Cat predation on wildlife

Cats kill billions of wild birds each year. This feral cat near Brisbane has caught a Pale-headed rosella.

Cat predation on wildlife is the result of the natural instincts and behavior of both feral and domesticated cats to hunt small prey, including wildlife. Some people view this as a desirable phenomenon, such as in the case of barn cats and other cats kept for the intended purpose of pest control; however, contrary to popular belief, there is no scientific evidence that cats are an effective means of rodent control, and ecologists oppose their use for this purpose because of the disproportionate harm they do to beneficial native wildlife. As an invasive species^[1] and superpredator,^[2] they do considerable ecological damage.^[2] In Australia, hunting by cats helped to drive at least 20 native mammals to extinction,^[3] and continues to threaten at least 124 more.^[3] Their introduction has caused the extinction of at least 33 endemic species on islands throughout the world.^[2] Feral and domestic cats kill billions of birds in the United States every year, where songbird populations continue to decline.^[4]

Birds[]

A feral cat with an American Robin. Plate from Forbush (1916).

A 2013 study by Scott R. Loss and others of the Smithsonian Conservation Biology Institute and the U.S. Fish and Wildlife Service found that free-ranging domestic cats (mostly unowned) are the top human-caused threat to wildlife in the United States, killing an estimated 1.3 to 3.7 billion birds and 6.3 to 22.3 billion mammals annually.^[4][5] These figures were much higher than previous estimates for the U.S.^[4]:2 Unspecified species of birds native to the U.S. and mammals including mice, shrews, voles, squirrels and rabbits were considered most likely to be preyed upon by cats.^[4]:4

Perhaps the first U.S. study that pointed to predation by cats on wildlife as a concern was ornithologist Edward Howe Forbush's 1916 report for the Massachusetts State Board of Agriculture, The Domestic Cat: Bird Killer, Mouser and Destroyer of Wildlife: Means of Utilizing and Controlling It.^[6]

Island settings pose particular challenges for wildlife. A 2001 study identified cats alone as responsible for the plight of some island bird species, such as the Townsend's shearwater, socorro dove, and the Marquesan ground dove.^[7]:400 The same study identified the greatest cause of endangerment of birds as habitat loss and degradation, with at least 52% of endangered birds affected,^[7]:399 while introduced species on islands, such as domestic cats, rats and mustelids,^[7]:403 affected only 6% of endangered birds.^[7]:399 Other studies caution that removing domestic cats from islands can have unintended consequences, as increasing rat populations can put native bird^[8] and mammal species^[9][10] at risk.

Impact by location[]

Australia[]

Cats in Australia have been found to have European origins.^[11] This is important to note because of their effect on native species. Feral cats in Australia have been linked to the decline and extinction of various native animals. They have been shown to cause a significant impact on ground nesting birds and small native mammals.^[12]

Feral cats have also hampered any attempts to re-introduce threatened species back into areas where they have become extinct as the cats have hunted and killed the newly released animals.^[13] Numerous Australian environmentalists claim the feral cat has been an ecological disaster in Australia, inhabiting most ecosystems except dense rainforest, and being implicated in the extinction of several marsupial and placental mammal species.^[14] Some inhabitants have begun eating cat meat to mitigate the harm that wild cats do to the local wildlife.^[15]

In 2020, it was reported that a culling of feral cats that had recently begun in Dryandra Woodland, in Western Australia, had caused the population of numbats to triple in number, the largest number of the endangered marsupial to have been recorded there since the 1990s.^[16]

China[]

Domestic cats are common throughout China, and the number of pet cats in the country increased at a rate of 8.6% from 2018 to 2019. A 2021 estimate based on a public survey estimated that outdoor cats kill "1.61–4.95 billion invertebrates, 1.61–3.58 billion fishes, 1.13–3.82 billion amphibians, 1.48–4.31 billion reptiles, 2.69–5.52 billion birds, and 3.61–9.80 billion mammals" there each year.^[17] The authors recommended policies be implemented, such as a public education initiative to encourage people to keep their cats indoors, and building more animal shelters. They also recommended that TNR programs "should be limited until rigorous, peer-reviewed studies are able to show that such efforts consistently attain the sterilization rates needed to result in stabilization and permanent decline of unowned cat populations," as they said that most TNR programs fail to do this.^[17]

New Zealand[]

The fauna of New Zealand has evolved in isolation for millions of years without the presence of mammals (apart from a few bat species). Consequently, birds dominated the niches occupied by mammals and many became flightless. The introduction of mammals after settlement by Māori from about the 12th century had a huge effect on indigenous biodiversity. European explorers and settlers brought cats on their ships and the presence of feral cats was recorded from the latter decades of the 19th century.^[18] It is estimated that feral cats have been responsible for the extinction of six endemic bird species and over 70 localised subspecies as well as depleting bird and lizard species.^[19]

United Kingdom[]

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In the UK, the Royal Society for the Protection of Birds says there is no scientific evidence that predation by cats is having any effect on the population of birds UK-wide. They say that starvation and disease, and predation by other animals, are greater drivers of bird mortality, and that cats preferentially kill "weak or sickly" birds. They also say that the bird species that are showing the most serious population declines don't commonly encounter cats. They attribute the decline in bird populations to habitat loss.^[20]

Nick Forde, a trustee of the UK charity SongBird Survival, said the RSPB's claim of no evidence was disingenuous because adequate studies had not been done, in part due to the RSPB's position. Forde accused the RSPB of downplaying the effect of cat predation on birds in the UK to avoid offending "old ladies who might own cats", who he said are some of the RSPB's most generous benefactors. The RSPB's head of nature policy, Jeff Knott, denied that the agency was downplaying the effects of predation by cats. Knott said that cat predation was not a conservation issue, and that the RSPB was not afraid of potentially offending its members. He added that the Royal Society for the Protection of Birds had no plans to spend funds studying the effects of cat predation on birds.^[21]

In the UK, it is common to allow pet cats access to the outdoors.^[22] SongBird Survival considers that "the prevailing line that 'there is no scientific evidence that predation by cats is having any impact on bird populations in UK' is simply no longer tenable",^[23] and that "no study has ever examined the impact of cats on songbirds at the population level; evidence shows that the recovering sparrowhawk population in the 1970-80s resulted in the decline of some songbird populations; cats kill around 3 times as many songbirds as sparrowhawks; the mere presence of cats near birds' nests was found to decrease provision of food by a third while the resultant mobbing clamour from parent birds led in turn to increased nest predation by crows and magpies; [and that] it is therefore far more likely that cats have an even greater impact on songbird populations than sparrowhawks".^[23]

Sir David Attenborough in his Christmas Day, 2013, edition of BBC Radio 4 programme Tweet Of The Day said "cats kill an extraordinarily high number of birds in British gardens".^[24] Asked whether cat owners should buy bell collars for their pets at Christmas, he replied: "that would be good for the robins, yes".^[24]

Islands[]

Consequences of introduction[]

Lyall's wren became extinct within two years of the introduction of cats to Stephens Island.

Many islands host ecologically naive animal species. That is, animals that do not have predator responses for dealing with predators such as cats.^[25] Feral cats introduced to such islands have had a devastating impact on these islands' biodiversity.^[26]

They have been implicated in the extinction of several species and local extinctions, such as the hutias from the Caribbean, the Guadalupe storm petrel from the Pacific coast of Mexico, and Lyall's wren. In a statistical study, they were a significant cause for the extinction of 40% of the species studied.^[26] Moors and Atkinson wrote, in 1984, "no other alien predator has had such a universally damaging effect."^[25]

Feral cats, along with rabbits, some sea birds, and sheep, form the entire large animal population of the remote Kerguelen Islands in the southern Indian Ocean. Although exotic mammals form the bulk of their diet, cats' impact on seabirds is very important.^[27]

Restoration[]

Because of the damage cats cause in islands and some ecosystems, many conservationists working in the field of island restoration have worked to remove feral cats. (Island restoration involves the removal of introduced species and reintroducing native species.) As of 2004, 48 islands have had their feral cat populations eradicated, including New Zealand's network of offshore island bird reserves^[28] and Australia's Macquarie Island.

Larger projects have also been undertaken, including their complete removal from Ascension Island. The cats, introduced in the 19th century, caused a collapse in populations of nesting seabirds. The project to remove them from the island began in 2002, and the island was cleared of cats by 2004. Since then, seven species of seabird that had not nested on the island for 100 years have returned.^[29]

In some cases, the removal of cats had unintended consequences. An example is Macquarie Island, where the removal of cats caused an explosion in the number of rabbits, that started feeding of the island's vegetation, thus leaving the birds without protection to other predators, like rats and other birds^[30][31][32] even if the eradication was positioned within an integrated pest management framework.^[33] The removal of the rats and rabbits was scheduled for 2007 and it could take up to seven years and cost $24 million.^[34]

Mice and rats[]

Cats are sometimes intentionally released into urban environments on the popular assumption that they will control the rat population; but there is little scientific basis for this. The reality is that cats find rats to be large and formidable prey, and so they preferentially hunt defenseless wildlife such as lizards and songbirds instead. Scientists and conservationists oppose the use of cats as a form of rodent control because they are so inefficient at destroying pest species that the harm they do to native species in the process outweighs any benefit.^[35][36][37]

Despite this, cat rescue groups sometimes release unadoptable feral cats into rat-infested neighborhoods under the pretext of giving the cats "jobs" as rat control, as is being done in Chicago and Brooklyn; the cats will largely ignore the rats and instead will beg for food from people or eat garbage and whatever small wildlife they can catch. Jamie Childs, a public health researcher who has studied urban feral cats, told The Atlantic that he sees cats and rats peaceably eating from the same pile of garbage at the same time.^[38][39]

Cat attack outcomes[]

Wildlife that are attacked by cats fare poorly, even when provided with veterinary treatment by licensed wildlife rehabilitators (over 70% of mammals and over 80% of birds died in spite of treatment in one study).^{[40]:p. 171} Even those that had no visible injuries from the cat attack often died (55.8% of birds, 33.9% of mammals).^{[40]:p. 169} Typical wildlife injuries caused by cats include cuts, degloving (the stripping off of skin), and small puncture wounds caused by prey being gripped by the cat's teeth that are easily hidden by fur or feathers.^{[40]:p. 171} Systemic infection, usually caused by Pasteurella multocida, a highly pathogenic bacterial species that's found naturally in cat mouths, can kill small animals in as little as 15 hours.^{[40]:p. 171} Few other causes of injury that are commonly seen by wildlife care facilities lead to death as rapidly^{[40]:p. 171} or as frequently as interaction with a cat.^{[40]:p. 170}

Cat owner attitudes[]

Predation by pet cats is an environmental issue that cannot be resolved until cat owners accept that the problem exists and individually take responsibility for addressing it.^[41] Surveys of cat owners find they often view the depredation of wildlife as a normal thing that cats do, and rarely feel an individual obligation to prevent it.^[41] They may experience some level of cognitive dissonance toward the subject, because when surveyed they're more likely than the general public to believe that cat predation isn't harmful to wildlife, despite the likelihood they have witnessed acts of predation firsthand, and in many cases have been receiving "gifts" of animal carcasses from their cats.^[42] Those that express concern also often express a belief that, despite owning the animal, they have no control over what it does, or believe that they can't manage its behavior without compromising the cat's welfare in some way.^[41] A few cat owners even take pride in the animals their cats return home, believing it represents the cat's authenticity or skill.^[41]

See also[]

• Surplus killing, biology

References[]

Further reading[]

• Marra, Peter P.; Santella, Chris (2016). Cat Wars: The Devastating Consequences of a Cuddly Killer. Princeton University Press. ISBN 978-0691167411..