Domesticated house cats aren’t indigenous
Biology environment by

Domesticated house cats aren’t indigenous and have a significant impact on wildlife

The domestic cat, Felis silvestris catus, evolved from the African wild cat, Felis silvestris, between 3000 to 9000 years ago. There are small differences in appearance between wild and domestic cats, but genetically they are almost identical. In the last ice age (about 25.000 years ago), wild cats dispersed widely throughout Europe, Asia and Africa.

The domestic cat has been introduced in the wild by humans, deliberately and accidentally, into all continents except the mainland Antarctica. It has been listed among the 100 worst non-native invasive species in the world and is the most invasive predator introduced by man. Feral cats can have a severe influence on native animal populations, especially in seabirds on oceanic islands.

Roaming pet cats are a significant issue because they hunt, harass and compete with wildlife, they spread diseases to wildlife and people, compete with other predators, reduce the reproductive success of prey species by hunting, including small mammals, birds and insects and reduce the genetic integrity of wild felids by interbreeding.  

Regardless of how cats are kept (inside/outside house cats, free-ranging, feral or semi-feral), they have negative effects on native wildlife populations due to their predatory nature. Although most house cats are fed by their owners, this doesn’t stop their hunting behaviour. Feral and free-ranging cats can be present in high densities, which can potentially lead to devastating effects on native animals. Feral cat “colonies” form around a reliable food source, mostly provided (intentionally or unintentionally) by humans. Due to human assistance the population density of domestic cats is usually not limited by disease, food availability or lack of shelter, therefore their numbers are high, especially in urban areas and villages.

Scientific consensus supports that domestic cats are an invasive species; they have caused several extinctions, at least 63 vertebrate extinctions, impact native wildlife populations and transmit multiple zoonotic diseases. Despite these harmful effects, policies for management of free-ranging cat populations and regulation of pet ownership behaviours are run by animal welfare issues and not ecological impacts.

Cat owners and their perception on dangers of pet cats on the environment

There is a variation in how cats are perceived, because, despite feral cats are non-native, domestic cats are generally not characterized as an introduced species.

It is estimated that cats annually kill between 1,3 and 4,0 billion birds. This magnitude of mortality may exceed all other sources of anthropogenic mortality of birds and mammals.

A single pet cat doesn’t kill as many animals as a wild cat does to survive. But the pet’s impact happens in a much smaller area. In a given area of 100 square meters, pet cats kill between two and 10 times as many other animals as similarly sized wild predators do. Mortality rates of prey may be underestimated also because cats often harm their prey by playing with it. The prey may escape but may later fail to reproduce or die due to its wounds. Cats also indirectly affect the prey populations by disturbing the nesting birds and exerting fear and thus stress in birds.

Prevention and actions needed

The predation of wildlife by domestic cats is a complex problem. Cats are acknowledged predators of birds, herpetofauna, invertebrates and small mammals. A comprehensive understanding of this conservation issue demands an understanding of both the ecological consequence of owning a domestic cat and the attitudes of cat owners. Cat owners fail to perceive the magnitude of their cats’ impacts on wildlife and are not influenced by ecological information.

Efforts to minimise mortality from all anthropogenic threats are needed to increase sustainability of wildlife populations. While management decisions about unowned cats can be made by public authorities, the management of owned cats is primarily the responsibility of private individuals—cat owners. Simple solutions to reduce mortality caused by pets, should be implemented, such as:

  • identify cat hunting behavior as a problematic activity;
  • limiting or preventing outdoor access;
  • fitting pet and free-ranging cats with bells to reduce their success of killing birds;
  • reducing the number of cats as pets and keeping them indoors or in a fenced enclosure;
  • collaboration between veterinary, animal welfare, cat owners and conservation organizations to find and implement effective solutions;
  • micro-chipping (as has been legislated for dogs) would constitute a step towards formalising owners’ responsibilities for their cats, regardless of their whereabouts and activities;
  • taxation of ownership for each cat (as with dogs);
  • declawing, to reduce hunting success;
  • keeping the minimum number of free-raging cats on farms needed to control the rodents;
  • vaccination and sterilisation of abandoned cats to prevent the establishment of free-ranging population;
  • lethal measures to control free-ranging cat populations in locations where native wildlife conservation is of particular concern.

Conclusions

Domestic cats, particularly feral populations, are a significant threat to the already vulnerable wildlife. There is widespread acceptance of roaming cats in gardens and public spaces. Greater collaboration between welfare, veterinary and conservation organizations would help identify constructive and practical measures that owners can take to reduce the risk domestic cats pose to vulnerable wildlife.

Globally, cats are responsible for killing a range of native wildlife including herpetofauna, invertebrates, birds and small mammals, many of which are endangered. In contrast to natural predators, domestic cats are not reliant on prey to acquire their daily energy demands and can be present in densities far higher than the natural carrying capacity of their environment because they are provided with food.

Consensus shows that cats are invasive species that impact wildlife and human health. Estimating cats annually kill billions of birds and mammals. An estimate of bird mortality far exceeds any previously estimated number for cats, as well as estimates for any other direct source of anthropogenic mortality, including collisions with windows, buildings, communication towers, vehicles and pesticide poisoning.  Available evidence suggests that mortality from cat predation is substantial in all parts of the world where free-ranging cats occur.

Cats may provide benefit by killing rodents, especially in rural areas. But mostly, they threaten local bird populations in urban areas, particularly birds present in gardens. Most birds were taken by cats in the morning and mammals in the evening. So, keeping cats indoors in the morning would reduce their impact on bird populations and letting them out in the evening might increase their predation rate on pest animals, such as mice and rats.

Cats are incredible beings, even the domesticated cats. Please, for their sake and for the sake of the environment, be responsible owners and keep them indoors.

If you find this article interesting and would like some further insight, I recommend the book The Devastating Consequences of cats. In this book, the authors provide a detailed examination of the threats to global biodiversity, the environment and public health posed by free-ranging cats. They describe many scientific studies that use population modelling, feline diseases and extinctions. It examines this complex global issue and proposes scientifically sound real-world solutions to this problem. It makes a powerful case for the containment and management of free-ranging cats from both animal welfare and wildlife protection perspectives.

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