Cats

Introduction

Cats are among the most popular type of pets, but they pose several threats to the environment and wildlife. This page focuses on some of these issues, and how to reduce the impact of cats, such as keeping them indoors, fixing them to reduce the number of homeless animals that have to be routinely euthanized around the world, and avoiding letting their waste into our sewage system where wildlife can be infected.

Population Statistics

"There are an estimated 600 million cats on the planet... experts believe that there are more cats than any other species of mammal, other than humans." - Catster

"Estimates of the number of feral and wild cats in the world vary widely, from anywhere between 30 million and 100 million animals."  - Catster

In the USA, "Of the cats entering shelters, approximately 37% are adopted, 41% are euthanized, and less than 5% of cats who came in as strays are returned to their owners." - Community Care College: Pet Facts 

Environmental Impact of Cats

Invasive Apex Predators

"Cats are apex predators that can wreak havoc on local biodiversity. Research shows that outdoor cats on islands have already caused or contributed to the extinction of an estimated 33 species. Wild cats pose an outsized threat to birds, which make up half their diet. In Hawaii, known as a bird extinction capital of the world, cats are the most devastating predators of wildlife. “We know that cats are an invasive, environmental threat,” said Lepczyk, who has published papers proposing management policies for outdoor cats." - Wired: Kitten Season Global Warming Cat Breeding 

Food Security

Food & Carbon

Kitty Litter

Mining

Water Pollution

Greenhouse Gases

Species Threatened by Cats

"A study published in April estimated that UK cats kill 160 to 270 million animals annually, a quarter of them birds. The real figure is likely to be even higher, as the study used the 2011 pet cat population of 9.5 million; it is now closer to 12 million, boosted by the pandemic pet craze. Seen alongside drops in bird numbers across the EU and the UK, it is “quite alarming”, says lead author and cat ecologist Tara Pirie from the University of Reading." - The Gaurdian

"A parliamentary report found that Australia's almost 3.8 million pet cats kill up to 390 million animals yearly and in NZ 18 million birds, bats and bugs end up killed by pet cats every year. Additionally, domestic cats may add to stray and feral cat populations – by escaping or breeding with feral cats." - Predator Free NZ

Species threatened by cats include:

Amphibians


Frogs

Bats

"Domestic cats are the most highly cited predators of bats, possibly because cats often present kills to their owners (Daniel & Williams 1984)." - Mammal Review: The Threat of Invasive Species to Bats (PDF)

Birds

Cats are one of the greatest threats to birds and other small animals world wide, after being introduced by humans. Similarly rats and mice often destroy nests of ground-nesting bird species (particularly on islands and places in Oceana where they didn't evolve alone side these introduced pests).

Each year, cats cause around 1 to 4 billion bird deaths in the US alone.  - BirdFact

Ground-Nesting Birds

Ground-nesting birds, including those referred to as "game birds", kiwi birds, and many island birds have evolved to build their nests on the ground, making them unfortunately easy targets for predators like invasive cat and rat, which where imported (sometimes by accident) to new ecosystems.

Hummingbirds


Insects

Koalas


Marine Mammals

Otters

"Scientists in California are raising the alarm after four sea otters were killed by an unusual strain of a common parasite spread by cats, a concerning but preliminary finding that researchers told Forbes signals a potential health threat to other animals prone to infection, including humans."

Fish

Cat waste can impact fish and other creatures in aquatic environments. This is can be caused by run off from people's garden (when cats are allowed outside), or through sewage systems if people flush kitty litter.

Any impact on fish populations can in turn effect their natural predators, including marine mammals.

"Toxoplasma is a ubiquitous parasite. It is “very good at spreading itself around in the environment and exploiting new habitats and new hosts,” Miller told Forbes, adding that “it is considered one of the most globally successful parasites for this reason.” It passes into aquatic ecosystems in water runoff and is often concentrated in marine invertebrates like shellfish. Around 11% of people in the U.S. ages 6 years and older have been infected with Toxoplasma, the CDC estimates, a figure that rises as high as 60% in some parts of the world. Human infections can persist for a long time, possibly for life, but most are kept in check by the immune system and the majority are completely unaware of their infection. Symptoms vary and can range from flu-like symptoms to severe damage to the eyes, brain and other organs and, in some instances, death. Unborn children are particularly vulnerable and infection can trigger premature birth and a number of health issues. Cats are a vital part of the parasite’s life cycle and it’s shed in their feces (which is why pregnant people are advised against changing litter trays). Infections are also reported to change hosts’ behavior—infected rats are attracted to cat urine—and in humans infections are linked to higher rates of suicide, rage, traffic accidents and schizophrenia." - Forbes: Researchers Warn Cat Poop Parasite Killing Otters in California Could Pose Human Health Threat 

Reptiles

Lizards


Rodents

Ways to Reduce the Environmental Impacts of Cats

Keep Cats Indoors

This is the only effective way to keep cats from hunting and killing wildlife. 

Problems with Cat Collars

Some people think it's OK to put collars with bells onto cats, but these can accidentally entangle on plants or fencing and strangle the cat. Break-away collars can break away too easily, leaving a trail of plastic each time the cat is fitted with a collar and then breaks out of it.

Another problem is that the bells can give the cats away to larger predators including dogs.

Cat Litter

NEVER flush kitty litter down the toilet! Our septic systems are not equipped to remove Toxoplasma, which endangers both humans and wildlife when the contaminated waste water makes contact later in the water cycle. Kitty litter needs to be properly disposed of in landfills, since most communities don't have any system that properly treats cat waste.

Standard kitty litter has a surprisingly big environmental impact, but you can reduce this by switching to eco-friendly versions, including newspaper pellets, and agricultural waste. You can even recycle at home to make your own kitty litter.

Planet-Friendly Diet

"Pet guardians have been keen to adopt vegan pet diets. The BVA noted that 42% of companion animal vets reported they had clients who feed meat-free diets. The switch to such diets is being driven by concerns about the health, environmental, and food animal welfare impacts of meat-based diets. Considering pet health, by mid 2024, 10 studies in dogs and three in cats had demonstrated equivalent or superior health outcomes using (nutritionally-sound) vegan or vegetarian diets. These included large-scale studies, studies using veterinary clinical examinations, diagnostic tests and laboratory data, and studies reporting veterinary health assessments, as well as owner opinions (which were recently found to be uninfluenced by diet choice, also increasing confidence in their reliability).

When considering environmental benefits, the key study in this field recently found that a global transition toward nutritionally-sound vegan diets for the 471 million pet dogs and 373 million pet cats owned worldwide in 2018, would provide major environmental benefits. If all pet dogs were transitioned, it would save more greenhouse gases than produced by the entire UK. If all pet cats were transitioned, sufficient food energy could be saved to feed 70 million people - more the entire UK population. Transitioning pet dogs would allow 450 million people to be fed - greater than the entire EU population. And around seven billion farmed land animals would be spared from slaughter annually, or 9% of the global total, with significantly higher proportions in countries with high pet ownership, such as the UK or US." - Access Wire: British Veterinary Association Ends Opposition to Vegan Diets for Dogs 

Resources & Guides

International

Organizations

International

Europe

UK

North America

Canada

USA

Oceana

Australia