General Impact
The most obvious impact of feral cats is the predatory impact they exert on native prey populations; this has resulted in the probable local or regional decline or extinction of many species (Dickman 1996). However, unambiguous evidence of cats causing a decline in a prey species is difficult to find as other factors, such as other predator species, may also be involved in the decline (Dickman 1996). One exception to this is a study by Saunders (1991) which showed that cats killed 7% of nestlings of red-tailed cockatoos (Calyptorhynchus magnificus) over 11 breeding seasons in Western Australia. Several reintroduction programmes in Australia have failed, due to the predation pressure exerted by feral cats, often in conjunction with foxes. For example, the success of the reintroductions of the golden bandicoot (Isoodon auratus) and the burrowing bettong (Bettongia lesueur) in the Gibson Desert, Western Australia was hindered primarily by feral cat predation. In general, the predatory impact of cats primarily affects birds and small to medium-sized mammals (Dickman 1996). Endangered species around the world are threatened by the presence of cats, including the black stilt (see Himantopus novaezelandiae in the IUCN Red List of Threatened Species) (New Zealand), the Okinawa woodpecker (see Sapheopipo noguchii in IUCN Red List of Threatened Species) (Japan) and the Cayman Island ground iguana (see Cyclura lewisi in IUCN Red List of Threatened Species), to list just some of the many species effected.
Changes in island fauna after the introduction of cats can provide compelling evidence of their predatory impact. Cats have been introduced to 40 islands off the coast of Australia; seven off the coast of New Zealand and several dozen islands elsewhere in the Pacific (Dickman 1992a, Veitch 1985, King 1973 1984, in Dickman 1996). Feral cats have been implicated in the decline of at least six species of island endemic birds in New Zealand, including the Stephens Island wren, the sooty shearwater (Puffinus griseus) and the kakapo (Strigops habroptilus), as well as 70 local populations of insular birds (King 1984, in Dickman 1996). The elimination of cats often leads to an increase in the population size of prey species. For example, following removal of cats from Little Barrier Island, New Zealand, the stitchbird (Notiomystis cincta) increased from less than 500 individuals to 3000 individuals in just a few years (Griffin et al. 1988, in Dickman 1996).
Location Specific Impacts:Macquarie Is. (sub-Antarctic) (Australia) 
Other: Depredations by cats greatly reduced the numbers of burrow-nesting petrels on the island and, together with the weka Gallirallus australis, cats were probably responsible for the extinction of the endemic red-fronted parakeet (see Cyanoramphus novaezelandiae in IUCN Red List of Threatened Species) and banded rail Rallus phillippensis before 1900. Cat numbers on subantarctic islands fluctuate seasonally according to fluctuations in the abundance and availability of prey (rabbits and burrow-nesting petrels). When rabbits are absent, winter-breeding burrow-nesting petrels sustain cats through winter, taking the brunt of cat predation (Brothers et al.. 1985). Dirk Hartog Is. (Australia)
Other: Although Dirk Hartog Island remains a pastoral station and has also supported large populations of goats (Burbidge and George 1978, in Dickman 1996), strong comparative evidence implicates cats in the wave of extinctions. Bernier and Dorre Islands, to the north of Dirk Hartog, do not have cats and have retained their original faunas almost intact. Both Bernier and Dorre have been subject, to intermittent human occupation and sheep grazing; goats were also present on Bernier for nearly 90 years and caused considerable damage to the island's vegetation before their eradication in the mid-1980s (Morris, 1989, in Dickman 1996).
Reduction in native biodiversity: Cats have been implicated in the loss of several small and medium-sized mammals from Dirk Hartog Island, Western Australia. Burbidge & George (1978) report local knowledge that the `wallabies' (see Lagostrophus fasciatus in the IUCN Red List of Threatened Species) and the burrowing bettong (see Bettongia lesueur in the IUCN Red List of Threatened Species) became extinct in the 1920s. However, as some doubt has been cast recently on the former presence of L. fasciatus on Dirk Hartog (Baynes 1990, in Dickman 1996) the local reports may refer to B. lesueur alone. The following species also went extinct on the island probably in part due to predation by feral cats: the mulgara (see Dasycercus cristicauda in the IUCN Red List of Threatened Species), the Western quoll (see Dasyurus geoffroii in the IUCN Red List of Threatened Species), Sminthopsis dolichura (the little long-tailed dunnart), the Western barred bandicoot (see Perameles bougainville in the IUCN Red List of Threatened Species), Pseudomys albocinereus (the ash-grey mouse) and Pseudomys hermannsburgensis (the sandy inland mouse). Long Cay (Bahamas)
Reduction in native biodiversity: Felis catus contributed to extirpation of iguanas from Pine Cay and others, and also known to predate other native reptile and bird species (Iverson, 1978 in Varnham, 2006; Gerber, 1995 in Varnham, 2006).
Threat to endangered species: Felis catus predates on the native 'Critically Endangered (CR)' Turks & Caicos rock iguana (see Cyclura carinata in IUCN Red List of Threatened Species) (Mitchell et al., 2002 in Varnham, 2006). Bermuda
Predation: Cats prey on bird life and kill native tropical birds in Bermuda (Varnham 2006). Bermuda
Reduction in native biodiversity: Cats, Felis catus prey on bird life (De Silva, 2003 in Varnham, 2006), they are known to kill native tropicbirds (Dobson, 2002 in Varnham, 2006). Falkland Islands (Malvinas) (sub-Antarctic)
Reduction in native biodiversity: Felis catus have major impact on the distribution of ground nesting birds.
Threat to endangered species: Felis catus may have lead to much reduced populations of some vulnerable species. Breeding of the Tussock bird (Cinclodes antarcticus antarcticus) and the 'Vulnerable (VU)' Cobb's wren (see Troglodytes cobbi in IUCN Red List of Threatened Species) have become restricted to cat- and rat-free islands due to predatory impacts (in Atkinson, 1985 in Varnham, 2006). Feral cats and rats are likely to have decimated entire populations of Cobb's wren on some small islands (BirdLife International 2006). Nanuyalevu Is. (Turtle Is.) (Fiji)
Reduction in native biodiversity: A survey reports that the presence of a large number of feral cats is why the banded rail (Gallirallus philippensis) and other ground-nesting birds have been eradicated, or nearly so. Feral cats have also been reported as being the likely cause for the rather low density of ground skinks. Society Islands (French Polynesia (Polynésie Française))
Reduction in native biodiversity: Introduced by Europeans, feral cats contributed to the extinction of many species and they may be the direct cause of extirpation of ground doves Gallicolumba spp. On many islands. French Polynesia (Polynésie Française) 
Reduction in native biodiversity: There have been few detailed studies of the impact of cats on these islands. However, cats are suspected of having contributed to the extinction of many bird species and to be one of the main causes of declining populations of ground-dwelling doves (Gallicolumba sp.). Amsterdam Is. (sub-Antarctic) (French Southern Territories)
Reduction in native biodiversity: Observed for the first time in 1931, cats have certainly contributed to the extinction or depletion of several species of birds. The avifauna originally consisted of nearly 20 species (Decante et al., 1987), but only 8 remain today (H, Weimerskirch in Chapuis et al., 1994). Juan de Nova Is. (French Southern Territories)
Threat to endangered species: A recent study has highlighted the pervasiveness of these mammals on the island of Juan de Nova and the strong impact they have on populations of seabirds including terns (Faulquier, 2005). For example, dozens of fresh corpses of adults were found over an area of less than one hectare in one afternoon. Amongst the tern species, the population of swift tern (see Sterna bergii in the IUCN Red List of Threatened Species), which is estimated at 250 pairs on the island of Juan de Nova, is perhaps the most vulnerable. Even minimal predation by cats could lead to their rapid decline and even extinction. Kerguelen Is. (sub-Antarctic) (French Southern Territories)
Reduction in native biodiversity: It is reported that during the 1970s feral cats killed as many as 1.2 million sea birds a year (Nogales et al. 2004). Mexico
Reduction in native biodiversity: It is reported that in northwestern Mexico, on the islands of Baja, California, cats have caused rodent extinctions with over 10 taxa extinct or nearly extinct (Nogales et al. 2004). Socorro (Mexico)
Threat to endangered species: Feral cats were introduced to Socorro in the early 1970's and have been implicated in reducing the critically endangered Townsend's shearwater (Puffinus auricularis in IUCN Redlist of Threatened Species) numbers. More than 92% of cat scats above 500m have been reported to contain shearwater remains. P. auricularis has been extirpated from two islands (Clarion and San Benedicto), and breeding is now restricted to an extremely small area on one island. Sheep (Ovis aries) are also a threat to nesting habitats through grazing (BirdLife International 2006). Coronados Is. (Mexico)
Reduction in native biodiversity: It is reported that on Coronados Islands, Cassin's auklets (Ptychoramphus aleuticus) were driven to extinction due to cat predation, but recolonised the island within 4 years after cats were eradicated (Nogales et al. 2004). Montserrat
Reduction in native biodiversity: Felis catus are likely to also eat other birds, herptiles and rats (Hilton, 2004 in Varnham, 2006).
Threat to endangered species: Signs of cat predation on adult 'Vulnerable (VU)' forest thrushes (seee Cichlherminia lherminieri in IUCN Red List of Threatened Species) and bridled quail-dove (Geotrygon mystacea) (restricted-range species) have been noted (Hilton, 2004 in Varnham, 2006). Grand Terre Is. (New Caledonia) (New Caledonia (Nouvelle Calédonie))
Reduction in native biodiversity: Examination of cat excrement collected in Grande-Terre has produced the remains of rodents and some birds and reptiles (Rouys and Theuerkauf, 2003). Cats have a high predation toll on the localised and threatened colonies of Procellariidae, particularly on colonies of Gould's petrel (see Pterodroma leucoptera in IUCN Red List of Threatened Species). Wild populations of cats are likely to cause serious disruption to populations of birds and endemic reptile fauna (Pascal et al., 2006). New Zealand
Reduction in native biodiversity: Feral cats have been implicated in the decline of at least six species of island endemic birds in New Zealand as well as 70 local populations of insular birds (King 1984, in Dickman 1996). The species include the Stephens Island wren, sooty shearwaters (Puffinus griseus) and the kakapo (Strigops habroptilus). Stewart Is. (New Zealand)
Reduction in native biodiversity: At least five species of bird have disappeared from the island, in part due to the predatory impact of cats: the South Island kokako (Caiiaeas cinerea cinerea), Stead's bush wren (see Xenicus longipes in the IUCN Red List of Threatened Species), the Stewart Island snipe (Coenocorypha aucklandica iredalei), the South Island saddleback (see Philesturnus carunculatus in the IUCN Red List of Threatened Species) and the yellowhead (Mohoua orchrocephala). A sixth species, the brown teal (Anas aucklandica chlorotis), has not been seen since 1972. A seventh species, the kakapo (Strigops habroptilus), was rediscovered in 1977 in a small area of about 10 000ha(King, 1984). Kakapo are an unimportant component of the diet of feral cats and occur in only -5% of cat scats. However, the impact on kakapo is severe. Between 1980 and 1982 about 60% of male birds were killed by cats. Between the 1981-82 season and late 1983 the population was estimated to have declined from 50-150 to just 20 birds (King 1984, in Dickman 1996). Cats also prey on parakeets (Cyanoramphus spp.), pipits (Anthus novaeseelandiae), blue penguins (Eudyptes minor) and Fiorldland crested penguins (see Eudyptes pachyrhynchus in the IUCN Red List of Threatened Species).
Threat to endangered species: A continuing decline in population size of the New Zealand dotterel (see Charadrius obscurus in the IUCN Red List of Threatened Species) on Stewart Island has also been attributed to predation from feral cats; the island population now numbers only 60-65 birds and is considered endangered (Dowding and Murphy 1993 in Dickman 1996). Reunion (La Réunion)
Threat to endangered species: There have been few detailed studies on the local impact of the wild cat. However, examination of its diet at Piton des Neiges shows that it exerts strong predation on localised and threatened colonies of Procellariidae, particularly on colonies of endangered Barau's petrel (see Pterodroma baraui in the IUCN Red List of Threatened Species) (Faulquier, 2005). Ascension Is. (Saint Helena)
Threat to endangered species: Feral cats are held responsible for the systematic predation of turtle hatchings (George and White, 2003 in Varnham, 2006). They are also implicated in decline of many ground nesting seabird species which are now restricted to cat-free offshore stacks and islets (George and White, 2003 in Varnham, 2006). Saint Helena
Reduction in native biodiversity: Felis catus are known to predate seabirds on the island. They are believed to be largely responsible for the demise of St Helena's historic seabird colonies (Ashmole and Ashmole, 2000 in Varnham, 2006). Samoa
Predation: Cats “have become wild in great numbers, and prove most destructive to many kinds of birds” (Stair 1897). Pine Cay (Turks and Caicos Islands)
Reduction in native biodiversity: Felis catus contributed to extirpation of iguanas from Pine Cay and others, and also known to predate other native reptile and bird species (Iverson, 1978 in Varnham, 2006; Gerber, 1995 in Varnham, 2006).
Threat to endangered species: Felis catus predates on the native 'Critically Endangered (CR)' Turks & Caicos rock iguana (see Cyclura carinata in IUCN Red List of Threatened Species) (Mitchell et al., 2002 in Varnham, 2006). Turks and Caicos Islands
Threat to endangered species: Cats prey on the Turks and Caicos rock iguana (see Cyclura carinata in the IUCN Red List of Threatened Species) (Varnham 2006). Iverson (1978, 1979, in Gerber and Iverson Undated) documented the near-extirpation of a population of over 5,000 adult iguanas from Pine Cay (3.9km2) in just three years as a result of predation by feral cats and dogs. In 1995, iguanas were found on only five of 26 islands with cats or livestock (G. Gerber and M. Welch, Unpub. Data, in Gerber and Iverson Undated). Cats on the islands also prey on native reptiles and birds (Varnham 2006). Turks and Caicos Islands
Reduction in native biodiversity: Felis catus contributed to extirpation of iguanas from Pine Cay and others, and also known to predate other native reptile and bird species (Iverson, 1978 in Varnham, 2006; Gerber, 1995 in Varnham, 2006).
Threat to endangered species: Felis catus predates on the native 'Critically Endangered (CR)' Turks & Caicos rock iguana (see Cyclura carinata in IUCN Red List of Threatened Species) (Mitchell et al., 2002 in Varnham, 2006). Haleakala National Park (United States (USA))
Threat to endangered species: Predation by feral cats has been identified as the most serious threat to the decline in populations of the colonies of the endangered Hawaiian petrel (see Pterodroma sandwichensis in IUCN Red List of Threatened Species) on the Hawaiian islands. Colonies of petrels have been recorded on Maui in the Haleakala National Park, Mauna Kea, Mauna Loa, Kaua`I, Lana`I and small numbers on Moloka`I (BirdLife International 2006). Kaua`i Is. (United States (USA))
Threat to endangered species: Predation by feral cats has been identified as the most serious threat to the decline in populations of the colonies of the endangered Hawaiian petrel (see Pterodroma sandwichensis in IUCN Red List of Threatened Species) on the Hawaiian islands. Colonies of petrels have been recorded on Maui in the Haleakala National Park, Mauna Kea, Mauna Loa, Kaua`I, Lana`I and small numbers on Moloka`I (BirdLife International 2006). Lana`i (Lanai) Is. (United States (USA))
Threat to endangered species: Predation by feral cats has been identified as the most serious threat to the decline in populations of the colonies of the endangered Hawaiian petrel (see Pterodroma sandwichensis in IUCN Red List of Threatened Species) on the Hawaiian islands. Colonies of petrels have been recorded on Maui in the Haleakala National Park, Mauna Kea, Mauna Loa, Kaua`I, Lana`I and small numbers on Moloka`I (BirdLife International 2006). Mauna Loa (United States (USA))
Threat to endangered species: Predation by feral cats has been identified as the most serious threat to the decline in populations of the colonies of the endangered Hawaiian petrel (see Pterodroma sandwichensis in IUCN Red List of Threatened Species) on the Hawaiian islands. Colonies of petrels have been recorded on Maui in the Haleakala National Park, Mauna Kea, Mauna Loa, Kaua`I, Lana`I and small numbers on Moloka`I (BirdLife International 2006).
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