This everyday pet is a favorite in the United States. It’s also a deadly invasive species

In the United States, the domestic cat is experiencing booming popularity among pet lovers. Indeed, research shows that the proportion of American households that own a cat rose to nearly four-in-ten in 2025.

But felis catus’s growing presence in U.S. homes is not a development greeted with alacrity by wildlife conservation groups. They’re warning of the animal’s harmful effect on native species, both in America and beyond.

Cats enjoying “moment” in the U.S.

The term ‘invasive species’ - an animal or plant that harms an ecosystem not naturally its own - may more readily be associated with more eye-catching, obviously exotic animals.

For example, the Burmese python, a snake that is native to southern and eastern Asia, has become a devastatingly destructive presence in Florida since the pet trade brought it to the U.S. in the 1970s.

However, while the domestic cat is a long-established, everyday sight nationwide (and, Antarctica aside, worldwide), it also carries invasive-species status.

First domesticated in Egypt around 3,000 years ago, felis catus was introduced in America by European colonists. Fast forward to the present day, and 39% of U.S. households - some 53 million homes - had at least one pet cat in 2025, according to a study by the American Pet Products Association (APPA).

It’s a stat that led the APPA to conclude: “Cats are […] having their moment.”

Cats “make wonderful companions”, purrs the American Veterinary Medical Association (AVMA). “Their entertaining antics and affectionate behaviors have endeared them to millions of owners for thousands of years. Easily housetrained and relatively low maintenance, cats make good indoor pets and most will readily adapt to a variety of households.”

This adaptability has helped make the animal especially popular among the gen-z and millennial pet owners of today, adds the APPA: “Cats fit more seamlessly into smaller living spaces and flexible routines, making them especially appealing to younger pet parents.”

However, experts on wildlife conservation do not view the domestic cat quite so positively. So much so, in fact, that the International Union for Conservation of Nature (IUCN) has included felis catus on its list of ‘One Hundred of the World’s Worst Invasive Alien Species’.

Of notable concern is the felis catus’s impact on bird populations when it is allowed to stretch its legs outdoors.

“No greater human-caused source of direct mortality”

The domestic cat is listed on the U.S. Fish and Wildlife Service’s ‘threats to birds’ list, killing an estimated 1.4 billion to 3.7 billion each year in the States. It is a predator that has led a reported one third of the U.S.’s 800 native bird species to suffer major decline or, worse, become positively endangered.

The wildlife group American Bird Conservancy (ABC) notes that domestic cats’ prolific kill rate has made it a particular threat to the future of bird species such as the wood thrush and the least tern.

“There is no greater human-caused source of direct mortality for birds than domestic cats […] that roam outdoors,” ABC warns. “Cats’ remarkable hunting prowess comes naturally, but their introduction to new environments around the world is unnatural.”

And birds are not the only animal threatened by the free-roaming domestic cat. Globally, says the Wildlife Society, felis catus has contributed to the extinction of 63 species from multiple classes.

It is a particular menace when introduced in island habitats, “where native species have evolved in relative isolation from predators”, says the IUCN. Indeed, domestic cats are responsible for “at least 14%” of bird, mammal and reptile extinctions on islands, says the Wildlife Society.

The Wildlife Society also points to the danger domestic cats pose “as reservoirs for toxoplasmosis, bartonellosis, salmonellosis, rabies and other diseases”. For example, the body notes, the animal accounted for 19% of confirmed rabies cases in Florida in 2022.

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