Pet and feral cats kill an estimated 4 billion birds in North America every year, according to a new Canadian study and recent Smithsonian survey, both of which are fueling calls to exterminate feral cat colonies throughout the nation's big cities.

The studies are proof that domestic cats, both house trained and feral, pose a huge threat to the continent's bird population, according to the Washington-based American Bird Conservancy, which tipped Secrets off to the dual surveys.

They are a “warning trend about this growing invasive species disaster that is at our doorstep in the form of outdoor cats,” said Grant Sizemore, “cats indoors” program manager for the nation’s leading bird conservation group.

In Canada, the new report from the National Wildlife Research Centre puts their cat kill at up to 350 million birds annually. In just the southern section of Canada, cats dine on up to 7 percent of the bird population.

Surveys released this year in the United States, most notably Smithsonian's, estimate that the 160 million cats kill 2.4-4 billion birds in the U.S. every year and about 20 billion mammals like mice.

The studies are expected to be used to bolster efforts in some cities and states to manage or eliminate feral cat populations, both for the health of cats and survival of birds.

“Cats on the streets lead harsh and traumatic lives,” said Sizemore.

He said that the American Veterinary Medical Association found that feral cats live an average of just two years compared to house cats which average 10 years. The group opposes efforts to trap and move the cats and encourages the “humane elimination” of feral cat colonies. But other groups such as People for the Ethical Treatment of Animals are fighting that plan.

Paul Bedard, The Washington Examiner's "Washington Secrets" columnist, can be contacted at