind foot near the ankle; the rest of its foot is pale.
Distribution and habitat
The Polynesian rat is widespread throughout the
Pacific and
Southeast Asia.
Mitochondrial DNA
Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
analysis suggests that the species originated on the island of
Flores
Flores is one of the Lesser Sunda Islands, a group of islands in the eastern half of Indonesia. Including the Komodo Islands off its west coast (but excluding the Solor Archipelago to the east of Flores), the land area is 15,530.58 km2, and th ...
. The
IUCN Red List considers it native to
Bangladesh, all of
mainland Southeast Asia
Mainland Southeast Asia, also known as the Indochinese Peninsula or Indochina, is the continental portion of Southeast Asia. It lies east of the Indian subcontinent and south of Mainland China and is bordered by the Indian Ocean to the west an ...
, 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. 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
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s 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.
Although remains of the Polynesian rat in New Zealand were dated to over 2,000 years old during the 1990s, 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 around A.D. 1280.
Behaviour
Polynesian rats are
nocturnal
Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.
Nocturnal creatures generally have highly developed sens ...
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
The estrous cycle (, originally ) is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous p ...
, 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.
Diet
''R. exulans'' is an
omnivorous species, eating seeds, fruit, leaves, bark, insects, earthworms, spiders, lizards, and 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.
Rat control and bird conservation
New Zealand
In New Zealand and its offshore islands, many bird species evolved in the absence of terrestrial mammalian predators, so developed no behavioral defenses to rats. The introduction by the Māori 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 well as species of insects such as the
Little Barrier Island giant wētā. As part of its program to restore these populations, such as the critically endangered
kākāpō, 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.
However, two islands in the
Hen and Chickens group, Mauitaha and Araara, have now been set aside as sanctuaries for the Polynesian rat.
Rest of the Pacific
NZAID
The New Zealand Aid Programme is the New Zealand Government's international aid and development agency. The New Zealand Aid Programme is managed by the Pacific and Development Group in the New Zealand Ministry of Foreign Affairs and Trade (MFAT) ...
has funded rat eradication programs in the
Phoenix Islands of
Kiribati in order to protect the bird species of the
Phoenix Islands Protected Area.
Between July and November 2011, a partnership of the Pitcairn Islands Government and the
Royal Society for the Protection of Birds implemented a poison baiting programme on
Henderson Island aimed at eradicating the Polynesian rat. Mortality was massive, but of the 50,000 to 100,000 population, 60 to 80 individuals survived and the population has now fully recovered.
References
*
External links
*
*
{{Taxonbar, from=Q339418
Rattus
Rodents of Oceania
Rodents of India
Mammals of Bangladesh
Rodents of New Guinea
Mammals of Southeast Asia
Mammals of New Zealand
Mammals of Indonesia
Mammals described in 1848
Introduced animals of Hawaii
Stored-product pests
Taxa named by Titian Peale