Cat predation on turtle hatchlings

Seabrook, W. 1989. Feral cats (Felis catus) as predators of hatchling green turtles (Chelonia mydas). J. Zool., Lond., 219: 83-88

In many parts of the world feral animals have been reported to have severe effects on marine turtle hatchling production. In this study, green turtle (Chelonia mydas) hatchlings were shown to be an important component of the diet of the feral cat (Felis catus) on Aldabra Atoll, Seychelles, and feral cat activity in the coastal areas was found to be concentrated on the beaches used most intensively by turtles for nesting. The impact of the feral cat's predation on green turtle recruitment could not be determined. However, despite cat predation, the size of the Aldabran green turtle nesting population has increased considerably since human exploitation ceased.

Socorro island's endemics and cats

Arnaud, G., A. Rodriguez, A. Ortega-Rubio, S. Alvarez-Cardenas. 1993. Predation by Cats on the Unique Endemic Lizard of Socorro Island (Urosaurus auriculatus), Revillagigedo, Mexico. Ohio Journal of Science, 93 (4): 101-103

During 1990 the distributions of the endemic lizard (Urosaurus auriculatus) and the feral cat (Felis catus) of Socorro Island were observed and scats of the last species were collected. A total of 46 cat scats were analyzed, showing that lizards were an important prey item, varying in frequency from 33.33% in February to 66.66% in November. Because of the impact of sheep (Ovis aries) on the natural vegetation and because of the impact of cat predation, we recommend that a plan be developed for the removal of exotic species and the restoration of natural vegetation to Socorro Island.

Jehl, J.R.& K.C. Parks. 1983. 'Replacements' of landbird species on Socorro Island, Mexico. Auk 100: 551-559.
The endemic dove Zenaida graysoni of Socorro Island, an oceanic island in the Pacific south of Baja California, became extirpated between 1958 and 1978 and the endemic mockingbird Mimodes graysoni diminished during the same years and was approaching extinction by 1981. The mainland mourning dove Z. macroura became established on Socorro between (probably) 1971 and 1978 and the mainland northern mockingbird Mimus polyglottos between 1978 and 1981. Superficially an instance of replacement of island endemics by mainland relatives through competitive exclusion, the case is actually more complicated. It is argued that extermination of the endemics was probably caused by predation by feral cats introduced in 1957 or later. There is no evidence of any actual competition between the pairs of species and their preferred habitats overlap only slightly. The nearly concurrent establishment of the 2 invading species, known to have occurred frequently as casual visitors to Socorro and other islands is attributed largely to the provision of fresh water made available as a result of human settlement. Simple comparison of island species lists compiled at intervals is an inadequate base for theories of island species turnover.

More info about Socorro's threatened birds:
BirdLife International (2013) Species factsheet: Zenaida graysoni. Downloaded from http://www.birdlife.org on 12/04/2013.
BirdLife International (2013) Species factsheet: Mimus graysoni. Downloaded from http://www.birdlife.org on 12/04/2013. 

BirdLife International (2013) Species factsheet: Aratinga brevipes. Downloaded from http://www.birdlife.orgon 12/04/2013.
BirdLife International (2013) Species factsheet: Troglodytes sissonii. Downloaded from http://www.birdlife.orgon 12/04/2013.
BirdLife International (2013) Species factsheet: Puffinus auricularis. Downloaded from http://www.birdlife.orgon 12/04/2013.

Cats' diet on some Pacific islands

Jarvis and Howlnad

R.D. Kirkpatrick and Mark J. Rauzon. 1986. Foods of Feral Cats Felis catus on Jarvis and Howland Islands, Central Pacific Ocean. Biotropica, 18 (1): 72-75

Food habits of feral cats (Felis catus) were studied on two small uninhabited islands in the central Pacific Ocean. Cat stomach contents, collected on Howland Island in May 1979 and on Jarvis Island during May 1979 and June-July 1982, revealed that sooty terns (Sterna fuscata) were the primary prey species. Other seabirds, lizards, insects and, on Jarvis Island, house mice were also eaten. Fetal cats may have virtually exterminated the wedge-tailed shearwater colony on Jarvis Island.

Kermadec
Fitzgerald, B.M.; Kark, B.J. & Veitch, C.R. 1991. The diet of feral cats (Felis catus) on Raoul Island, Kermadec Group. New Zealand Journal of Ecology 15(2): 123-129.

Feral cats became established on Raoul Island some time between 1836 and 1872; the prey available to them included a great variety of nesting seabirds, few of which are present now, landbirds and kiore (Rattus

exulans). Norway rats reached the island in 1921, providing additional prey for cats, but also another potential predator of seabirds. The diet of cats is described from guts and scats collected between 1972 and 1980. Rats are the main food, with land birds second in importance, and seabirds are now a minor item. More than 90% of the rats eaten by cats are kiore although more Norway rats than kiore are trapped. Eradicating cats from Raoul Island is feasible but because Norway rats too are important predators of birds on islands, it is likely that eradicating cats without also eradicating Norway rats will do little to restore the diversity of bird species on Raoul Island, although the densities of a few species now present might be increased.

Hawai'i
Hess, S. C.; Hansen, H.; Nelson, D.; Swift, R. & Banko, P. C. 2007. Diet of feral cats in Hawai'i Volcanoes National Park. Pacific Conservation Biology, 13: 244–249.

We documented the diet of feral cats by analysing the contents of 42 digestive tracts from Kilauea and Mauna Loa in Hawai'i Volcanoes National Park. Small mammals, invertebrates, and birds were the most common prey types consumed by feral cats. Birds occurred in 27.8-29.2% of digestive tracts. The total number of bird, small mammal, and invertebrate prey differed between Kilauea and Mauna Loa. On Mauna Loa, significantly more (89%) feral cats consumed small mammals, primarily rodents, than on Kilauea Volcano (50%). Mice (Mus musculus) were the major component of the feral cat diet on Mauna Loa, whereas Orthoptera were the major component of the diet on Kilauea. We recovered a mandible set, feathers, and bones of an endangered Hawaiian Petrel (Pterodroma sandwichensis) from a digestive tract from Mauna Loa. This specimen represents the first well-documented endangered seabird to be recovered from the digestive tract of a feral cat in Hawai'i and suggests that feral cats prey on this species.

Smucker, T. D., G. D. Lindsey, & S. M. Mosher. 2000. Home range and diet of feral cats in Hawaii forests. Pacific Conservation Biology 6: 229–237.

Feral cat Felis catus home range in a Hawaiian montane wet forest and their diet in three habitats - montane wet forest, subalpine dry forest, and lowland dry forest - were determined to provide baseline ecological data and to assess potential impacts to native terrestrial fauna. Seven cats (three males and four females) were captured in 624 trap nights. Mean weight of adult cats was 2.85 0.27 (SE) kg for males and 1.87 0.03 kg for females. Mean diurnal home range using the adaptive kernel method was 5.74 2.73 km² for three males and 2.23 0.44 km²  for two females. Daytime locations were always within the montane wet forest with the borders on one or more sides of the home ranges of all cats defined by open grassland pastures. Rodents comprised the majority of the cat diets in all three habitats, with the frequencies of occurrence between 0.88 and 0.91. Bird remains were a regular component of the diet of cats, with montane wet forest having the highest frequency of occurrence (0.68), followed by subalpine dry forest (0.53). and lowland dry forest (0.21).

Predation by domestic cat in a British village

Churcher , P.B. & J.H. Lawton. 1987. Predation by domestic cats in an English (UK) village. Journal of Zoology. (London.) 212: 439-455

We studied predation by approximately 70 domestic cats (Felis catus L.) in the Bedfordshire village of Felmersham over a one-year period. All the prey items brought home by virtually all the cats in the village were recorded and, where possible, identified. A total of 1090 prey items (53i5 mammals, 297 birds and 258 unidentified animals) were taken, an average of about 14 per cat per year. Twenty two species of birds and 15 species of mammals were identified. The most important items were woodmice (17%), house sparrows (16%) and bank voles (14%).

Old cats of both sexes caught fewer prey over the year than young cats. Female cats on the edge of the village also caught more prey than female cats in intermediate or central areas of the village; male cats showed no such effect. The type of prey caught also varied with position in the village; ‘core’ cats caught proportionately more birds than ‘edge’ cats. There was some indication in the data that cats caught fewer prey in areas where cat density was highest, but this effect was impossible to disentangle from position in the village. Weather apparently influenced hunting success. Temperature had no direct influence, but fewer prey were caught in winter; cats also caught less on wet days and windy days.

Estimates of the number of house sparrows in the village at the start of the breeding season, and the number of sparrows known to have been caught by the cats, suggest that at least 30% of the sparrow deaths in the village were due to cats. Domestic cats would appear to be major predators in this typical English village.

Trap-Neuter-Release vs. Trap-Euthanasia

Lohr, C. A., Cox, L. J. & Lepczyk, C. A. (2013), Costs and Benefits of Trap-Neuter-Release and Euthanasia for Removal of Urban Cats in Oahu, Hawaii. Conservation Biology, 27: 64–73. 

Our goal was to determine whether it is more cost-effective to control feral cat abundance with trap-neuter-release programs or trap and euthanize programs. Using STELLA 7, systems modeling software, we modeled changes over 30 years in abundance of cats in a feral colony in response to each management method and the costs and benefits associated with each method . We included costs associated with providing food, veterinary care, and microchips to the colony cats and the cost of euthanasia, wages, and trapping equipment in the model. Due to a lack of data on predation rates and disease transmission by feral cats the only benefits incorporated into the analyses were reduced predation on Wedge-tailed Shearwaters (Puffinus pacificus). When no additional domestic cats were abandoned by owners and the trap and euthanize program removed 30,000 cats in the first year, the colony was extirpated in at least 75% of model simulations within the second year. It took 30 years for trap-neuter-release to extirpate the colony. When the cat population was supplemented with 10% of the initial population size per year, the colony returned to carrying capacity within 6 years and the trap and euthanize program had to be repeated, whereas trap-neuter-release never reduced the number of cats to near zero within the 30-year time frame of the model. The abandonment of domestic cats reduced the cost effectiveness of both trap-neuter-release and trap and euthanize. Trap-neuter-release was approximately twice as expensive to implement as a trap and euthanize program. Results of sensitivity analyses suggested trap-neuter-release programs that employ volunteers are still less cost-effective than trap and euthanize programs that employ paid professionals and that trap-neuter-release was only effective when the total number of colony cats in an area was below 1000. Reducing the rate of abandonment of domestic cats appears to be a more effective solution for reducing the abundance of feral cats.


Costos y Beneficios de Captura-Esterilización-Liberación y Eutanasia para la Remoción de Gatos Urbanos en Oahu, Hawaii

Nuestra meta fue determinar si es más rentable controlar la abundancia de gatos ferales con programas de captura-esterilización-liberación o con programas de captura y eutanasia. Utilizando STELLA 7, software para modelar sistemas, modelamos cambios a lo largo de 30 años en la abundancia de gatos en una colonia feral en respuesta a cada método de manejo, así como de los costos y beneficios asociados con cada uno. En el modelo incluimos los costos asociados con la alimentación, el cuidado veterinario y los microchips para la colonia de gatos y el costo de la eutanasia, los salarios y el equipo de captura. Debido a la falta de datos sobre las tasas de depredación y de transmisión de enfermedades por gatos ferales, la reducción de la depredación sobre Puffinus pacificus fueron los únicos beneficios incorporados en el análisis. Cuando no hubo abandono adicional de gatos por sus dueños y el programa de captura y eutanasia removió 30,000 gatos en el primer año, la colonia fue extirpada en por lo menos 75% de las simulaciones del modelo en el segundo año. Tomó 30 años para que la captura-esterilización-liberación extirpara la colonia. Cuando la población de gatos fue suplementada con 10% del tamaño poblacional inicial por año, la colonia regresó a la capacidad de carga en 6 años y se tenía que repetir el programa de captura y eutanasia, mientras que la captura-esterilización-liberación nunca redujo el número de gatos a casi cero en los 30 años del marco de tiempo del modelo. El abandono de gatos domésticos redujo la rentabilidad tanto de la captura-esterilización-liberación como de la captura y eutanasia. La implementación de la captura-esterilización-liberación costó casi el doble que el programa de captura y eutanasia. Los resultados de los análisis de sensibilidad sugirieron que los programas de captura-esterilización-liberación que emplean voluntarios son aun menos rentables que los programas de captura y eutanasia que emplean profesionales pagados y que la captura-esterilización-liberación solo fue efectiva cuando el número total de gatos en un área era menor a 1000. La reducción de la tasa de abandono de gatos domésticos parece ser una solución más efectiva para reducir la abundancia de gatos ferales.

Cat diet on several sub-Antarctic islands

Kerguelen
Pontier, D., L. Say, F. Debias, J. Bried, J. Thioulouse, T. Micol & E. Natoli. 2002. The diet of feral cats (Felis catus L.) at five sites on the Grande Terre, Kerguelen archipelago. Polar Biology, 25: 833–837
Assessing the impact (direct or indirect) of introduced predator species on native seabird populations is a clear management priority, particularly so in the simple sub-Antarctic ecosystems where these effects may be dramatic. We evaluated the diet of introduced feral cats (Felis catus L.) on the Grande Terre, Kerguelen archipelago, by analysing 149 scats from 5 sites. Overall, rabbits (Oryctolagus cuniculus) were the primary prey (72.6%), followed by house mice (Mus musculus) (11.6%) and birds (all species confounded, 14.9%). However, the proportions of the three prey species varied among sites, reflecting the spreading pattern of cats onto the Grande Terre. Birds were consumed much less frequently in this study (7.3%, all sites pooled but one) compared to a 1976 study in the same area (66.3%), suggesting that cats had a strong impact on the native avifauna

Marion
van Aarde, R.J. 1980. The diet and feeding behaviour of feral cats, Felis catus at Marion Island. South African Journal of Wildlife Research, 10:123-128.

Analyses of prey remains (n = 1 224) and stomach contents (n = 125) of feral domestic cats at Marion Island indicated that these exotic predators mainly feed on nocturnal burrow­ing petrels (fam. Procellariidae). Seasonality in their diet is discussed and predation rate on the various prey species seems to be a factor of availability rather than selection. An estimate of predation rate based on the energy requirements of the cat population and the caloric content of their most im­portant prey species suggested that a single cat kills approximately 213 petrels per year.

Auckland
Harper, G.A. 2010. Diet of feral cats on subantarctic Auckland Island. New Zealand Journal of Ecology, 34(2): 259-261
Feral cats were trapped and cat scats collected at Port Ross, Auckland Island, during two weeks in winter 2007. Eleven cats were caught and 40 scats collected, including from upland tussock areas. Cats’ diet predominantly consisted of birds (77.5% occurrence in scats) and mice (52.5% occurrence). The cats were relatively heavy and in good condition compared with other feral cats in New Zealand populations.

Macquarie
Jones, E. (1984). The feral cat on Macquarie Island. Tasmanian Naturalist, 79: 16-17

Domestic cats must have been taken to Macquarie Island soon after its discovery in 1810; feral cats were reported on the Island by 1820 (Debenham 1945). No records are available on the activities of these cats for the next 70 years, but the role of the feral cat as a predator of burrow-nesting petrels was then recognised by visitors to Macquarie Island such as Hamilton (1894), Burton (1900) and Mawson (1916) (the latter two in Cumpston 1968).
During 1974 I studied the diet of feral cats on Macquarie Island by a combination of scat and gut analysis, in an effort to determine their present ecological impact on the Island's fauna.

The percentage frequencies of the major food items found in 756 cat scats are presented in Table 1.

TABLE 1. Occurrence of major food items in 756 cat scats.

Food Item	Number of Seats	Percentage Frequency
Rabbit	619	81.9
Prion	220	29.1
White-headed Petrel	120	15.9
Mouse	33	4.4
Penguin	25	3.3
Rat	20	2.6
Weka	15	2.0

These results clearty indicate that rabbits, Antarctic Prions and White-headed Petrels were the major dietary items; other foods were less frequently eaten. The analysis of the gut contents of an additional 41 adult cats confirmed this finding but also indicated a seasonal change of diet during winter when less common food items such as wekas were eaten, and scavenging on dead elephant seals and penguins took place. Also, by the measurement of bone fragments it was found that 58% of the rabbits eaten weighed 200 - 300g, 23% weighed 300 - 600g, 8% weighed 600 - 1300g, and 11% weighed more than 1300g.

Cats were sighted and seats collected from all parts of the Island but densities were highest in areas of greatest prey abundance. It was estimated that in 1974 there were between 250 - 500 adult cats present and those cats collected were similar in size (mean weight of males 4518g; mean weight of females 2844g) to common domestic cats.

The ecological impact that these cats are now having on the fauna of Macquarie Island is difficult to assess, due to the other major ecological changes which have also taken place. However thei r depredations may still be affecting the less common species of petrels present.

Since most burrow-nesting petrels are absent from the Island during winter and the young rabbits have grown larger, the total amount of food available to the cats at this time is at a minimum. This winter food stress acts as a yearly limit to the cat population size and also causes the change in diet mentioned earlier. Thus if a major reduction in the rabbit population could be achieved, then this would cause a corresponding reduction in the cat population. The remaining cats would then become major predators of young rabbits in the following spring and summer and suppress the rate of increase of the rabbit population. However if rabbits were eliminated from Macquarie Island, feral cats would become rare.

More on Macquarie island cats

Campbell

Dilks, P.J. Observations on the food of feral cats on Campbell Island. New Zealand Journal of Ecology, 2: 64-66. 

Feral cats (Felis catus) are very scarce on Campbell Island (52 S, 169 E). Scats were collected during three summer visits and later examined. Norway rats (Rattus norvegicus) were much the most important prey, although birds and insects were also taken.

Toxoplasmosis affecting endangered native Hawaiian bird

Work,T.M.,  J. G. Massey, B.A. Rideout, C.H. Gardiner, D. B. Ledig, O. C. H. Kwok & J. P. Dubey. 2000. Fatal toxoplasmosis in free-ranging endangered 'Alala from Hawaii. Journal of Wildlife Diseases, 36(2): 205–212

The ‘Alala (Corvus hawaiiensis) is the most endangered corvid in the world, and intensive efforts are being made to reintroduce it to its former native range in Hawaii. We diagnosed Toxoplasma gondii infection in five free-ranging ‘Alala. One ‘Alala, recaptured from the wild because it was underweight and depressed, was treated with diclazuril (10 mg/kg) orally for 10 days. Antibodies were measured before and after treatment by the modified agglutination test (MAT) using whole T. gondii tachyzoites fixed in formalin and mercaptoethanol. The MAT titer decreased four-fold from an initial titer of 1:1,600 with remarkable improvement in physical condition. Lesions of toxoplasmosis also were seen in two partially scavenged carcasses and in a third fresh intact carcass. Toxoplasma gondii was confirmed immunohistochemically by using anti-T. gondii specific serum. The organism was also cultured by bioassay in mice from tissues of one of these birds and the brain of a fifth ‘Alala that did not exhibit lesions. The life cycle of the parasite was experimentally completed in cats. This is the first record of toxoplasmosis in ‘Alala, and the parasite appears to pose a significant threat and management challenge to reintroduction programs for ‘Alala in Hawaii.

What conservation biologists can do to counter TNR

Lepczyk, C., Dauphine, N., Bird, D., Conant, S., Cooper, R., Duffy, D., Hatley, P.J., Marra, P.P., Stone, E. & Temple, S. (2010). What conservation biologists can do to counter trap-neuter-return: response to Longcore et al. Conservation Biology: 24(2), 627.

Suggestions:

1-     Conservation biologists, wildlife ecologists and the like should have open dialogues with the animal welfare, sheltering, veterinary and public-health communities

2-     The wildlife and conservation communities need to challenge policies that are put forth to allow or promote feral cat colonies and TNR.

3-     The wildlife and conservation communities should advocate for policies that encourage responsible pet ownership as well as for enforcement of existing policies.

4-     Releasing cats into the wild and supporting feral cat colonies is a violation of the Migratory Bird Treaty Act and the Endangered Species Act, as well as laws prohibiting animal abandonment.

5-     We should seek laws making it illegal to maintain cat colonies on public lands

6-     We need to increase public awareness about being a responsible pet owner not just for the benefit of cats but also for individuals of wildlife species and the environment

7-     We need to move away from the prevailing view that depredation of individual species does not matter as long as their populations are intact. If we consirde cats from an individualistic viewpoint, then the same argument must be made for wild animals.

See also here

Critical assessment of TNR

Longcore, T, C. Rich & L. M. Sullivan. 2009. Critical assessment of claims regarding  management of feral cats by Trap-Neuter-Return. Conservation Biology 23:887–894.


Many jurisdictions have adopted programs to manage feral cats by trap–neuter–return (TNR), in which cats are trapped and sterilized, then returned to the environment to be fed and cared for by volunteer caretakers. Most conservation biologists probably do not realize the extent and growth of this practice and that the goal of some leading TNR advocates is that cats ultimately be recognized and treated as “protected wildlife.” We compared the arguments put forth in support of TNR by many feral cat advocates with the scientific literature. Advocates promoting TNR often claim that feral cats harm wildlife only on islands and not on continents; fill a natural or realized niche; do not contribute to the decline of native species; and are insignificant vectors or reservoirs of disease. Advocates also frequently make claims about the effectiveness of TNR, including claims that colonies of feral cats are eventually eliminated by TNR and that managed colonies resist invasion by other cats. The scientific literature contradicts each of these claims. TNR of feral cats is primarily viewed and regulated as an animal welfare issue, but it should be seen as an environmental issue, and decisions to implement it should receive formal environmental assessment. Conservation scientists have a role to play by conducting additional research on the effects of feral cats on wildlife and by communicating sound scientific information about this problem to policy makers.



Muchas jurisdicciones han adoptado programas para el manejo de gatos ferales mediante la captura– esterilización– liberación (CEL), en los que los gatos son atrapados y esterilizados y devueltos al ambiente para ser alimentados y cuidados por voluntarios. La mayoría de los biólogos de la conservación probablemente no comprenden la extensión y crecimiento de esta práctica y que la meta de los defensores de CEL es que los gatos sean reconocidos y tratados como “vida silvestre protegida”. Comparamos los argumentos en apoyo a CEL por muchos defensores de gatos ferales con la literatura científica  Los defensores que promueven el CEL sostienen que los gatos ferales solo dañan a la vida silvestre en islas y no en los continentes; ocupan un nicho natural o realizado; no contribuyen a la declinación de especies nativas y son vectores o reservorios de enfermedad insignificantes. Los defensores frecuentemente también sostienen que la efectividad de CEL, incluyendo argumentos que las colonias de gatos ferales eventualmente son eliminadas por CEL y que las colonias manejadas resisten la invasión de otros gatos. La literatura científica contradice cada uno de esos argumentos. CEL de gatos ferales es vista y regulada principalmente como un asunto de bienestar animal, pero debería verse como un tema ambiental, y las decisiones para su implementación deberían recibir una evaluación ambiental formal. Los científicos de la conservación tienen un papel importante al realizar investigaciones adicionales sobre los efectos de los gatos ferales sobre la vida silvestre y en la comunicación de información científica solida a los tomadores de decisiones.

Prey of domestic cats in Auckland

 Gillies, C. & M. Clout (2003). The prey of domestic cats (Felis catus) in two suburbs of Auckland City, New Zealand. Journal of Zoology, 259: 309-315.

The prey brought in by 80 cats Felis catus over 1 year was monitored in two suburbs of Auckland, New Zealand: one suburb was completely urban, the other on the urban/forest fringe. Cat owners were asked to record and, if possible, keep the prey that their cats brought in. Rodents were the main prey brought in by domestic cats in the urban/forest fringe habitat, whereas invertebrates were the main prey in the fully urban habitat. Birds were caught in similar numbers by cats in both areas and were the second most important prey group at both study sites. However, more native birds were caught by cats in the urban/forest fringe area than in the fully urban habitat. Lizards were caught in similar numbers and were the third most important prey group in both study areas.

Impact of domestic cats in an urban area

Baker, P. J., A. J. Bentley, R. J. Ansell, & S. Harris. 2005. Impact of predation by domestic cats Felis catus in an urban area. Mammal Review 35:302–312.

As companion animals, domestic cats Felis catus can attain very high densities, and have the potential to exert detrimental effects on prey species. Yet, there is a paucity of information on the impact of cat predation in urban areas, where most cats are likely to be present.

We quantified the minimum number of animals killed annually by cats in a 4.2-km2 area of Bristol, UK, by asking owners to record prey animals returned home by their pets. The potential impact of cat predation on prey species was estimated by comparing the number of animals killed with published estimates of prey density and annual productivity.

Predator density was 229 cats/km2.

Five mammal, 10 bird and one amphibian prey species were recorded. Mean predation rate was 21 prey/cat/annum. The most commonly recorded prey species was the wood mouse Apodemus sylvaticus.

Predation on birds was greatest in spring and summer, and probably reflected the killing of juvenile individuals. For three prey species (house sparrow Passer domesticus, dunnock Prunella modularis, robin Erithacus rubecula), estimated predation rates were high relative to annual productivity, such that predation by cats may have created a dispersal sink for juveniles from more productive neighbouring areas. The impact of cats on these species therefore warrants further investigation.

American Society of Mammalogists' position on TNR

Position of the American Society of Mammalogists on Trap-Neuter-Release (Return) of Feral Cats—approved June 2010

Trap–Neuter–Release (TNR) programs in which feral cats (Felis catus) are sterilized and then released back into the environment have been proposed as a non-lethal alternative to control feral populations of this predator and to lessen their environmental impact. TNR programs have been adopted or tacitly allowed by a number of metropolitan areas in the US, despite lack of evidence of their efficacy and despite accumulation of data confirming the negative effect of free-ranging cats on birds and mammals.
As mesocarnivores, domestic cats commonly prey upon native vertebrates, including mammals. Whereas predators are normally in low abundance in natural communities, feral populations of cats are frequently maintained at high levels through recruitment from human-maintained sources and through food subsidies. Although feeding feral cats lessens their dependence on predation, it does not necessarily lessen their frequency of predation.
Cats have been implicated in population decreases of mammals, birds, and reptiles on islands, as well as in mainland communities. Further, fragmentation of natural environments through agriculture and urbanization results in mammalian assemblages that more closely resemble insular than continental communities, which magnifies the impact of subsidized predators on natural populations. In addition to their direct impact through predation, feral cats are sources of parasites and diseases transmissible to humans, livestock, pets, and native populations.
It is the position of the American Society of Mammalogists that maintenance of high populations of these non-native predators through TNR or similar programs, or by subsidizing feral populations with supplemental food, is extremely detrimental to native mammalian assemblages. The American Society of Mammalogists strongly opposes TNR and urges municipalities to ban use of such programs and to prohibit feeding of feral cats. We further encourage effective measures to reduce or eliminate feral populations of these introduced predators.

Cats, birds and you: A brochure from ABC

You can download the pdf here.

Feral cats' diet in Australia

Another pair of articles and a review on cats' diet in Australia.

Paltridge, R., D. Gibson & G. Edwards. 1997. Diet of the Feral Cat (Felis catus) in Central Australia. Wildlife Research 24(1) 67 - 76

Feral cats (Felis catus) occur throughout central Australia. In this study, we analysed the stomach contents of 390 feral cats collected between 1990 and 1994 from the southern half of the Northern Territory. Cats fed on a wide variety of invertebrates, reptiles, birds and mammals, including animals up to their own body mass in size. Mammals were the most important prey but reptiles were regularly eaten in summer and birds were important in winter. Invertebrates were present in the diet in all seasons. Carrion appeared in stomach samples during dry winters only and this has implications for future control of feral cats.

Martin, G.R., L.E. Twigg & DJ Robinson. 1996. Comparison of the Diet of Feral Cats From Rural and Pastoral Western Australia. Wildlife Research 23(4): 475 - 484

The stomach contents of 93 cats from rural and pastoral Western Australia were compared using the number and biomass of food items, and by calculating an Index of Relative Importance for each food category. Species of small native mammals (e.g. dasyurids, rodents) and geckos were significantly (P < 0.03) more prevalent in the diet of pastoral cats, and rural cats consumed greater (P < 0.03) quantities of introduced rodents and rabbits. Several other groups of native animals (e.g. snakes, skinks, agamids) were also more prevalent in the stomachs of pastoral cats (P < 0.10). Birds and orthopterans were important food items to cats from both habitats. There was reasonable dietary overlap (mean = 0.71) between the cats from both habitats, but the dietary breadth of the pastoral cats (mean = 0.44) was two-fold greater than that of the rural cats (mean = 0.21). These findings are compared with previous studies, and are discussed with respect to possible implications for future management strategies for feral cats.

Major prey of prey of feral cats in Australia (from Dickman, C. R. 1996)

Data collected from 22 studies of feral cats in mainland Australia suggest that mammals comprise the major prey of feral cats in most localities. Introduced rabbits (Oryctolagus cuniculus) and house mice (Mus domesticus) predominate in semi-arid to arid habitats, whereas marsupials (especially the common ringtail possom (Pseudocheirus peregrinus) are predominant in temperate forest, urban and suburban habitats (Dickman 1996). Brushtail possoms (Trichosurus vulpecula), sugar gliders (Petaurus breviceps), greater gliders (Petauroides volans) and smaller prey such as brown antechinus (Antechinus stuartii), brush rat (Rattus fuscipes) and swamp rat (Rattus lutreolus) are consistently part of the diet of feral cats in the temperate forests of Australia. In wet-dry tropical habitats where rabbits do not occur native Rattus spp. become more important, including the pale field rat (Rattus tunneyi), dusky rat (R. colletti) and the long-haired rat (Rattus villosissimus).
Smaller rodents such as the spinifex hopping mouse (Notomys alexis) and the sandy inland mouse (Pseudomys hermannburgensis) may also be preyed upon. Birds are represented most highly in
temperate forest, urban and suburban habitats. Small species such as wrens (Malurus spp.), robins (Petroica spp.) and thornbills (Acanthiza spp.) have all been recorded, as have larger species such as galahs (Cacatua roseicapilla), magpies (Gymnorhina tibicen) species of parrots (Psephotus spp.). Species such as geckos and flap-footed lizards and diurnal species of skinks, dragons, goannas and snakes have often been recorded in the feral cat's diet (Dickman 1996).
Reviews of the diet of feral cats in mainland areas in other parts of the world reveal great similarities with the situation in Australia (Corbett, 1979, Fitzgerald and Karl 1979, Liberg 1984, Fitzgerald 1988, Kitchener 1991, in Dickman 1996). In all studies, mammals have consistently comprised the major part of the diet throughout the year, with other vertebrates, especially birds, comprising only a minor component. Rabbits
and murid rodents, especially Rattus species, appear to be favoured prey, and together comprise the bulk of the diet of feral cats in some localities over long periods.

Subsidies influence on feral cat distribution and abundance

Tennent, J. & C.T. Downs. 2008. Abundance and home ranges of feral cats in an urban conservancy where there is supplemental feeding: a case study from South Africa. African Zoology 43(2):218-229.


There is much debate surrounding the impact of feral cats (Felis catus) on wildlife. Conservancies are usually areas where indigenous flora and fauna are protected and aliens excluded or managed. The University of KwaZulu-Natal's Howard College campus (HCC) is an urban conservancy containing feral cats that are presently not managed, and little is known about their ecology and behaviour. Consequently a feral cat population census was conducted, and their home range investigated. Estimates of the overall campus feral cat population numbers ranged between 23.4–40.0 cats/km² with a minimum of 55 identified as resident. They were not randomly distributed in the study area, with spacing patterns being related to resource availability. Home range area and core distribution of eight radio-collared cats were determined over 13 months. Total home range areas were relatively small, with considerable overlap between them. Home ranges were clustered in areas with permanent feeding stations and these were also within the cats' core ranges. Supplemental food resources appear to have a major influence on numbers, home and core range area, and behavior of cats. It is clear that cat densities grow to high levels with reliable and abundant food supply and only ad hoc sterilization. This has implications for their management in the HCC urban conservancy.