Damage by the Pacific rat
The Pacific rat is considered a major pest of agriculture in some parts of mainland south-eastern Asia and its islands, Melanesia and throughout the Pacific region. Greatest damage is reported to rice and sugarcane crops and in Melanesia to tuber crops such as sweet potato. Other crops damaged include banana, cacao, coconut, maize, passionfruit, pawpaw, pineapple and root crops. A variety of damage occurs with flowers, pollen, fruit and seeds eaten, and stalks and other plant parts gnawed causing damage and increasing the plants’ susceptibility to infection and disease.
The Pacific rat is considered a moderate environmental pest, competing with, and predating on, indigenous wildlife and adversely affecting native forests.
Species of ground-nesting birds, reptiles and large flightless invertebrates have declined on some New Zealand offshore islands since the arrival of the Pacific rat, and it is considered responsible for the extinction of the greater short-tailed bat. On Norfolk Island the Pacific rat feeds on the eggs and nestlings of ground-nesting birds and it is likely that this contributed to the extinction of the burrow-nesting Providence petrel and Pycroft’s petrel. On this island it is also likely that the rat contributed to the extinction of the kaka parrot, Norfolk pigeon and Tasman starling. On Henderson Island (Pitcairn Islands) intense predation of newly-hatched chicks by Pacific rats was observed during a one year study of three species of petrels. On Green Island (Hawaii), Pacific rats were observed feeding on nesting Laysan albatrosses causing birds to die later from their injuries.
The Pacific rat also causes environmental damage to plants in New Zealand. Reduced recruitment of at least 11 tree species is reported and some have been made locally extinct due to rats eating plants, seeds and seedlings. Similarly, on Pacific islands the rat damages indigenous plants (including at least 15 threatened species) by eating plant parts and damaging bark.
On Viwa Island (Fiji), the Pacific rat enters homes, eats food and bites people while they sleep. The rat is also a significant public health risk in south-eastern Asia and the Pacific region as it is a vector of human diseases such as leptospirosis and scrub typhus, which can cause serious illness or death if not diagnosed and treated early.
Intensive eradication programs using toxic baits are used to remove Pacific rats from Australian, New Zealand and Pacific islands. In 2004, a program to eradicate rats from Adele Island was conducted by the state Department of Parks and Wildlife (formaly Department of Environment and Conservation), however it was unsuccessful.
Potential to be a pest in Australia
A scientific risk assessment of the Pacific rat was conducted by the Department of Primary Industries and Regional Development, Western Australia and endorsed by the national Invasive Plants and Animals Committee. It involved careful use of available information and application of the precautionary approach and indicates that the Pacific rat poses an extreme threat (the highest of four categories) to Australia. The risk assessment rated the rat as highly likely to establish further populations here as several areas of the country have climates similar to the rat’s overseas range. The extreme threat category assigned to this species indicates that once established, it could become a pest of agriculture, the environment and the community.
It is therefore important that the Pacific rat does not establish further populations in the wild in Australia and that any found here are removed quickly.
Pacific rats inhabit ecological niches similar to those of some Australian rodents and marsupials and these would be potentially at risk from competition for food, nesting sites and suitable habitat. The diet of the Pacific rat could include a wide range of indigenous plants and animals, including animals larger than itself. For example, ground-nesting birds and their eggs and chicks could be at risk from predation. Agricultural crops that could be at risk include cereals, flowers, fruit (such as grapes, pineapples and passionfruit), legumes, nuts, oil seeds, sugarcane and vegetables.
The Pacific rat often lives in close association with humans so it could spread diseases such as leptospirosis. By damaging gardens, foodstuffs and electrical wiring it could also add to the nuisance already caused in urban areas by other pest rodents.
Declared pest category
The Western Australian Organism List (WAOL) contains information on the area(s) in which this pest is declared and the control and keeping categories to which it has been assigned in WA. Use the links on this page to reach Pacific rat in WAOL.
Pacific rats in the wild and risk management
The Pacific rat is prohibited from import into Australia but it could arrive here accidentally. To prevent the rat from establishing populations in the wild here and becoming a pest, it is essential that all those involved in importing cargo into Australia ensure that rodents do not board ships and transport barges at the point of departure. Any animals found on board should be eliminated to ensure they do not disembark here, and management strategies should be in place at likely entry points to detect, contain and eradicate rats.
Any Pacific rats detected should also be immediately reported to the nearest relevant government department or wildlife authority on Freecall 1800 084 881 so that appropriate action can be taken.