Nature Communications, a journal dedicated to publishing research in the biological, physical and chemical sciences released a report on January 29th, on the findings of a combined Smithsonian Conservation Biology Institute and Fish and Wildlife Service study. The results quickly became fodder for an uncritical media willing to accept its questionable claims.
It is important to understand that this report does not rely on new research but a re-interpretation of previously published research. Although the authors claim their publication is a “systematic review,” the paper does not meet the standards for meta-analysis or systematic review. For example, the authors do not score the quality of the previous research they assessed or define the number of animals extrapolated in each paper. There is no correction factor to correlate the environments studied (urban vs. rural) with the actual land mass distribution of the US. Some of the papers cited simply restate or exaggerate data from other papers, so they are not even analyzing original data as meta-analysis/systematic review standards require.
Sadly, there won't be much opportunity for critical analysis because the authors elected to place their “results” in the mainstream media rather than submitting them for peer review. Clearly, this report was not written for scientists; it was written to misinform policy makers and the media.
The study claims domestic cats in the United States kill a median of 2.4 billion birds and 12.3 billion mammals a year, most of them native mammals like shrews, chipmunks and voles rather than introduced pests like the Norway rat.
This estimate is two to four times higher than mortality figures previously bandied about, making the domestic cat the single greatest human-linked threat to wildlife in the nation – greater than automobiles, pesticides and poisons, collisions with skyscrapers and windmills and other so-called anthropogenic causes.
The results admittedly come with wide ranges and uncertainties but seem purposely designed to fuel the sometimes vitriolic debate between environmentalists who see free-roaming domestic cats as an invasive species and animal welfare advocates who are appalled by the millions of cats (and dogs) euthanized in animal shelters each year.
Both sides do agree on two points; pet cats should not be allowed to prowl the neighborhood at will, any more than a dog, horse or potbellied pig, and cat owners who insist that their felines "deserve" a bit of freedom are both irresponsible and are not cat friendly.
Recent projects like Kitty Cams at the University of Georgia, in which cameras are attached to the collars of indoor-outdoor pet cats to track their activities filmed cats not only preying on cardinals, frogs and field mice but also lapping up antifreeze and sewer sludge, dodging moving cars and sparring violently with large dogs.
These are some of the reasons animal advocates claim that it is inhumane to let pet cats roam freely outdoors.
The study takes lethal aim at feral cats, however, calling into question the efficacy of the Trap-Neuter-Return (TNR) methodology for controlling and decreasing feral cat populations. TNR is the practice of trapping, spaying and returning un-owned cats to a managed outdoor colony in the area from which they came. What the authors of the report failed to understand is that TNR is the only possible means for reducing the number of wildlife killed by feral cats.
Although some communities try to employ eradication as a remedy, decades of such efforts across the United States has irrefutably demonstrated eradication does not work.
Feral cats have a strong biological survival drive; attempts to catch cats for extermination triggers two biological imperatives causing the surviving cats to both over-breed and over-produce. That is, instead of having one litter of two to three kittens per year, a stressed female will have two or three litters of six to nine kittens annually.
Even if a community could catch and remove all their feral cats, a phenomenon called "the vacuum effect" quickly resul