How many feral cats are in Australia?

Legge, S., Murphy, B. P., McGregor, H., Woinarski, J. C. Z., Augusteyn, J., Ballard, G., ... & Edwards, G. (2016). Enumerating a continental-scale threat: How many feral cats are in Australia?. Biological Conservation.

Feral cats (Felis catus) have devastated wildlife globally. In Australia, feral cats are implicated in most recent mammal extinctions and continue to threaten native species. Cat control is a high-profile priority for Australian policy, research and management. To develop the evidence-base to support this priority, we first review information on cat presence/absence on Australian islands and mainland cat-proof exclosures, finding that cats occur across >99.8% of Australia's land area. Next, we collate 91 site-based feral cat density estimates in Australia and examine the influence of environmental and geographic influences on density. We extrapolate from this analysis to estimate that the feral cat population in natural environments fluctuates between 1.4 million (95% confidence interval: 1.0–2.3 million) after continent-wide droughts, to 5.6 million (95% CI: 2.5–11 million) after extensive wet periods. We estimate another 0.7 million feral cats occur in Australia's highly modified environments (urban areas, rubbish dumps, intensive farms). Feral cat densities are higher on small islands than the mainland, but similar inside and outside conservation land. Mainland cats reach highest densities in arid/semi-arid areas after wet periods. Regional variation in cat densities corresponds closely with attrition rates for native mammal fauna. The overall population estimate for Australia's feral cats (in natural and highly modified environments), fluctuating between 2.1 and 6.3 million, is lower than previous estimates, and Australian feral cat densities are lower than reported for North America and Europe. Nevertheless, cats inflict severe impacts on Australian fauna, reflecting the sensitivity of Australia's native species to cats and reinforcing that policy, research and management to reduce their impacts is critical.

The population size of feral cats in natural environments in Australia fluctuates between 1.4 and 5.6 million, depending on rainfall. An additional 0.7 million feral cats live in heavily modified environments like towns and intensive farms. The maps show the model predictions for cat density in natural environments across Australia during dry-average rainfall conditions (on the left) and after extensive rainfall events (on the right). They show that cat density is fairly uniform across the continent during average-dry conditions, but extensive rainfall events cause an increase in feral cat density in the inland of Australia. As predictors, the regression model includes mean annual rainfall, mean annual temperature, tree cover, ruggedness and fox presence/absence. For islands smaller than Tasmania, island area was also included as a predictor of density (small islands have higher cat densities). The dashed lines indicate the Tropic of Capricorn.

Feral cat diet in Australia

Doherty, T.S., R. A. Davis, E. J. B. van Etten, D. Algar, N. Collier, C.R. Dickman, G. Edwards, P. Masters, Russell Palmer & S. Robinson. 2015. A continental-scale analysis of feral cat diet in Australia. Journal of Biogeography.

Aim
Reducing the impacts of feral cats (Felis catus) is a priority for conservation managers across the globe, and success in achieving this aim requires a detailed understanding of the species’ ecology across a broad spectrum of climatic and environmental conditions. We reviewed the diet of the feral cat across Australia and on Australian territorial islands, seeking to identify biogeographical patterns in dietary composition and diversity, and use the results to consider how feral cats may best be managed.

Location
Australia and its territorial islands.

Methods
Using 49 published and unpublished data sets, we modelled trophic diversity and the consumption of eight food groups against latitude, longitude, mean temperature, precipitation, environmental productivity and climate-habitat regions.

Results
We recorded 400 vertebrate species that feral cats feed on or kill in Australia, including 28 IUCN Red List species. We found evidence of continental-scale prey-switching from rabbits to small mammals, previously recorded only at the local scale. The consumption of arthropods, reptiles, rabbits, rodents and medium-sized native mammals varied with different combinations of latitude, longitude, mean annual precipitation, temperature and environmental productivity. The frequency of rodents and dasyurids in cats’ diets increased as rabbit consumption decreased.

Main conclusions
The feral cat is an opportunistic, generalist carnivore that consumes a diverse suite of vertebrate prey across Australia. It uses a facultative feeding strategy, feeding mainly on rabbits when they are available, but switching to other food groups when they are not. Control programmes aimed at culling rabbits could potentially decrease the availability of a preferred food source for cats and then lead to greater predation pressure on native mammals. The interplay between cat diet and prey species diversity at a continental scale is complex, and thus cat management is likely to be necessary and most effective at the local landscape level.

To eradicate feral cats, we need to know how many are out there

From https://theconversation.com/

During a speech in Parliament on October 17 1996 — 18 years ago today — then Liberal MP Richard Evans called for the “total eradication of domestic and feral cats from the Australian mainland and offshore islands by the year 2020”.

Similarly, Federal Environment Minister Greg Hunt last week announced a 10-year plan to eradicate “all of the significant populations of feral cats around Australia”.

A feral cat in the bush. Tim Doherty,

There has also been a lot of media recently about feral cats in Australia, including: Radio National’s Background Briefing, ABC Online, the Sydney Morning Herald, Radio National’s Bush Telegraph and The Australian

It’s great that the national conversation is gaining momentum on this issue. Australia has lost 30 mammal species to extinction in just over 200 years, which is the worst mammal extinction record anywhere in the world. According to Professor John Woinarski at Charles Darwin University, at least 20 of these can be attributed to cats.

A recent wave of mammal declines in parts of northern Australia, such as Kakadu National Park, has sparked a renewed call for action on feral cats.

But how many cats are out there? If we look at the evidence, we really don’t know.

Cats among the main causes of bird mortality

Erickson, W. P., Johnson, G. D., & Young Jr, D. P. (2005). A summary and comparison of bird mortality from anthropogenic causes with an emphasis on collisions. USDA Forest Service General Technical Report PSWGTR-191, 1029-1042.

We estimate that from 500 million to possibly over one billion birds are killed annually in the United States due to anthropogenic sources including collisions with human-made structures such as vehicles, buildings and windows, power lines, communication towers and wind turbines; electrocutions; oil spills and other contaminants; pesticides; cat predation; and commercial fishing by-catch. Many of the deaths from these sour- ces would be considered unlawful take under federal laws such as the Endangered Species Act, Migratory Bird Treaty Act, and the Bald and Golden Eagle Pro- tection Act. In this paper, we summarize this literature and provide the basis for the mortality projections for many of the apparent significant sources. Most of the mortality projections are based on small sample sizes, and on studies typically lacking adjustments for scav- enging and searcher efficiency biases. Although the estimates for each source often range by an order of magnitude, the cumulative mortality from all these sources continues to be a concern.

(There are more recent estimations in which cat's predation is 10 times more)

New evaluation of cat's kill in US: probably tens of billions kills per year

Loss, S.R., T. Will & P.P. Marra. 2013. The impact of free-ranging domestic cats on wildlife of the United States. Nature Communications 4, 1396 doi:10.1038/ncomms2380

Anthropogenic threats, such as collisions with man-made structures, vehicles, poisoning and predation by domestic pets, combine to kill billions of wildlife annually. Free-ranging domestic cats have been introduced globally and have contributed to multiple wildlife extinctions on islands. The magnitude of mortality they cause in mainland areas remains speculative, with large-scale estimates based on non-systematic analyses and little consideration of scientific data. Here we conduct a systematic review and quantitatively estimate mortality caused by cats in the United States. We estimate that free-ranging domestic cats kill 1.4–3.7 billion birds and 6.9–20.7 billion mammals annually. Un-owned cats, as opposed to owned pets, cause the majority of this mortality. Our findings suggest that free-ranging cats cause substantially greater wildlife mortality than previously thought and are likely the single greatest source of anthropogenic mortality for US birds and mammals. Scientifically sound conservation and policy intervention is needed to reduce this impact.

See also this entry.


Read more national surveys results on cat predation

100 millions prey in five months in UK!!

Woods, M., R.A. McDonald & S. Harris. 2003. Predation of wildlife by domestic cats Felis catus in Great Britain. Mammal Review 33 (2), 174-188.

1. A questionnaire survey of the numbers of animals brought home by domestic cats Felis catus was conducted between 1 April and 31 August 1997. A total of 14 370 prey items were brought home by 986 cats living in 618 households. Mammals made up 69% of the items, birds 24%, amphibians 4%, reptiles 1%, fish <1%, invertebrates 1% and unidentified items 1%. A minimum of 44 species of wild bird, 20 species of wild mammal, four species of reptile and three species of amphibian were recorded.

2. Of a sample of 696 individual cats, 634 (91%) brought home at least one item and the back-transformed mean number of items brought home was 11.3 (95% CI 10.4–12.2). The back-transformed means and number of cats retrieving at least one item from each prey group were: 8.1 (7.4–8.9) mammals for 547 (79%) cats, 4.1 (3.8–4.5) birds for 506 (73%) cats, 2.6 (2.2–3.0) herpetofauna for 145 (21%) cats and 2.2 (1.8–2.7) other items for 98 (14%) cats. 

3. The number of birds and herpetofauna brought home per cat was significantly lower in households that provided food for birds. The number of bird species brought home was greater in households providing bird food. The number of birds and herpetofauna brought home per cat was negatively related to the age and condition of the cat. The number of mammals brought home per cat was significantly lower when cats were equipped with bells and when they were kept indoors at night. The number of herpetofauna brought home was significantly greater when cats were kept in at night.

4. Based on the proportion of cats bringing home at least one prey item and the backtransformed means, a British population of approximately 9 million cats was estimated to have brought home in the order of 92 (85–100) million prey items in the period of this survey, including 57 (52–63) million mammals, 27 (25–29) million birds and 5 (4–6) million reptiles and amphibians.

5. An experimental approach should be taken to investigate the factors found by this descriptive survey to influence the numbers of prey brought home by cats. In particular, investigation of potential management practices that could reduce the numbers of wild animals killed and brought home by cats will be useful for wildlife conservation, particularly in suburban areas.


Read more national surveys results on cat predation

Read a short review about belling effectiveness

1.000.000.000 birds per year in USA!!

Dauphine, N. & R.J. Cooper. 2009. Impacts of free-ranging domestic cats (Felis catus) on birds in the United States: a review of recent research with conservation and management recommendations. Proceedings of the Fourth International Partners in Flight Conference: Tundra to Tropics: 205–219

Las aves americanas se enfrentan a un estimado de 117 a 157 millones de depredadores exóticos en la forma de gatos domésticos (Felis catus) en condición de libertad, los cuales probablemente matan anualmente al menos, mil millones de aves cada año en Estados Unidos. Los gatos han contribuido a la declinación y extinción de las aves a nivel mundial, y pueden ser la mayor causa de la extinción global de las aves luego de la destrucción de hábitat.  En este articulo, yo reviso la reciente investigación científica sobre el impacto que los gatos en condición de libertad causan a las poblaciones de aves en los Estados Unidos, con énfasis en su amenaza a las aves migratorias. Estudios han demostrado que los gatos constituyen una  amenaza importante para muchas poblaciones de aves, incluyendo aquellas especies cuya conservación es prioritaria, a través de la depredación de adultos, las nidadas y los juveniles, compitiendo también con depredadores nativos, tales como las aves de presa. En adicción a la mortalidad directa causada, los gatos causan reducciones en la fecundidad y supervivencia en las aves expuestas al riesgo de depredación,  las mismas que potencialmente y substancialmente dañan y reducen las poblaciones.  Acciónas efectivas para la conservación de las aves requerirá del fortalecimiento y aplicación de leyes que prohíben los gatos en condición de libertad, muchas de las cuales ya han sido promulgadas, así como también una mejora sustancial en la educación y que este esfuerzo por enfrentar los problemas que son causados por los gatos llegue al público en general, y producir métodos para controlar las poblaciones y movimientos de los gatos en condición de libertad.

Feral cat at an illegal cat colony in McAllen, TX, February 2008

 American birds face an estimated 117 to 157 million exotic predators in the form of free-ranging domestic cats (Felis catus), which are estimated to kill at least one billion birds every year in the United States. Cats have contributed to declines and extinctions of birds worldwide and are one of the most important drivers of global bird extinctions. In this paper, we review recent scientifi c research on the impacts of free-ranging cats on birds, with an emphasis on threats to migratory landbirds in the United States. Studies have shown that cats pose threats to many bird populations, including priority species for conservation, through their predation of adult, nestling, and juvenile birds. Cats also have impacts on birds through competition with native predators such as raptors, and through the harboring and transmission of zoonotic and other diseases to birds and other wildlife. In addition to direct mortality, cats may also cause stress responses in birds due to predation risk that may result in bird population declines. A substantial increase in public outreach is urgently needed to educate citizens about the conservation and welfare problems caused and faced by outdoor cats. Effective cat and wildlife management in this context will also require strengthening and enforcing policies and laws that control outdoor cats, many of which are already in place.

Cat-killed Eastern Towhee (Pipilo erythrophthalmus), a PIF-designated species of regional conservation concern, Athens, GA, January 2008

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Rural free-ranging domestic cats: a survey

Coleman, J. S., & Temple, S. A. (1993). Rural residents' free-ranging domestic cats: a survey. Wildlife Society Bulletin, 21(4), 381-390.

Nationwide, approximately 30% of households have cats. In rural areas where free-ranging cats are usually not regarded as pets, approximately 60% of households have cats. In the state of Wisconsin alone, with approximately 550,000 rural households, the number of rural free-ranging cats (not house pets) may be as high as 2 million. In some parts of rural Wisconsin, densities of free-ranging cats reach 114 cats per square mile. In these areas, cats are several times more abundant than all mid-sized native predators (such as foxes, raccoons, skunks) combined.

Read more national surveys results on cat predation