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   Rattus exulans (mammal) français   
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         General Impact

    Atkinson and Towns (2001) report numerous species of New Zealand flora and fauna that are vulnerable to Pacific rats (Rattus exulans). Most vulnerable amongst invertebrates are large, flightless species; especially those that need to descend to ground level for part of their life-cycle. Lizard populations have also been shown to increase following the removal of Rattus exulans. In Hawai'i and New Zealand there are examples of detrimental effects on both burrowing petrels and on red-tailed tropicbirds. In the Leeward Islands of Hawai'i, it has been shown that predation on seabirds only becomes significant after storms have reduced the fruiting of food plants. Fatal attacks by R. exulans on adult Laysan albatrosses appear likely to be associated with the same factor. R. exulans is also known to browse native flora (including trees, shrubs, fungi, sedges, grasses, orchids and other herbaceous plants and lianes), although the magnitude of such effects has been difficult to determine (Atkinson and Atkinson, 2000).

    R. exulans is a major agricultural pest throughout Southeast Asia and the Pacific region. Crops damaged by this species include rice, maize, sugarcane, coconut, cacao, pineapple, and root crops.




         Location Specific Impacts:
    Aitutaki Is. (Cook Islands) English 
    Agricultural: Pacific rats (Rattus exulans) are a problem for the copra crop and for mangoes.
    Atiu (`Atiu) Is. (Cook Islands) English 
    Agricultural: Pacific rats (Rattus exulans) cause problems for mango and pineapple crops.
    Manihiki Is. (Cook Islands) English 
    Agricultural: Pacific rats (Rattus exulans) cause problems for the copra crop.
    Pukapuka Is. (Cook Islands) English 
    Agricultural: Pacific rats (Rattus exulans) cause problems for the copra crop.
    Ahnd (Ant) Atoll (Micronesia, Federated States of (FSM)) English 
    Reduction in native biodiversity: Pacific rats (Rattus exulans) prey on birds, turtle eggs, coconut crabs and hundreds of other small land creatures that inhabit the atoll, consequently reducing biodiversity of the atoll.
    Ouvea Is. (New Caledonia (Nouvelle Caledonie)) français  English 
    Threat to endangered species: Today the Pacific rat represents an additional threat to the horned parakeet of Ouvea (see Eunymphicus cornutus in the IUCN Red List of Threatened Species), which is already threatened with extinction because of loss of habitat and capture for the pet trade (Robinet et al. 1998).
    New Zealand English 
    Ecosystem change: Possible effects of Pacific rats (Rattus exulans) on selected indigenous tree species in coastal forests of northern New Zealand are surveyed from recent field sampling and a literature review. Recruitment rates are compared on islands with and without Pacific rats: (i) on the same island before or at the time of rat eradication compared with recruitment some years later, and (ii) on geographically separated islands with and without Pacific rats. In addition, Pacific rats-proof exclosures enabled some comparisons to be made of seed germination and survival in the presence and absence of Pacific rats. There is evidence that Pacific rats have substantially reduced recruitment of Pittosporum crassifolium, Pouteria costata, Streblus banksii, and Nestegis apetala, by eating the seed. Seed consumption and/or depressed recruitment is demonstrated for Rhopalostylis sapida, Vitex lucens and Pisonia brunoniana, but the extent of recruitment reduction is not yet clear. No depressive effect by Pacific rats on the recruitment of some species, including Dysoxylum spectabile, Beilschmiedia tawa, B. tarairi, Corynocarpus laevigatus, Melicytus ramiflorus, Pseudopanax arboreus, P. lessonii, and Coprosma macrocarpa, has yet been demonstrated; juveniles remain abundant in the presence of Pacific rats. Some tree species most affected by Pacific rats are now rare in coastal forest of the northern islands and mainland. Evidence from recruitment reduction in these species suggests that the composition of northern coastal forest before Pacific rats arrived was significantly different from that of the present. It also suggests that, if rats are present, current successional pathways following burning or other disturbance of coastal forest will not restore the forest to its pre-human composition (Campbell and Atkinson, 1999).

    Reduction in native biodiversity: Finsch’s duck (Chenonetta finschi), an extinct, possibly flightless New Zealand endemic, was widely distributed and apparently abundant immediately before human settlement of New Zealand, but its bones have rarely been identified in archaeological sites. Its extinction has been variously attributed to habitat changes, predation by the introduced Pacific rat (R. exulans), and human predation (Holdaway et al 2002).
    Henderson Is. (Pitcairn) English 
    Predation: Brook (1995) recorded intense predation by Pacific rats (Rattus exulans) on newly hatched Murphy’s and Kermadec petrel chicks.
    Henderson Is. (Pitcairn) English 
    Threat to endangered species: Rattus exulans predate on newly hatched chicks of the 'Near Threatened (NT)' Murphy's petrel (see Pterodroma ultima in IUCN Red List of Threatened Species) and Kermadec petrels (Pterodroma neglecta) on Henderson (Brooke, 1995 in Varnham, 2006) Survival of several species of petrel is 'severely threatened' by rat predation (Vickery, 1994 in Varnham, 2006).

    Threat to endangered species: Rattus exulans predate on newly hatched chicks of the 'Near Threatened (NT)' Murphy's petrel (see Pterodroma ultima in IUCN Red List of Threatened Species) and Kermadec petrels (Pterodroma neglecta) on Henderson (Brooke, 1995 in Varnham, 2006) Survival of several species of petrel is 'severely threatened' by rat predation (Vickery, 1994 in Varnham, 2006).
    Pitcairn English 
    Agricultural: Pacific rats (Rattus exulans) attack citrus fruit trees on Pitcairn (Moverly 1953, in Varnham 2005).

    Predation: Pacific rats (Rattus exulans) predate on newly hatched chicks of Murphy's and Kermadec petrels on Henderson (Brooke 1995, in Varnham 2005). Survival of several species of petrel is 'severely threatened' by rat predation (Vickery 1994, in Varnham 2005). A risk of reintroduicng rats to Ducie from Pitcairn is mentioned by (Brooke et al. 2003, in Varnham 2005).

    Reduction in native biodiversity: Survival of several species of petrel is "severely threatened by predation from the introduced Pacific rat (SPREP, 2000).
    Pitcairn English 
    Agricultural: Rattus exulans attack citrus fruit trees on Pitcairn (Moverly, 1953 in Varnham, 2006)

    Agricultural: Rattus exulans attack citrus fruit trees on Pitcairn (Moverly, 1953 in Varnham, 2006)
    Hawaii (Hawai‘i) Is. (United States (USA)) English 
    Agricultural: Pacific rats (Rattus exulans) are a major agricultural pest throughout Southeast Asia and the Pacific region. Crops damaged by this species include rice, maize, sug-arcane, coconut, cacao, pineapple, and root crops. In the United States, sugarcane is the only crop of economic concern damaged by Polynesian rats. The most severe damage is to unirrigated sugarcane on the windward side of the islands of Hawaii and Kauai. Here, rats find excellent habitat in the lush vegetation of noncrop lands adjacent to sugarcane fields.
    Rat damage to Hawaiian sugarcane is negligible until the crop is 14 to 15 months old, after which it increases substantially and progressively until harvest.Injury ranges from barely perceptible nicks in the outer rind to neatly chiseled canoe shaped cavities. Small chips usually are evident on the ground where rats have fed, (Prevention And Control Of Wildlife Damage,1994).
    Kure Atoll (United States (USA)) English 
    Predation: Fleet and Woodward have shown that predation on seabirds only becomes significant after storms have reduced the fruiting of food plants. Fatal attacks by Pacific rats on adult Laysan albatrosses (Kepler 1967) appear likely to be associated with the same factor (Atkinson and Moller, 1990).
    Hawaii (United States (USA)) English 
    Agricultural: Pacific rats (Rattus exulans) are a major agricultural pest throughout Southeast Asia and the Pacific region. Crops damaged by this species include rice, maize, sug-arcane, coconut, cacao, pineapple, and root crops. In the United States, sugarcane is the only crop of economic concern damaged by Polynesian rats. The most severe damage is to unirrigated sugarcane on the windward side of the islands of Hawaii and Kauai. Here, rats find excellent habitat in the lush vegetation of noncrop lands adjacent to sugarcane fields.
    Rat damage to Hawaiian sugarcane is negligible until the crop is 14 to 15 months old, after which it increases substantially and progressively until harvest.Injury ranges from barely perceptible nicks in the outer rind to neatly chiseled canoe shaped cavities. Small chips usually are evident on the ground where rats have fed, (Prevention And Control Of Wildlife Damage,1994).

    Economic/Livelihoods: The economic impact of damage of sugarcane by Pacific rats (Rattus exulans) fluctuates from year to year, largely dependent on the prevailing price of sugar. In 1980, when the average price of raw sugar was at a 50-year high, the Hawaiian sugarcane industry may have lost $20 million. Current losses are conservatively estimated to be greater than $6 million annually (Prevention And Control Of Wildlife Damage,1994).
    Howland Island (United States Minor Outlying Islands) English 
    Human nuisance



ISSG Landcare Research NBII IUCN University of Auckland