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 1.3–4.0 billion birds and 6.3–22.3 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.
Similar content being viewed by others
Christopher A. Lepczyk, Jean E. Fantle-Lepczyk, … John C. Z. Woinarski.
Jennifer L. McDonald & Elizabeth Skillings
Justin P. Suraci, Justine A. Smith, … Christopher C. Wilmers
Domestic cats, or Felis catus, are predators that have been brought to the world by humans1,2, and they are among the top 100 invasive non-native species worldwide3. Cats that roam freely on islands have resulted in or helped cause 14% of the contemporary bird, mammal, and reptile extinctions documented by the International Union for Conservation of Nature (IUCN) Red List. Growing data across three continents suggests that cats can also locally lower mainland populations of birds and mammals5,6,7 and contribute significantly to overall wildlife mortality8,9, 10. Despite these negative effects, animal welfare concerns—rather than ecological considerations—determine policies for the management of free-ranging cat populations and the control of pet ownership behaviors11. Trap-Neuter-Return (TNR) colonies and other projects aimed at managing free-ranging cats have the potential to negatively impact wildlife populations. However, these initiatives are being carried out across the United States without adequate public awareness, scientific evidence, or the environmental review procedures that are usually necessary for actions that have an adverse effect on the environment11,12.
The argument that the overall mortality from cat predation is insignificant when compared to other anthropogenic threats, such as collisions with man-made structures and habitat destruction, is a primary cause of the current non-scientific approach to managing free-ranging cats. However, in addition to estimating the overall number of fatalities, determining which species are being killed (e.g., native versus non-native invasive species and rare versus common species) is necessary to evaluate the conservation importance of a mortality source. The estimated annual bird mortality in the United States due to predation by all cats, owned and unowned, is in the hundreds of millions13,14. When we talk about unowned cats, we mean farm/barn cats, strays who are fed by people but are not allowed to live in homes, cats in subsidized colonies, and feral cats. With this magnitude, cats would rank among the leading causes of anthropogenic bird mortality; however, collisions with windows and buildings may be even more deadly15,16,17 Current estimates of cat predation mortality are speculative and not grounded in empirical research13,14,15,16, or, at most, derived from extrapolating findings from a single study18. Furthermore, there are no comprehensive mortality data for mammals, despite the fact that they make up a sizable portion of cat diets.
Data-driven systematic reviews of studies estimating owned and unowned cat predation rates were carried out, and the amount of bird and mammal mortality caused by all cats in the contiguous United States (all states except Alaska and Hawaii) was estimated. We estimate that free-ranging domestic cats kill 1. 3–4. 0 billion birds and 6. 3–22. 3 billion mammals each year, with the majority of this mortality coming from unowned cats. This level of mortality is potentially higher than all other sources of anthropogenic mortality of US birds and mammals, and it is far higher than previous estimates of cat predation on wildlife.
A team of researchers recently added up all the species on these invaders’ menu. In a paper published on Tuesday in Nature Communications, the team compiled a database of more than 2,000 species that have fallen victim to free-ranging domestic cats. Nearly 350 of these species are of conservation concern, and several are already extinct. “We don’t really know of any other mammal that eats this many different species,” says the study’s lead author Christopher Lepczyk, an ecologist at Auburn University. “It’s almost like an indiscriminate eater; they’re eating whatever’s available.”
To ascertain each species’ conservation status, the researchers cross-checked their newly created database with the Red List of Threatened Species maintained by the International Union for Conservation of Nature. They discovered that 347 species known to have been eaten by cats are classified as extinct, near threatened, threatened, or endangered (some of which are critically endangered or endangered). Many of these are endemic to islands without natural predators resembling cats, leaving prey gullible and comparatively helpless. These animals include small birds, mammals, and reptiles. Eleven species that were found to consume cats during the study, such as the white-footed rabbit rat (Conilurus albipes), New Zealand quail (Coturnix novaezelandiae), and Hawaiian crow (Corvus hawaiiensis), are currently considered extinct in the wild.
With their retractable claws, sharp fangs, and night vision, domestic cats (Felis catus), despite their diminutive size and memeable mugs, are perfectly suited killing machines. And these potent predators are anything but picky. Over the course of the last 9,000 years, as humans have spread cats throughout the world, these vicious cats—likely domesticated thousands of years ago in the Near East—have terrorized native species on every continent save Antarctica.
Lepczyk hopes that by offering a thorough analysis of the food that free-ranging cats consume, policy makers and conservationists will be better able to combat the feline invasion, even though the new list may not be complete yet. Lepczyk asserts, “We can solve the problem of cats,” particularly if the animals are kept from roaming freely through their natural habitats. Ultimately, individuals must be responsible pet owners. ”.
“The research confirms that cats are the most adaptable and all-around predator,” says Sarah Legge, an Australian wildlife ecologist who was not involved in the recent publication. According to Legge, who studies how cats affect Australian wildlife, one of the biggest dangers to the biodiversity of the continent is cats. “If we don’t manage cats, there will inevitably be more extinctions as cats continue to cause population declines,” she continues. “Predation by a versatile predator with a relatively fast reproductive rate is beyond the capabilities of Australia’s native fauna.” ”.
Data extraction and standardization of predation rates
The majority of studies provide data that allowed us to calculate the cat predation rate or provide an estimate of the rate (i.e., the amount of prey killed per cat on a daily, monthly, or annual basis). We computed separate predation rates by extracting taxa-specific prey counts from tables or figures and multiplying the total predation rate by the percentage of prey items in each taxon when studies only provided estimates of the predation rates for all wildlife combined. If taxa-specific counts were missing, we got in touch with the authors directly to find out. We used the average and medium values, respectively, for studies that presented low, medium, and high estimates, or low and high estimates. We determined the average predation rate for studies that provided multiple estimates of predation for cats with comparable ranging behaviors (e.g., owned cats in rural and urban areas).
The majority of research on feral cats reports the quantity or frequency of various taxa found in the stomachs and/or scats. When estimating annual predation rates for studies that reported the number of prey items, we made the assumption that one stomach or scat sample represented the average daily prey intake of a cat (e.g., an average of one prey item per stomach or scat=365 prey per cat per year). Since cats typically digest prey within 12 hours, this assumption probably led to conservative estimates (ref). 2828) and can produce two or more scats each day29. In research papers disclosing the occurrence frequencies of prey items, we assumed that this percentage represented a cat%E2%80%99s%20average%20daily%20prey%20intake%20(for instance, a%2010%%20bird%20occurrence%20rate=0). 1 bird per stomach or scat=36. 5 birds per cat per year). Although estimates from this approach are even more conservative than those from the first assumption, this assumption produces coarse estimates of the predation rate because many stomachs and scats most likely contained multiple birds or mammals.
Numerous studies’ estimates of the predation rate were based on repeated sampling occasions throughout the year or on continuous year-round sampling. However, seasonal coverage of some studies was incomplete. In these cases, we adjusted partial-year predation estimates based on the average monthly prey proportion taken from year-round studies that reported monthly data (birds and mammals8,33, birds only7,40) to generate full-year predation rate estimates. We deducted six months from monthly estimates from studies conducted in the southern hemisphere for partial-year estimates derived from the northern hemisphere. Supplementary Table S1 presents the final estimates of the annual predation rates for every study. The year-round studies we used are representative of various geographical regions with slightly different seasonal patterns of predation and varying climates (England and Australia for mammals, and Kansas (US), Australia, and New Zealand for birds). The average of full-year studies for both birds and mammals showed that the proportions of predation in the spring and summer were higher than in the fall and winter, which is a pattern that is expected for most of the United States. Therefore, the reference studies we consulted offer a fair starting point for adjusting to full-year mortality estimates. This method significantly enhances the presumption that mortality is minimal throughout the year that is not sampled.
FAQ
What birds have cats made extinct?
How many species have cats caused extinction?
How many birds are endangered because of cats?
How many birds are killed by house cats?