As advocates for all animals, we were dismayed by the irresponsible and biased conclusions of a 2011 study on bird deaths from the Smithsonian Institution.
“Population demography of Gray Catbirds in the suburban matrix: sources, sinks and domestic cats,” published in the Journal of Ornithology1, is a limited study that cannot be extrapolated to represent the complex cat-bird dynamic nationwide. Much more disturbing, however, is how this data has been manipulated to malign cats and used widely to dredge up a false and counterproductive debate.
The Smithsonian’s Conclusions Exaggerate the Facts
The Smithsonian study relies on an extremely small sample size (just 69 birds) in a very limited radius (three sites within mere miles of each other). Opponents of Trap-Neuter-Return have already latched onto this study to clamor for cats indoors—a concept that, it is worth noting, is a death sentence for countless feral cats—but they are mishandling the data and misleading the public.
It is absurd to think that a minor study conducted on a single species of bird in a small area of suburban Maryland could accurately be used to characterize the relationship between cats and birds in landscapes all over America.
The press release circulated by the Smithsonian’s National Zoo further exaggerates and misconstrues the study’s findings, dramatically painting cats as the major threat to birds by stating that of the birds studied “almost half of the deaths were connected to domestic cats”—specifically, 47%. However, a quick look at the numbers shows this figure to be greatly manipulated:
Of the 69 birds studied, 42 died during the study. Only six of those deaths can be directly attributed to cats through observation.
The authors guessed that another three bird deaths could be attributed to cats based on circumstantial evidence.
The authors inflate the figure to 47% by focusing the discussion only on the number of birds that died due to predators, not the total number of birds in the study. They ignore the 27 birds that did not die, as well as the nine birds that died due to causes other than predation, and the 14 birds that died due to unknown predators. This leaves 19 birds that were killed by known predators.
The number of deaths attributable to cats is 9 birds out of 69—or 13%—not 47%.
But when taken as a percentage of all of the deaths from known predators, (9 out of 19) the number of birds killed by cats inflates to 47%—hyping cats’ impact on bird populations way out of proportion.
Statistics are a powerful persuasive tool because people often take them at face value, but numbers can be manipulated too. The omission of 50 birds—well more than half the sample size—in calculating this figure dramatically changes the conclusions of the study.
As the researchers themselves note, they also failed to examine whether the few deaths attributed to cats were additive—more birds dying than normal—or compensatory—consistent with the normal mortality rate for this species. Considering data from the North American Breeding Bird Survey, which shows the Maryland catbird population to be on the rise, the former seems unlikely. Cats specialize in hunting rodents; also, studies have confirmed that the birds who are caught are generally weaker animals who are not likely to have survived.
Humans are the True Threat to Birds
When rationally viewed, the Smithsonian study and the resulting press flurry has added nothing to the overall conversation about how to protect animals. Instead, it has only drawn attention away from the real threat to birds—people.
Alley Cat Allies wants what’s in the best interest of all animals, including birds. Environmental experts say we must change the way we are impacting our environment. Until we can stop going in circles, perpetuating this false debate, and focus on the real threat, we are truly just chasing our tails.
 Balogh, Anne L., Thomas B. Ryder and Peter P. Marra. Population demography of Gray Catbirds in the suburban matrix: sources, sinks and domestic cats. Journal of Ornithology. 2011. http://dx.doi.org/10.1007/s10336-011-0648-7; http://nationalzoo.si.edu/scbi/migratorybirds/science_article/pdfs/...
Thanks for this clarification.