In case it slipped under your radar this week, an estimate of the number of birds killed annually by cats in Canada was released, and it is no Far Side cartoon.
In a special issue of Avian Conservation and Ecology (an open-access journal sponsored by the Society of Canadian Ornithologists and Bird Studies Canada), scientists tackled quantifying “Human-related Mortality of Birds in Canada“. When all research teams had weighed in, and all the scientific votes were cast, “death by cat” came in at the top – and we’re talking penthouse vs. lobby here (see Figure 1: “Bird Deaths in Canada”; presented in a recent Ottawa Citizen article by Tom Spears).
In fact, this graphic is likely quite kind: splitting domestic and feral cats into two categories makes the figure appear as if other sources of human-related mortality are somewhat close in impact to cats, but see Figure 2 below. What the research suggests is that of approximately 268 million birds killed annually via anthropogenic activity, approximately 196 million are killed by either domestic or feral cats - that’s 73%.
Furthermore, estimates of direct mortality by cats do not account for sublethal and indirect effects of cats on bird populations such as reduced parental care and attraction of other nest predators when cats are lurking, and mortality of rodents and other organisms that are prey for some bird species.
A figure like 73% is relatively easy to grasp – nearly 3 out of every 4 birds killed by human-related causes is via cats – but what about 196 million, is that a significant number of birds? How do we place that in context? The author, Peter Blancher, suggests that cats annually kill 2-7% of the roughly 5.2 billion birds breeding in southern Canada (where most Canadians live). Viewed in the light of estimated population sizes of Canadian birds (derived from the Partners in Flight Population Estimates Database), 196 million annual bird mortalities is equivalent to nation-wide populations of:
- White-throated Sparrows (130 million) + Song Sparrows (60 million), or
- American Robins (140 million) + Black-capped Chickadees (20 million) + Cedar Waxwings (30 million), or
- Barn Swallows (5 million) + Chestnut-sided Warblers (13 million) + Gray Catbirds (3.6 million) + MacGillivray’s Warblers (7 million) + Dark-eyed Juncos (130 million) + Northern Cardinals (0.5 million) + …