House cats: The destructive invasive species purring on your lap

There is an invasive species in the United States responsible for the deaths of an estimated 14.7 billion birds and mammals each year. If that's not shocking enough, consider this: There's a good chance that one of these invaders is living in your house.

Another in a long line of scientific studies documenting the impact of outdoor cats on our natural environment has just been released, bringing national attention again to the issue. This study was published in Nature Communications and authored by scientists from the Smithsonian Conservation Biology Institute and U.S. Fish and Wildlife Service.


Another study, published in the peer-reviewed public health journal Zoonoses and Public Health, found that free-roaming cats also pose a threat from "serious public health diseases" to humans, domestic animals and wildlife. The study came from scientists at the University of Tennessee and a retired scientist from the California Department of Fish and Game. Among the key findings of that paper:

•Free-roaming cats are an important source of animal-transmitted, serious diseases such as rabies, toxoplasmosis, and plague;


•Free-roaming cats account for the most cases of human rabies exposure among domestic animals, and are the source for one-third of rabies post-exposure treatments in the United States (because of inconsistent incident reporting, that number is likely an underestimate of the actual cases of rabies exposure);

•Trap, neuter and release programs may lead to increased, uninoculated populations of cats that can serve as a source of transmittable, serious diseases.

The study also noted that since 1988, rabies has been detected more frequently in cats than in dogs; in 2008, the number of cats detected with rabies was four times higher than dogs. In 2010, rabies cases declined for all domestic animals except cats.

A different study on the effects of urbanization on wildlife that tracked the early lives of gray catbirds in three areas of Washington, D.C.'s Maryland suburbs found that outdoor cats were the top source of known predation on the young birds. The study, by scientists from SCBI and Towson University, published in the Journal of Ornithology, found that almost 80 percent of the catbird mortality in the study was from predation and that cats were the source of almost half of the known predation.

On top of that, a University of Georgia study announced this past summer found that outdoor cats that killed did so once every 17 hours. The study authors attached small video cameras to 60 outdoor domestic cats in the city of Athens, Ga., and recorded their outdoor activities during all four seasons.

These recent studies and dozens more from years past, originating from highly esteemed organizations, lay to rest any argument as to whether or not outdoor cats inflict great damage on native wildlife. They demand from the public a serious look at how we can protect biodiversity from this introduced predator.

The only sure way to protect wildlife, cats and people is for domestic cats to be permanently removed from the outdoor environment. Trap-neuter-release programs that perpetuate the slaughter of wildlife and encourage the dumping of unwanted cats is a failed strategy being implemented across the United States without any consideration for environmental, human health, or animal welfare effects. It can no longer be tolerated.

Local governments need to act swiftly and decisively to gather the 30 million to 80 million unowned cats, aggressively seek adoptions, and establish sanctuaries for or euthanize those cats that are not adoptable. Furthermore, pet cats should be spayed/neutered and kept indoors. For their own safety, owned cats need to be licensed and microchipped.


Any notion that cats need "outdoor time" flies in the face of reality. Outdoor cats live about one-third as long as indoor cats, owing to their exposure to a variety of diseases, parasites and toxins, as well as to their predictable run-ins with dogs, other cats, foxes, coyotes, vehicles and, of course, abusive people.

Only through proper identification can lost cats be consistently returned to their homes, and no owners need worry about accidental adoption or euthanasia of their beloved companion. It is also time to treat cat owners as we treat dog owners by enforcing anti-abandonment laws and requiring leashes or enclosures for cats outdoors. Such an approach is better for cats, better for birds and better for people.

George Fenwick, president of the American Bird Conservancy, received a Ph.D. in pathobiology at the Johns Hopkins University, studying the effects of alien species on native birds.