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         General Impact

    The ship rat has directly caused or contributed to the extinction of many species of wildlife including birds, small mammals, reptiles, invertebrates, and plants, especially on islands. Ship rats are omnivorous and capable of eating a wide range of plant and animal foods. These include native snails, beetles, spiders, moths, stick insects and cicadas and the fruit of many different plants (Innes 1990). They also prey on the eggs and young of forest birds (Innes et al., 1999). In the recovery programme for the endangered Rarotonga flycatcher or kakerori (see Pomarea dimidiata in the IUCN Red List of Threatened Species), Robertson et al. (1994) identified ship rats as the most important predator affecting the breeding success of this bird. Several cases are known where predation on seabirds can be reliably attributed to ship rats. These include sooty terns (see Sterna fuscata in IUCN Red List of Threatened Species) in the Seychelles Islands (Feare, 1979), Bonin petrels (see Pterodroma hypoleuca in IUCN Red List of Threatened Species) in Hawai'i (Grant et al., 1981), Galapagos dark-rumped petrels (see Pterodroma phaeopygia in IUCN Red List of Threatened Species) in the Galapagos Islands (Harris, 1970), and white-tailed tropicbirds (see Phaethon lepturus in IUCN Red List of Threatened Species) in Bermuda (Gross, 1912).

    The ship rat is most frequently identified with catastrophic declines of birds on islands. The best documented examples in the Pacific region are Midway Island in the Leeward Islands of Hawai'i (Johnson, 1945; Fisher and Baldwin, 1946), Lord Howe Island (Hindwood, 1940; Recher and Clark, 1974) and Big South Cape Island, New Zealand (Atkinson and Bell, 1973). Atkinson (1977) brought together circumstantial evidence suggesting that ship rats, rather than disease, were responsible for the decline of many species of Hawai'ian native birds during the 19th century.

    There are few indications of rat-induced declines in native birds on islands nearer the equator (latitude 15°N to 20°S). This zone coincides with the distribution of native land crabs, animals that also prey on birds and their eggs. The long co-existence between land crabs and some island birds may have resulted in the development of behaviours among the birds that gives them a degree of protection against rats. Atkinson (1985) suggested that this might be the reason why rat-induced catastrophes are less apparent within the equatorial zone, but this hypothesis has never been tested (SPREP, 2000).

    Species of weight similar to or smaller than that of rats appear to be the most vulnerable to predation. Impacts also appear to be more severe on smaller islands, where rat densities tend to be higher and do not fluctuate. Constant predation pressure results in a reduction in colony size on these islands (Martin et al., 2000).

    Both R. rattus and R. norvegicus transmit the plague bacterium (Yersinia pestis) via fleas in certain areas of the world. There have been a series of recent outbreaks in Madagascar in recent years (Boiser et al. 2002).




         Location Specific Impacts:
    Green Is. (Antigua and Barbuda) English 
    Predation: In the late 1990s a large Rattus rattus population had become established on Green Island and within a very short time it had eradicated the endemic and critically endangered Antiguan Racer (Alsophis antiguae). Only 100 individuals were left on a tiny neighbouring island. Seabirds, hummingbirds, pigeons, tree seedlings, seaturtles nesting sites and endemic reptiles of Anolis and Ameiva were also depleted by the rats with enormous speed.
    Lord Howe Is. (Australia) English 
    Predation: The ship rat is most frequently identified with catastrophic declines of birds on islands (Hindwood 1940, Recher and Clark 1974).
    Bermuda English 
    Predation: White-tailed tropicbird predation can be reliably attributed to ship rats (Gross 1912).
    Bermuda English 
    Interaction with other invasive species: Black rats, Rattus rattus assist in the spread of the invasive Chinese fan palm (Livistonia chinensis).

    Threat to endangered species: Black rats, Rattus rattus are known to preferentially eat seeds of the 'Endangered (EN) Bermuda palmetto, (see Sabal bermudana in IUCN Red List of Threatened Species).
    R. rattus are thought to predate on the 'Critically Endangered (CR)' endemic Bermuda skink (see Eumeces longirostris in IUCN Red List of Threatened Species) also found on offshore islands.(Anderson et al., 2001 in Varnham, 2006).
    They are likely to also predate wide variety of other species including endemic invertebrates (25 of which are 'Critically Endangered (CR)' (Glasspool, 2003 in Varnham, 2006). Black rats are also likely to predate Audubon's shearwaters (Puffinus lherminieri), the 'Endangered (EN)' blacked-capped petrels (see Pterodroma hasitata in IUCN Red List of Threatened Species); the 'Endangered (EN) Cahow petrels (see Pterodroma cahow in IUCN Red List of Threatened Species) if it reached their nesting islands (strongly implicated in their decline on mainland, and known to predate similar burrow nesting seabirds) (in Atkinson, 1985 in Varnham, 2006).
    Diego Garcia (British Indian Ocean Territory (BIOT)) English 
    Predation: Seabird nest density on most rat infested islands is significantly lower than on rat-free islands. On some islands 30-40% of eggs in sooty tern colonies show signs of rat predation (Symens, 1999 in Varnham, 2006).

    Threat to endangered species: Turtle nesting populations likely to be at risk (Mortimer and Day, 1999 in Varnham, 2006). The 'Critically Endangered (CR)' Hawksbill turtles (see Eretmochelys imbricata in IUCN Red List of Threatened Species) and the 'Endangered (EN)' green turtle (see Chelonia mydas in IUCN Red List of Threatened Species) nest on Diego Garcia.
    Eagle Is. (British Indian Ocean Territory (BIOT)) English 
    Other: The ship rat is present in large numbers and there are concerns that these predators may have major impacts on the islands ecosystem, by suppressing regeneration of native vegetation, through predation of sea turtle and seabird eggs and competition with the coconut crab (see Birgus latro in IUCN Red List of Threatened Species) for food resourses.
    Eagle Is. (British Indian Ocean Territory (BIOT)) English 
    Predation: Seabird nest density on most rat infested islands is significantly lower than on rat-free islands. On some islands 30-40% of eggs in sooty tern colonies show signs of rat predation (Symens, 1999 in Varnham, 2006).

    Threat to endangered species: Turtle nesting populations likely to be at risk (Mortimer and Day, 1999 in Varnham, 2006). The 'Critically Endangered (CR)' Hawksbill turtles (see Eretmochelys imbricata in IUCN Red List of Threatened Species) and the 'Endangered (EN)' green turtle (see Chelonia mydas in IUCN Red List of Threatened Species) nest on Diego Garcia.
    Cayman Brac (Cayman Islands) English 
    Reduction in native biodiversity: Black rat, Rattus rattus, is implicated in the extinction of a number of native species of small mammals, birds and reptiles (Morgan, 1994 in Varnham, 2006).
    Grand Cayman (Cayman Islands) English 
    Reduction in native biodiversity: Black rat, Rattus rattus, is implicated in the extinction of a number of native species of small mammals, birds and reptiles (Morgan, 1994 in Varnham, 2006).
    Little Cayman (Cayman Islands) English 
    Reduction in native biodiversity: Black rat, Rattus rattus, is implicated in the extinction of a number of native species of small mammals, birds and reptiles (Morgan, 1994 in Varnham, 2006).
    Sandy Cay (Cayman Islands) English 
    Herbivory: On Sandy Cay (nr Tortola), rats were seen eating a variety of plant material, especially growing tips of shrubs and small tree (Varnham, 2003 in Varnham, 2006).
    Galapagos Islands (Ecuador) English 
    Predation: Galapagos dark-rumped petrel predation can be reliably attributed to ship rats (Harris 1970).
    Falkland Islands (Malvinas) (sub-Antarctic) English 
    Habitat alteration: Black rats may have impacts on vegetation.

    Reduction in native biodiversity: Black rats have major adverse impacts on seabird and songbird populations.
    Clipperton Is. (France) français  English 
    Predation: The impact of the black rat (Rattus rattus) is difficult to quantify because of a lack of historical data. It has nevertheless been shown that the black rat use all the available food resources on the island. Thus it could be a predator of the eggs and chicks of certain species of seabirds.
    Europa Is. (French Southern Territories) français  English 
    Predation: The impact of Rattus rattus on the receiving ecosystems of the îles Eparses is not documented. It could nevertheless exert pressure on the nests of birds and juvenile turtles through direct predation. Its negative impact on vegetation is very likely.
    Glorioso Is. (French Southern Territories) français  English 
    Predation: The impact of Rattus rattus on the receiving ecosystems of the îles Eparses is not documented. It could nevertheless exert pressure on the nests of birds and juvenile turtles through direct predation. Its negative impact on vegetation is very likely.
    Juan de Nova Is. (French Southern Territories) français  English 
    Predation: The impact of Rattus rattus on the receiving ecosystems of the îles Eparses is not documented. It could nevertheless exert pressure on the nests of birds and juvenile turtles through direct predation. Its negative impact on vegetation is very likely.
    Guadeloupe français  English 
    Agricultural: Rats are well known as pests of crops, particularly sugar cane. The Plant Protection Department of Guadeloupe estimates 5% annual production losses in banana plantations and food crops (in Pascal et al., 2004a).

    Competition: Two species of rat, Rattus rattus et Rattus norvegicus, are suspected to have participated in the extinction of 3 endemic rodent species of the French Antilles (in Lorvelec et al., 2001).

    Disease transmission: Rodents are vectors and hosts of leptospirosis whose prevalence is 40 times higher in Martinique and Guadeloupe than in metropolitan France ( in Lorvelec et al., 2004).
    Fajou Is. (Guadeloupe) English 
    Predation: The mongose eradication, and the sharp decline in the ship rat population, ended the destruction of hawksbill turtle nests (see Eretmochelys imbricata in IUCN Red List of Threatened Species), and led to a re-colinisation of the dryer parts of the island by the clapper rail (Rallus longirostris), which had been strictly confined to the mangroves. The abundance indicies of the clapper rail and the terresrial crab Cardisoma guanhumi increased. More data is required to test the actual relationship between these increases and the reduction in alien mammal populations (Lorvelec, O., et al. 2004).
    Sangalaki Is. (Indonesia) English 
    Predation: Ship rats have eaten the eggs of green turtles (see Chelonia mydas in the IUCN Red List of Threatened Species) as well as hatchlings on their way to the sea. Often whole nests (containing around 80 eggs/hatchlings) were terminated completely in a matter of minutes. Also juvenile turtles were hunted by the rats and killed instantly or wounded deadly by pulling out their intestines. The soft shell of the turtles didn’t offer any protection. Survival rate of the attacked nests or hatchlings were at best 10 % but mostly tended to be zero, allowing no hatchling to reach the comparable safety of the sea (Images available in InGrip-Report).

    Unknown: Up to five grey imperial-pigeons (see Ducula pickeringii in IUCN Red List of Threatened Species) have been sighted on Sangalaki, which is around 100 km east of East-Kalimantan in the Derawan-Island group, by the invasive species eradication team. The grey imperial-pigeon is classified as vulnerable and specialises in inhabiting small islands with fig trees. Neighbouring islands with suitable habitat probably hold populations of grey imperial-pigeons, although they are likely to be threatened by hunting and deforestation. The few birds on Sangalaki, however, are safe now because the island is strictly protected as an important nesting ground for green turtles Chelonia mydas, and the rat eradication was successful (Meier, Guntram., 2004.).
    Martinique français  English 
    Agricultural: Rats have been identified as pests of crops, particularly that of cane sugar. A study in Martinique has assessed the loss attributable to rodents at 40% of turnover per hectare (in Pascal et al., 2004a).

    Competition: Rattus rattus and Rattus norvegicus are suspected of having participated in the extinction of endemic rodents (in Lorvelec et al., 2001).

    Disease transmission: Rodents are vectors and hosts of leptospirosis whose prevalence is 40 times higher in Martinique and Guadeloupe than in metropolitan France (in Lorvelec et al., 2004).

    Predation: The impact of Rattus rattus has been identified and quantified on the islets of Saint Anne. It reduces by 30% to 100% the flight success of several species of seabirds and also reduces the abundance index of certain terrestrial carcinofauna species such as the zombie crab (Gecarcinus ruricola) (Pascal et al., 2004b).
    San Jorge East Is. (Mexico) English 
    Predation: Craveri's Murrelet Synthliboramphus craveri) is listed as 'Vulnerable (VU)' in the IUCN Red List of Threatened Species. It has a small breeding range, It breeds on Islas Partida, Tiburón, San Jorge, San Esteban, Estanque, San Pedro Mártir, San Pedro Nolasco, San Francisco, Espíritu Santo and San Ildefonso, and possibly on the Pacific coast of Baja California, north to Islas San Benitos. Introduced predators mainly cats (Felis catus), black rats (Rattus rattus) and Deer mice (Peromyscus maniculatus) to some extent predate on adults and chicks, and have caused declines in population numbers. Craveri's Murrelet was most probably extirpated from the San Jorge's islands due to predation by introduced mammals (BirdLife International 2010)
    San Jorge Middle Is. (Mexico) English 
    Predation: Craveri's Murrelet Synthliboramphus craveri) is listed as 'Vulnerable (VU)' in the IUCN Red List of Threatened Species. It has a small breeding range, It breeds on Islas Partida, Tiburón, San Jorge, San Esteban, Estanque, San Pedro Mártir, San Pedro Nolasco, San Francisco, Espíritu Santo and San Ildefonso, and possibly on the Pacific coast of Baja California, north to Islas San Benitos. Introduced predators mainly cats (Felis catus), black rats (Rattus rattus) and Deer mice (Peromyscus maniculatus) to some extent predate on adults and chicks, and have caused declines in population numbers. Craveri's Murrelet was most probably extirpated from the San Jorge's islands due to predation by introduced mammals (BirdLife International 2010)
    San Jorge West Is. (Mexico) English 
    Predation: Craveri's Murrelet Synthliboramphus craveri) is listed as 'Vulnerable (VU)' in the IUCN Red List of Threatened Species. It has a small breeding range, It breeds on Islas Partida, Tiburón, San Jorge, San Esteban, Estanque, San Pedro Mártir, San Pedro Nolasco, San Francisco, Espíritu Santo and San Ildefonso, and possibly on the Pacific coast of Baja California, north to Islas San Benitos. Introduced predators mainly cats (Felis catus), black rats (Rattus rattus) and Deer mice (Peromyscus maniculatus) to some extent predate on adults and chicks, and have caused declines in population numbers. Craveri's Murrelet was most probably extirpated from the San Jorge's islands due to predation by introduced mammals (BirdLife International 2010)
    Montserrat English 
    Agricultural: Rats are also considered to be major agricultural and public health pests (Hilton, 2004 in Varnham, 2006).

    Disease transmission: Rats are also considered to be major agricultural and public health pests (Hilton, 2004 in Varnham, 2006).

    Ecosystem change: Rattus rattus can affect forest ecology through predation of seeds, fruits, flowers, seedlings and invertebrates (Hilton, 2004 in Varnham, 2006).

    Reduction in native biodiversity: Rattus rattus is likely to be significant predator of other birds and herptiles (some endemic).

    Threat to endangered species: Rattus rattus is known to predate nests of the 'Vulnerable (VU)' forest thrush (seee Cichlherminia lherminieri in IUCN Red List of Threatened Species) and the 'Critically Endangered (CR)' endemic Montserrat oriole (see Icterus oberi in IUCN Red List of Threatened Species). Rat predation is a major factor in the decline of the oriole in recent years (Hilton, 2004 in Varnham, 2006).
    R. rattus are known to attack and kill mountain chicken the near-endemic 'Critically Endangered (CR)' (see Leptodactylus fallax in IUCN Red List of Threatened Species) though the population impact is not known (Hilton, 2004 in Varnham, 2006).
    Kayangel Is. (Palau) English 
    Disease transmission: Ship rats are known to affect community health in Palau by acting as disease vectors, exposing citizens to gastrointestinal illnesses and leptospirosis through water supplies.

    Economic/Livelihoods: Ship rats are causing economic losses by damaging crops including papaya and corn.

    Threat to endangered species: Ground birds such as the Micronesian megapode (see Megapodius laperouse in the IUCN Red List of Threatened Species) are particularly vulnerable to introduced predators such as rats and cats.
    Ascension Is. (Saint Helena) English 
    Competition: The black rat, Rattus rattus is known to compete for food with natve land crabs (Ashmole and Ashmole, 2000 in Varnham, 2006).

    Reduction in native biodiversity: Management Plan suggests rats may be affecting the ability of smaller sea bird species to recolonise the island, as well as having a negative impact on native plants and invertebrates (Pickup, 1999 in Varnham, 2006).

    Threat to endangered species: The black rat, Rattus rattus is known to predate turtle hatchlings (128); believed to have caused the extinction of the Madeiran petrel (Pickup, 1999 in Varnham, 2006) and may predate sooty tern eggs or young (Hughes, 2004 in Varnham, 2006).
    Tristan da Cunha Is. (sub-Antarctic) (Saint Helena) English 
    Disease transmission: Ship rats pose an as yet un-quantified risk to human health on the island. At least one person is known to have required antibiotic treatment after a rat bite. People on Tristan are in general concerned about the potential for rats to spread disease on the island.

    Economic/Livelihoods: The growing of potatoes as a staple food crop is a fundamental aspect of Tristan life. Rats cause major problems for stored potatoes. Rats often damage seed potato stores, and the seed potatoes required for each year’s crop have to be held in rodent-proof wire cages. Similarly, potatoes for consumption are usually stored in sheds within the settlement, and are prone to rat feeding damage and to contamination through soiling from rat urine and faeces. Rats also feed on other island crops (e.g. pumpkins). The school and supermarket have had ongoing problems with rodent infestation, requiring closures for poisoning.

    Reduction in native biodiversity: It appears that populations of small seabirds on Tristan have been dramatically reduced through the impacts of rats over the past 120 years. Firm evidence of rat predation on broad-billed prion (see Pachyptila vittata in IUCN red List of Threatened Species) eggs has been found on the island. It is likely that if rats remain on Tristan, the populations of seabirds will continue to decline. This will be a major biodiversity loss, as Tristan itself is the only known breeding site within the Tristan archipelago for at least four species of seabirds.

    Threat to endangered species: The endemic Tristan thrush (see Nesocichla eremita in IUCN Red List of Threatened Species) (locally known as the ‘starchy’) is almost certainly affected by rat predation. Thrush nests tend to be constructed on or near the ground, making them highly vulnerable to rat predation. The relative scarcity of thrushes on Tristan in comparison to their abundance on the nearby rodent-free islands of Nightingale and Inaccessible is strongly suggestive of the effects of rodent predation. If rodents were inadvertently introduced to these islands, the impacts would potentially be devastating, especially for birds such as the flightless Inaccessible rail.
    Rats are probably affecting the breeding success of the 'Vulnerable' Atlantic petrel (see Pterodroma incerta in IUCN Red List of Threatened Species) (IUCN, 2007). It is likely that the Tristan moorhen (see Gallinula nesiotis in IUCN Red List of Threatened Species) was extirpated from Tristan as a result of predation by black rat, combined with feral cat predation, habitat loss and hunting by islanders. The successful establishment of the 'Vulnerable' Gough moorhen (see Gallinula comeri in IUCN Red List of Threatened Species) on Tristan suggests that it is able to cope with current levels of rat predation (IUCN, 2007).
    Tristan da Cunha Is. (sub-Antarctic) (Saint Helena) English 
    Agricultural: Black rats, Rattus rattus are important agricultural and food storage pests on Tristan (Hilton, 2004 in Varnham, 2006).

    Reduction in native biodiversity: Massive reductions of storm petrels (Pelagodroma marina) and Prions (Pachyptila forsteri) can be attributed to predation by cats (now eliminated) and rats.

    Threat to endangered species: Black rat, Rattus rattus are likely to be preventing some seabirds from successfully recolonising Tristan, and also to be major predators of the island's landbirds, notably the 'Near Threatened (NT)' rare Tristan thrush (see Nesocichla eremita> in IUCN Red List of Threatened Species) (Hilton, 2004 in Varnham, 2006).
    Saint Helena English 
    Disease transmission: Black rat, Rattus rattus is known to carry Weil's disease which can affect humans (Ashmole and Ashmole, 2000 in Varnham, 2006).

    Reduction in native biodiversity: Black rat, Rattus rattus is highly omnivorous, eating plants, invertebrates, young birds and especially fruit and vegetables (Ashmole and Ashmole, 2000 in Varnham, 2006).
    Sao Tome and Principe English 
    Predation: The Guinea Lidless Skink (see Afroablepharus africana) is classified as 'Vulnerable (VU)' in the IUCN Red List of Threatened Species. It is restricted to three location on the islands of Sâo Tomé, Principé, and Rolas in the Gulf of Guinea. The main threats to this species are suspected to be loss of habitat through deforestation and predation by introduced mammals. Introduced mammals on these islands include the African civet, Norway rat (Rattus norvegicus), ship rat (Rattus rattus), house mouse (Mus musculus), Mona monkey (Cercopithecus mona) and weasel (Mustela nivalis) (Ineich 2010).

    Predation: Declining populations of three endemic and 'Critically Endangered (CR)' birds the Sao Tome Ibis (see Bostrychia bocagei); the Sao Tome Canary (see Neospiza concolor) and the Sao Tome Fiscal (see Lanius newtoni) are under threat of loss of habitat and potential predation by introduced mammals that include the African civet (Civettictis civetta), ship rat (Rattus rattus), house mouse (Mus musculus), Mona monkey (Cercopithecus mona) and weasel (Mustela nivalis) (BirdLife International 2009; BirdLife International 2010; BirdLife International 2011). Feral pigs are also present and could be a threat (BirdLife International 2010).
    Seychelles English 
    Predation: Sooty tern predation can be reliably attributed to ship rats (Feare 1979).
    Central Valley (United States (USA)) English 
    Predation: Rattus rattus preys on songbird nests in old growth riparian forests in California's Central Valley.
    Anacapa West (United States (USA)) English 
    Competition: Rattus rattus competed with the native deer mouse (see Peromyscus maniculatus ssp. anacapae in IUCN Red List of Threatened Species) for food resources on Anacapa Island (National Park Service, 2006).

    Herbivory: Rattus rattus on West Anacapa Island ate most of the acorns from the island oak (National Park Service, 2006).

    Predation: Rattus rattus had almost extirpated Xantus's murrelet (see Synthliboramphus hypoleucus in IUCN Red List of Threatened Species) from Anacapa prior to its eradication (BirdLife International, 2005). Rats also preyed on a number of terrestrial invertebrates, especially the Jerusalem cricket, as well as preying on intertidal invertebrates, such as the shore crab (National Park Service, 2006).
    Hawaii (United States (USA)) English 
    Predation: Ship rats in Hawaii are thought to be responsible for suppressing seed regeneration of endemic plants, reducing populations of native snails, and significantly limiting breeding success of many native birds (Pitt, 2004). Bonin petrel (see Pterodroma hypoleuca in IUCN Red List of Threatened Species) predation can be reliably attributed to ship rats (Grant et al. 1981).



ISSG Landcare Research NBII IUCN University of Auckland