Cat predation on wildlife is the result of the natural instincts and behavior of both feral and owned house 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; 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. As an invasive species[1] and predator,[2] they do considerable ecological damage.[2] Cats kill billions of wild birds each year. This feral cat near
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.[3]
In Australia, hunting by feral cats helped to drive at least 20 native mammals to extinction,[4] and continues to threaten at least 124 more.[4] Their introduction has caused the extinction of at least 33 endemic species on islands throughout the world.[2] A 2013 systematic review in Nature Communications of data from 17 studies found that feral and domestic cats kill billions of birds in the United States every year.[5]
In a global 2023 assessment, cats were found to prey on 2,084 different species, of which 347 (or 16.5%) 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.[6]
Impact on island ecosystems edit
Many islands host ecologically naive animal species. That is, creatures like cats that lack predatory responses to deal with predators [13] The biodiversity of these islands has been severely impacted by the introduction of pet cats. [14].
A number of species and local extinctions have been linked to them, including the Guadalupe storm petrel from the Pacific coast of Mexico, the hutias from the Caribbean, and the Lyalls wren from New Zealand. They were found to be a significant cause of the extinction of 2040% of the studied species in a statistical study. The statement “no other alien predator has had such a universally damaging effect” was written by Moors and Atkinson in 1984. [13].
The sole large animal population of the isolated Kerguelen Islands in the southern Indian Ocean consists of cats, rabbits, and a few seabirds. Though their primary source of food is exotic mammals, cats have a significant impact on seabirds. [15].
Many conservationists engaged in the field of island restoration have attempted to eradicate feral cats due to the harm that these animals can cause to islands and certain ecosystems. (Removing introduced species and reintroducing native species is the process of island restoration.) 48 islands, including Australia’s Macquarie Island and New Zealand’s network of offshore island bird reserves, had completely eradicated their feral cat populations as of 2004.
Larger initiatives have also been carried out, such as their total evacuation from Ascension Island. The 19th-century introduction of cats led to a decline in seabird nesting populations. The initiative to eradicate them from the island started in 2002, and by 2004 there were no cats left on it. Seven seabird species that had been absent from the island for a century have since made a comeback. [17][unreliable source?].
In some cases, the removal of cats had unintended consequences. As an illustration, consider Macquarie Island, where the eradication of cats led to an enormous increase in rabbit populations that began consuming the island’s vegetation and protecting the birds from other predators like rats and other birds. even when the eradication was done inside the context of an integrated pest management framework [18][19][20]. [21][unreliable source?] The rats and rabbits were supposed to be removed in 2007, but it might take up to seven years and $24 million. [22].
Factors explaining estimate uncertainty
Sensitivity analyses showed that unowned cat parameters explained the largest variation in total mortality estimates for both mammals and birds (Fig. 2). The population size of unowned cats explained the largest variation in mortality estimates (42% for birds and 2051% for mammals), while the rate of unowned cat predation explained the second-greatest variation (24% for birds and 2040% for mammals). The sole additional factors that clarified
The percentages represent adjusted R2 values from multiple regression models. This table shows the amount of variation in estimates of wildlife mortality in the contiguous United States that is contributed by each parameter in the cat predation model.
Our estimate of bird mortality is significantly higher than any previous US estimates for cats13,14,16, as well as estimates for any other direct cause of human death, such as pesticide poisoning13,15,16,17,18,19,20, and 21 and collisions with windows, buildings, communication towers, and cars. For other sources of anthropogenic mortality, systematic reviews similar to ours—which comprise protocol formulation, a data search strategy, data inclusion criteria, data extraction, and formal quantitative analyses22—are hard to come by. 21 Raising the accuracy of mortality estimates ought to be a top priority since it will make mortality sources more comparable.23 However, our estimate for cat predation is the first to be based on rigorous data-driven methods, and no estimate of any other source of anthropogenic mortality approaches the value we determined for it. The actual number of birds killed may exceed our estimates because, among other things, we excluded high local predation rates and made assumptions that resulted in minimum predation rate estimates for cats that are not owned.
Amphibians and reptiles in the United States may be significantly impacted by free-roaming cats. There are, however, few US studies on cat predation on these taxa. We used the same cat predation model and estimates of cat predation rates on these taxa from studies conducted in Europe, Australia, and New Zealand to produce a first approximation of US predation rates on reptiles and amphibians. In the contiguous United States, we calculate that cats may kill between 228 and 871 million reptiles (median=478 million) and between 86 and 320 million amphibians (median=173 million) annually. The regions where we collected predation data for these taxa and the United States may have different populations of reptiles and amphibians, and consequently, different cat predation rates. Furthermore, throughout most of the United States during the winter, reptiles and amphibians are not available as prey. More investigation is required to fully understand the effects of cats on the herpetofauna in the United States, particularly in light of the various human-caused stressors that pose a threat to their populations (such as habitat loss, infectious diseases, and climate change) and the documented extinctions of amphibians and reptiles in other areas as a result of cat predation4,24.
Individual US studies that show high annual predation rates by individual unowned cats exceeding 200 mammals per year6,25,26,27,28 and the consistent finding that cats preferentially depredate mammals over other taxa (Supplementary Table S1) support the exceptionally high estimate of mammal mortality from cat predation. Based on an estimated population of between 30 and 80 million unowned cats, annual mortality for unowned cats alone would range from 3 to 8 billion mammals, even with a lower yearly predation rate of 100 mammals per cat. We are not aware of any studies that have methodically measured direct anthropogenic mortality of small terrestrial mammals over broad scales, but this estimated level of mortality may surpass any other direct source of anthropogenic mortality for small mammals.
Most bird species that cats prey on are native species. In studies conducted in 2010 using specimens from 2058 different species, on average, only 2033% of the bird prey items identified to species were non-native species (Supplementary Table S3). Mammal predation patterns on native and non-native species are less evident and seem to differ depending on the type of landscape. Native small mammals are less common in densely populated urban areas, so non-native species of rats and mice can comprise a significant portion of mammalian prey29. However, research on animals in suburban and rural areas discovered that native mice, shrews, voles, squirrels, and rabbits accounted for 2075–80% of the total number of mammalian prey.26,30,31 To understand the patterns of predation by owned and unowned cats on native and non-native mammals, as well as across various landscape types, more research on mammals is required.
Sensitivity analyses show that more study on cats that are not owned will continue to increase the accuracy of death estimates. Our conclusion that the size of the unowned cat population and the rate of predation accounted for the most variation in mortality estimates highlights the current state of ignorance regarding unowned cats. Due to the high expense of obtaining a precise estimate of the unowned cat population in the United States and the fact that feral cats are usually solitary and fearful of humans, no precise estimate of the unowned cat population exists for the country. Furthermore, unowned cats are kept in human-subsidized colonies without the general public being aware of it. For instance, just in Washington, DC, there are A wildlife mortality reporting database can benefit from the inclusion of observations of cats living in the wild to enhance population size estimates23.
Comparing mortality estimates to estimates of individual species’ population abundance provides context for the population impact of a mortality source. However, due to spatiotemporal variation in numbers, estimates of wildlife population abundance at the continental scale are uncertain. The lack of national population estimates for mammals makes it more difficult to understand how cat predation affects populations. The estimates for all land birds in North America that are most vulnerable to mainland cat predation (Supplementary Table S3) vary from 10 to 20 billion individuals32. It is challenging to determine which species and populations are most vulnerable due to a lack of information regarding the relative proportions of various bird species killed by cats and the spatiotemporal variation of these proportions. Our mortality estimates’ magnitude indicates that cats are probably contributing to some species’ and some regions’ population declines. The effects of cat predation are most likely to affect threatened and endangered wildlife species on islands, and this may also be true for vulnerable species in specific mainland areas5, as even a small number of deaths could result in large population declines. Cat colonies are a wildlife management priority because they provide an exceptionally high level of risk to threatened species nearby, including managed TNR colonies11,12. Peer-reviewed scientific studies11 do not support claims that TNR colonies are effective in reducing cat populations and, consequently, wildlife mortality.
Our estimates should serve as a warning to the public and policy makers about the significant amount of wildlife mortality brought on by free-ranging cats. A quantitative evidence base is necessary for well-informed decisions regarding actions to minimize wildlife mortality. We present evidence of widespread impacts of cat predation derived from a methodical examination of numerous data sources. Future specific management decisions pertaining to cats, both domestically and internationally, need to be further informed by fine-scale research that enables the evaluation of the efficacy of different management strategies and the analysis of population responses to cats. We do not imply that other man-made hazards that result in fewer deaths are inconsequential to biology. Regarding the cumulative effects of multiple mortality sources on the population, almost nothing is known. Furthermore, the development of conservation objectives and risk prioritization are limited by the comparison of total mortality numbers. The most information regarding the likelihood of population-level effects of cat predation can be obtained by combining estimates of mortality per species with estimates of population size. Even though our findings indicate that owned cats have a smaller overall impact than unowned cats, owned cats nevertheless significantly increase wildlife mortality (Table 2); therefore, it is important to look into easy ways to lower pet-related mortality, like restricting or banning outdoor access. To improve the sustainability of wildlife populations, efforts must be made to more accurately measure and reduce mortality from all anthropogenic threats.
The extent of feline-related wildlife mortality that we present here far outweighs all previous estimates. The evidence that is currently available indicates that cat predation mortality is probably significant in every region of the world where cats live in freedom. This mortality is especially concerning in light of the steadily rising numbers of owned cats, the possibility of rising numbers of unowned cats, and the growing number of direct and indirect mortality sources endangering wildlife in the US and around the world.
To find studies that show cat predation on birds and mammals, we searched JSTOR, Google Scholar, and the Web of Science database (formerly ISI Web of Science) within the Thomson Reuters Web of Knowledge search engine. Because there was a small sample size of US studies, we decided to broaden our search to include predation research from other temperate regions. Additionally, we looked for US studies that estimated the percentage of owned cats that have access to the outdoors and the percentage of cats that hunt wildlife, as well as studies that provided estimates of cat population sizes at the scale of the contiguous United States. We searched for the following terms: “domestic cat” plus “predation,” “prey,” “diet,” “food item,” and “mortality”; all previous terms with “domestic cat” substituted for “Felis catus,” “feral,” “stray,” “farm,” “free-ranging,” and “pet”; “trap-neuter-return colony”; “TNR colony”; and “cat predation” plus “wildlife,” “bird,” “mammal,” and “rodent.” We looked through article references to find more pertinent research. We also got in touch with the lead authors of three studies to ask if they were aware of any completed or ongoing unpublished studies on cat predation in the US.
United Kingdom edit
It is customary in the UK to permit indoor access for feline companions. [39] SongBird Survival believes that “the prevailing line that there is no scientific evidence that predation by cats is having any impact on bird populations in the UK is simply no longer tenable”[40] 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 three times as many songbirds as sparrowhawks; the mere presence of cats near bird nests was found to decrease provision of food by a third while the subsequent 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 [40].
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