Distribution
The natural range of the Pacific rat was probably parts of Indochina but it is not well-defined because of its transportation by people throughout the Pacific region in prehistoric times. Its current range includes southern and south-eastern Asia from eastern Bangladesh, the Andaman Islands, Burma, Thailand, Vietnam, Taiwan, south to the Greater and Lesser Sunda Islands (Sumatra to West Papua), Papua New Guinea (including the Bismarck Archipelago), the Solomon Islands, the Philippines, New Zealand and many of the islands of Micronesia and Polynesia.
Invasion pathways
Pacific rats were introduced to many Pacific islands including Hawaii and New Zealand by early Polynesian colonists, either as accidental stowaways or deliberately as a food source.
In recent times, accidental stowaways on vessels have been considered the source of new infestations in Australia.
The earliest records of the Pacific rat in Australia are from Adele Island (northern Western Australia) in 1891. The rat is believed to have been translocated on fishing vessels from Indonesia during the nineteenth century or earlier, and from Murray Island (east of the Torres Strait) in 1888–89 (probably introduced by early canoeists from Papua). Currently, the Pacific rat occurs on these two islands as well as Norfolk Island. It may also occur on Sunday island (Western Australia) and Christmas Island (Commonwealth). Pacific rats have not been recorded on mainland Australia.
Habitat
In Asia the Pacific rat lives in close association with people around villages and in huts or houses, cultivated fields, rice paddies, coconut plantations and canefields. In Pacific Island villages the black rat generally displaces the Pacific rat to the forests or, if the black rat occurs in high numbers, the Pacific rat may be absent. The Pacific rat also inhabits cleared areas with good cover, grassland, bush, scrub and secondary forest. On Adele Island it lives in spinifex hummock grassland completely away from human habitation.
Reproduction, food and behaviour
The Pacific rat breeds throughout the year with increased activity between October and June. In New Zealand, breeding is from September to March. Pacific rats usually have three litters per year, typically of four young, but litter size can vary from one to nine. The neat, spherical nest is usually built about 20cm off the ground among debris, often at the base of trees, in and under logs and sometimes in trees and buildings. Nests can be suspended in ‘tussock’ grasses including rice plants and cane grass.
The Pacific rat is omnivorous, eating seeds, flowers, fruits and other plant parts, snails, insects and larvae, earthworms, lizards and birds, their eggs and chicks. Pacific rats often carry food to small husking stations that provide shelter from predators, competitors and the elements during feeding.
The Pacific rat is nocturnal but when population density is high, activity begins just before dark and daytime activity has been observed on Pacific Islands. It lives mainly on the ground but also climbs tall grasses, low trees and along village walls and roofs. Data from New Zealand indicates the Pacific rat is only able to swim an average of 65m, while black rats average 300m or greater and Norway rats 600m.
The life expectancy of the Pacific rat in the wild is less than one year.