BOOKS: The State of Canada’s Birds 2012
From ANIMAL PEOPLE, September 2013: (Actually published on October 8, 2013)
By the North American Bird Conservation Initiative (NABCI-Canada), under the leadership of Environment Canada, Bird Studies Canada, Ducks Unlimited Canada, Nature Canada, the Nature Conservancy of Canada and Wildlife Habitat Canada | Free download: www.stateofcanadasbirds.org and Avian Conservation & Ecology 8(2). Free download: www.ace-eco.org/vol8/iss2/art1
Alleged an October 1, 2013 media release from the American Bird Conservancy, “A new study from the government of Canada that looked at more than 25 human-caused sources of bird mortality has found that domestic cats, both feral and owned, are the leading lethal threat to birds in the country.”
The ABC media release referenced The State of Canada’s Birds 2012, published in July 2012, and the supporting studies of bird mortality published in the October 2013 edition of the journal Avian Conservation and Ecology––and those studies, read as a whole, say no such thing.
The focal finding of The State of Canada’s Birds 2012 is that “On average, Canadian breeding bird populations have decreased 12% since 1970, when effective monitoring began for most species. For species with sufficient data to monitor their status, 44% have decreased, 33% have increased, and 23% have shown little overall change. Some groups, such as grassland birds, aerial insectivores, and shorebirds, are showing major declines. Other groups such as waterfowl, raptors, and colonial seabirds are increasing, due to careful management, changes in habitat, and reductions of environmental contaminants.”
Of the bird groups in decline, grassland birds usually dwell in rural areas far from most cars; aerial insectivores tend to come within range of cat predation only when ill or injured; and much Canadian shorebird habitat is on rocky islands, in swampy estuaries, and/or in the Far North, not easily accessible to cats.
Summarizing research into the major causes of Canadian bird declines in just 36 pages, The State of Canada’s Birds 2012 devotes more than 28 pages to habitat issues, mentions cats in just three sentences on page 29, stating the “Outdoor cats kill more than 100 million birds every year in Canada,” and concludes with discussion of research methods and acknowledgements.
One hundred million birds per year is a toll close to the 125 million birds per year that U.S. Fish & Wildlife Service researcher Albert Manville attributed to cats in the U.S. in 2003, when the U.S. cat population was near the all-time peak of about 100 million total cats, 18% more than today, according to the American Veterinary Medical Association U.S. Pet Ownership & Demographics Sourcebook, 2012 edition.
And there are only about 8.5 million pet cats in Canada, plus 1.2 to 4.2 million feral cats, according to the input data assembled by Peter Blancher of Environment Canada. Much of the input data is projected from studies done in the U.S., and in some instances, done on other continents.
Admits Blancher in his first paragraph, “Reliability of the total kill estimate would be improved most by better knowledge of feral cat numbers and diet in Canada, though any data on birds killed by cats in Canada would be helpful.”
Time and again Blancher acknowledges the shortcomings of his inputs––e.g., “The majority of studies relied on for predation rate of feral cats are over 50 years old and so may not represent the types of landscapes in which feral cats are most found today, in Canada or elsewhere,” he writes.
But Blancher makes a credible effort to adjust the information from other times and places to accurately represent what might happen when findings from elsewhere are projected into the Canadian climate and habitats. The weaknesses in Blancher’s work are primarily the weaknesses of the studies done by others, some of them known for considerable exaggeration and anti-cat bias. Blancher might, for example, have included a disclaimer in using research by former Smithsonian Institution ornithologist Nico Dauphine––the very first source he cites––to acknowledge that Dauphine was convicted in 2011 of trying to poison cats; the conviction was upheld in August 2013 by the Washington D.C. Court of Appeals.
Blancher concludes that “Despite a dearth of Canadian data on predation by cats, it is clear from the numbers of house cats in Canada and predation rates elsewhere that the number of birds killed by cats each year is very large, probably the largest human-related source of bird mortality in Canada.” But even 100 million birds per year killed by cats would be minor losses compared to Blancher’s 2002 finding that five billion birds from over 400 species breed each year in Canada, and his conclusion as to the significance of cat predation is not well supported by the other papers presented in Avian Conservation and Ecology 8.2.
Guest editors Travis Longcore and Paul A. Smith in their introduction, “On Avian Mortality Associated with Human Activities,” mention cats only once, in passing, while cautioning that “the effects of a single stressor are almost impossible to parse unless the focus population is spatially restricted or extraordinarily well monitored,” and that “The effects of human-related mortality on bird populations will differ depending on whether mortality is additive to natural mortality or compensatory,” meaning that one cause of death displaces another.
Most predation, including by cats, is compensatory: predators typically hunt the sick, the injured, the old, and the least viable young of their prey species.
Independent researcher Sébastien Rioux and Jean-Pierre Savard and Alyssa Gerick of Environment Canada offer that collisions with electrical transmission lines may kill anywhere from 2.5 million to 25 million Canadian birds per year. Christine A. Bishop of Environment Canada and Jason M. Brogan of Simon Fraser University project that vehicular collisions kill about 13.8 million birds per year in Canada. A trio of researchers sets the probable Canadian toll from bird collisions with windows at only 100,000 per year.
“In total,” seven co-authors conclude in the last paper of the collection, A Synthesis of Human-related Avian Mortality in Canada, “we estimate that approximately 269 million birds and two million nests are destroyed annually in Canada, the equivalent of over 186 million breeding individuals. Combined, cat predation and collisions with windows, vehicles, and transmission lines cause more than 95% of all mortality.” But no data is included about the probable effects of pesticides on bird mortality, in part because pesticide intoxication often does not kill birds outright, and is therefore among the most difficult sources of mortality to quantify. Instead, intoxication––like disease––tends to make birds more vulnerable to collisions, predation, and landing in inappropriate places.
“Recent evidence indicates potentially important population-level effects of rodenticides on birds of prey, but this source of mortality was not considered here,” the co-authors acknowledge.
In addition, they write, “We were unable to include several additional sources of human-related mortality that may be important to Canadian bird populations.” Among these are livestock impacts “such as vegetation management and negative effects of trampling on bird nests,” “mortality and nest destruction from forest harvesting on private lands,” aircraft strikes, birds landing in lethal tailings ponds, and aquaculture.
The co-authors believe “The number of birds killed annually by these sources is expected to be small.” What is large, though, is that “avian mortality represents only a portion of the overall impact to avifauna” as result of human activity.”
The Synthesis of Human-related Avian Mortality in Canada co-authors tip-toe carefully around human-influenced climate change, the existence of which is denied by Canadian prime minister Stephen Harper and his minions. But they recommend that “indirect effects such as habitat fragmentation and alteration, site avoidance, disturbance, and related issues must also be carefully considered,” if bird populations are to be effectively conserved. Merely blaming cats, cars, power lines, or any other obvious source of dead birds does not explain the population losses of the past 40-odd years.