The Polynesian rat, also called the Pacific rat or little rat (Rattus exulans), or kiore, is the third most common rat species in the world, after the brown rat and black rat. Even though its common name suggests otherwise, this rat originally came from Southeast Asia. Like other rats, it has spread widely, traveling to most parts of Polynesia, including New Zealand, Easter Island, and Hawaii. It can live in many different places, such as grasslands and forests. This rat is closely linked to humans, who provide it with easy access to food. It has become a major pest in most areas where it lives.
Description
The Polynesian rat looks similar to other rats, such as the black rat and the brown rat. It has large, round ears, a pointed nose, black or brown fur with a lighter-colored belly, and small feet. Its body is thin and long, measuring up to 15 cm (5.9 in) from the nose to the base of the tail, which makes it slightly smaller than other rats that live near humans. On smaller islands, these rats are even smaller, reaching about 11.5 cm (4.5 in) in length. A key feature that helps identify the Polynesian rat is the dark color on the top of its hind foot near the ankle, while the rest of the foot is pale.
Distribution and habitat
The Polynesian rat lives in many places across the Pacific and Southeast Asia. Studies of DNA suggest that the species first appeared on the island of Flores. The IUCN Red List lists it as native to Bangladesh, all of mainland Southeast Asia, and Indonesia, but as introduced to all of its Pacific range (including New Guinea), the Philippines, Brunei, and Singapore. Its origin in Taiwan is unknown. This rat cannot swim long distances, so it is considered an important sign of human movement across the Pacific, as Polynesians likely brought it to the islands they settled. The species has been linked to many extinctions of native birds and insects in the Pacific. These animals evolved without mammals and could not survive the threats from the rat. This rat may also have contributed to the loss of forests on Easter Island by eating the nuts of the local palm tree, Paschalococos, which stopped the forest from growing back.
Although remains of the Polynesian rat in New Zealand were found to be more than 2,000 years old in the 1990s, this date was much earlier than the accepted time when Polynesians arrived in New Zealand. Later research has questioned this finding, showing that the rat was introduced to both of New Zealand’s main islands around the year 1280.
Behaviour
Polynesian rats are active at night, like many other rodents, and are skilled climbers who often build nests in trees. During winter, when food is limited, they remove bark from trees to eat and also consume plant stems. Their reproduction habits are similar to other rats: they can reproduce multiple times a year, with pregnancies lasting 21–24 days. The number of babies in each litter depends on food availability and other resources, typically ranging from 6 to 11 pups. These pups are weaned and independent after about 28 days. However, Polynesian rats differ from other rats by only breeding during spring and summer, not throughout the year.
R. exulans is an omnivorous species, meaning it eats both plants and animals. Its diet includes seeds, fruit, leaves, bark, insects, earthworms, spiders, lizards, and bird eggs and young. Polynesian rats are often seen carrying food to safe places to properly prepare it, such as shelling seeds. This behavior helps protect them from predators, rain, and other rats. These special food preparation spots, called "husking stations," are commonly found near tree roots, in tree trunks, or in branches. In New Zealand, these stations are also found under rock piles and beneath the fronds of nīkau palms.
Rat control and bird conservation
In New Zealand and its nearby islands, many bird species lived without land-based mammal predators, so they did not develop ways to protect themselves from rats. When the Māori people brought the Polynesian rat to New Zealand, several species of land and small seabirds disappeared.
Removing rats from islands has helped some seabirds, land birds, and insects, like the Little Barrier Island giant wētā, grow in numbers. To help birds like the critically endangered kākāpō, the New Zealand Department of Conservation runs programs to remove Polynesian rats from most offshore islands. Other groups also work to make their areas free of predators and rats.
However, two islands in the Hen and Chickens group, Mauitaha and Araara, are now protected areas where Polynesian rats are allowed to live.
NZAID has supported rat removal programs in the Phoenix Islands of Kiribati to protect the birds there.
Between July and November 2011, the Pitcairn Islands Government and the Royal Society for the Protection of Birds used poison bait to remove Polynesian rats from Henderson Island. Many rats died, but about 60 to 80 out of 50,000 to 100,000 survived. The rat population has now fully recovered.