Cat predation on wildlife
Cat predation on wildlife is the result of the natural instincts and behavior of feral and owned house cats to hunt small prey, including wildlife. Some people view this as a desirable trait, such as in the case of barn cats and other cats kept for the intended purpose of pest control in rural settings; but scientific evidence does not support the popular use of cats to control urban rat populations, and ecologists oppose their use for this purpose because of the disproportionate harm they do to native wildlife. Recognized as both invasive species and predators, cats have been shown to cause significant ecological harm across various ecosystems.
Due to cats' natural hunting instinct, their ability to adapt to different environments, and the wide range of small animals they prey upon, both feral and free-ranging pet cats are responsible for predation on wildlife, and in some environments, considerable ecological harm. Cats are disease carriers and can spread diseases to animals in their community and marine life. There are methods to help mitigate the environmental impact imposed by feral cats through different forms of population management. Reducing cats' impact on the environment is limited by perceptions society has towards cats because humans have a relationship with cats as pets.
In Australia, hunting by feral cats helped to drive at least 20 native mammals to extinction, and continues to threaten at least 124 more. Their introduction into island ecosystems has caused the extinction of at least 33 endemic species on islands throughout the world. A 2013 systematic review in Nature Communications of data from 17 studies found that feral and domestic cats are estimated to kill billions of birds in the United States every year.
In a global 2023 assessment, cats were found to prey on 2,084 different species, of which 347 were of conservation concern. Birds, reptiles, and small mammals accounted for 90% of killed species. Island animals of conservation concern had three times more species predated upon than continental species.
Consequences of introduction
Many islands host ecologically naive animal species. That is, animals that do not have predator responses for dealing with predators such as cats. Pet cats introduced to such islands have had a devastating impact on these islands' biodiversity.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 the Lyall's wren from New Zealand. In a statistical study, they were a significant cause for the extinction of 40% of the species studied. Moors and Atkinson wrote, in 1984, "no other alien predator has had such a universally damaging effect".
The large animal population of the remote Kerguelen Islands in the Southern Indian Ocean comprises introduced species, including cats, rabbits, some seabirds, and sheep. Although exotic mammals form the bulk of their diet, cats' impact on seabirds is very important.
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. , 48 islands have had their feral cat populations eradicated, including New Zealand's network of offshore island bird reserves 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. As of 2007, five species of seabirds had re-established colonies on the main island.
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 off the island's vegetation, thus leaving the birds without protection from other predators, like rats and other birds. even if the eradication was positioned within an integrated pest management framework. The removal of the rats and rabbits was scheduled for 2007 and it could take up to seven years and cost $24 million.
Prey
Cats are generalist predators that hunt a broad range of prey including mammals, birds, fish, reptiles, amphibians, and invertebrates. One study in Italy found that cats there returned 207 different species of prey, while another on Great Britain found cats were hunting 20 different species of mammal, 44 species of bird, four reptile species and three species of amphibian.Mammals
Small mammals, particularly rodents, are the main prey of the african wild cat, the primary ancestors of the domestic cat. For cats, similarly, small mammals usually make up the majority of captured prey, but this varies with whatever types of prey are locally available. In this context, cats are also frequently used as a form of pest control.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.
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. Studies have found that house mouse and rat infestations are more common in locations near where outdoor cats are being fed, despite occasional predation by the cats.
Birds
A 2013 study by Scott R. Loss and colleagues from the Smithsonian Conservation Biology Institute and the U.S. Fish and Wildlife Service identified free-ranging domestic cats as the leading human-caused threat to birds and small mammals in the United States. The study estimated that cats kill between 1.3 and 3.7 billion birds and between 6.3 and 22.3 billion mammals each year, with unowned cats being responsible for the majority of these deaths. These figures were much higher than previous estimates for the U.S. 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.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. In Western Europe, cats are responsible for between 12.8% and 26.3% of all bird deaths, and between 2000 and 2015, cat-related mortality in garden birds increased by at least 50%.
Wildlife on islands faces unique challenges. A 2001 study attributed the decline of several island bird species, such as the Townsend's shearwater, socorro dove, and the Marquesan ground dove to predation by domestic cats. The study concluded that habitat loss and degradation were the primary threats to endangered bird species, impacting at least 52% of them, while introduced species, including domestic cats, rats and mustelids, accounted for 6% of endangered birds. Other studies caution that removing domestic cats from islands can have unintended ecological consequences, including surges in rat populations, which may further endanger native bird and mammal species.
Impact on island ecosystems
Around half of the scientific literature on cat predation of wildlife is focused on oceanic islands. The emphasis is due in part to the unique vulnerability of island fauna, which makes declines and extinctions due to cats easier to document on islands than elsewhere. In many cases, it is easier to eradicate cats from islands than from mainland areas, which allows studies on the effects of the removal on native prey species.Island species are particularly vulnerable to predation by invasive cats due to their evolutionary isolation. Many of these species lack natural defenses against mammalian predators because they have evolved in environments free from threats. The introduction of cats has led to significant population declines among vertebrate species, especially in ecosystems where prey populations are small and isolated, making it difficult for them to recover from ongoing predation. Their predation on native species can reduce populations to critically low levels, resulting in cascading effects on other species that occupy similar ecological roles. In the pacific, cats have caused declines in seabird populations, including Hawaiian petrel and Townsend's shearwater, both of which play vital roles in nutrient cycling by transferring marine-derived nutrients to terrestrial habitats. In the Caribbean, cats have significantly impacted reptiles such as iguanas, destabilizing population dynamics and interrupting essential ecosystem functions like herbivory and seed dispersal.
Impact by location
Australia
Cats in Australia have been found to have European origins. 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.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. 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. Some inhabitants have begun eating cat meat to mitigate the harm that wild cats do to the local wildlife.
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.
Feral and pet cats in Australia are estimated to kill around 650 million lizards and snakes per year, or about 225 reptiles per cat on average. Cats were found to be actively hunting and killing over 250 different species of reptiles in Australia, with 11 of which being considered endangered species. Cats consume so many lizards in Australia that there was a single cat found with the parts of 40 individual lizards inside of its stomach, the highest amount recorded thus far.