Canada’s national environmental agency has determined that domestic cats — pets and free-roaming strays — are the most lethal threat to birds in the country.
Environment Canada conducted a series of unprecedented studies that looked at more than 25 sources of human-caused bird mortality and published its findings in a special issue of the online journal Avian Conservation and Ecology last September.
Cats kill 100-350 million birds in Canada annually, researchers say. The median estimate of cat-caused mortality — almost 200 million bird deaths per year — was about eight times greater than the 25 million deaths caused by collisions with power lines, the second leading cause of mortality. The third highest cause — collisions with structures — accounted for about 25 million bird deaths per year.
The results echo the findings of an earlier study on cat predation in the United States. Scientists from the Smithsonian Conservation Biology Institute and the U.S. Fish and Wildlife Service estimated in a January 2013 report in Nature Communications that 114-164 million feral and pet cats in the U.S. are responsible for the deaths of 1.4-3.7 billion birds and 6.9-20.7 billion mammals every year.
Peter Blancher, author of the paper on cat predation in Canada, notes that the population of feral cats in the U.S. is 7 to 19 times greater than that in Canada. The difference, he says, means that cats kill at least 10 times more birds south of the border.
Taken together, the studies estimate that cats kill 1.5-4 billion birds in the U.S. and Canada — a source of human-related bird mortality that is far greater than collisions with windows, buildings, communication towers, and other causes.
“Available evidence,” write Smithsonian research scientist Scott Loss and his colleagues, “suggests that mortality from cat predation is likely to be substantial in all parts of the world where free-ranging cats occur.”
This article appeared in the February 2014 issue of BirdWatching Magazine.