Many of the opponents of Trap-Neuter-Return (TNR) suggest that stray, abandoned, and feral cats (a population increasingly referred to collectively as "community cats") pose a significant risk to wildlife populations - birds, in particular - as well as to public health. But these claims are grossly exaggerated, and the supporting science is badly flawed.
In a recent New York Times op-ed, Richard Conniff refers to a 2013 paper, for example, describing the results of computer modeling conducted by researchers at the Smithsonian Conservation Biology Institute and U.S. Fish and Wildlife Service, as evidence that outdoor cats take "a substantial bite out of the total bird population." In fact, the enormous size of that alleged bite should have tipped Conniff off that something wasn't right about the work. Indeed, to those of us familiar with the issue, it's clear that this paper was little more than an agenda-driven (and publicly funded) attempt to undermine TNR and community cat programs.
There is simply no evidence, other than in some island contexts, to suggest that cats are having a negative impact on wildlife populations.
The public is simply fed up with a lethal approach that for generations has proven costly and ineffective. You'd think, given the way TNR opponents try to frame the issue, that communities across the country have been successful in managing their population of unowned free-roaming cats through "traditional" methods; in fact, no community has killed its way out of the "feral cat problem."
Even a cursory look at successful eradication efforts makes it clear why that's the case.
On barren, uninhabited Marion Island, for example - which, at 115 square miles, is the largest island from which cats have been eradicated - it took 19 years to exterminate approximately 2,200 cats - using feline distemper, poisoning, hunting and trapping, and dogs. On Ascension Island - just 34 square miles - it cost nearly $2,200 (in 2013 dollars) for each of the 635 cats eradicated over 27 months (nearly 40 percent of which were pets).
Is it any wonder Conniff and others opposed to TNR never mention these well-documented "successes"?
There's plenty of evidence that TNR can be effective and stabilizing and reducing the number of a cats in a given colony or area. In particular:
- A TNR program on the campus of the University of Central Florida that began in 1991 led to the adoption of nearly half of the 155 cats living on campus over an 11-year observation period. In 2002, upon completion of a related six-year study, just 23 cats remained on campus.
- Rome, Italy, 2000 to 2001: A survey of caretakers (103 cat colonies) revealed a 22 percent decrease overall in the number of cats despite a 21 percent rate of "cat immigration." Although some colonies experienced initial increases, numbers began to decrease significantly after three years of TNR: "colonies neutered 3, 4, 5 or 6 years before the survey showed progressive decreases of 16, 29, 28 and 32 percent, respectively."
- Randolph County, NC, 1998 to 2005: 36 percent average decrease among six sterilized colonies in the first two years; three unsterilized colonies experienced an average 47 percent increase over the same period. Four-year follow-up census: one colony reduced from 10 cats to none; at seven years, another colony originally containing 10 cats had been reduced to one cat. 
- In December of 2009, the last of the Newburyport, Massachusetts, "wharf cats" died. According to both Alley Cat Allies and the local paper, this colony once included something like 300 cats. A 1996 story in the Boston Herald describes "an estimated 200 wild, roaming cats."  (Zorro, the last of the colony cats, was 16 years old.)
Now, let's just consider that Randolph County example. Some TNR opponents would argue that a 36 percent decrease over two years is insufficient. But, I've yet to hear of a community demonstrating such a decrease using lethal methods.
In addition to its most obvious benefit - sterilization - TNR offers a number of benefits to both the cats and the community. In many programs, cats are vaccinated against rabies before being returned to their "outdoor homes." (Such vaccinations are, to my knowledge, standard practice in parts of the country where rabies has been spread from wildlife species to cats.)
It's become increasingly clear in recent years that, in many communities, the single greatest threat to cats - unowned and owned alike - is the local shelter. More than half of the cats brought into U.S. shelters are killed there.
This, thankfully, is changing. (See, for example, this recent op-ed about the program Best Friends Animal Society involved with in Albuquerque.)
In communities where a trip to the shelter is still likely to prove fatal, however, community cat programs (reliant upon TNR) provide the best possible outcome for the vast majority of cats. It's clear from our experience, and that of others involved with such programs, that most outdoor cats are thriving in their environment.
TNR is, like so many other aspects of the animal welfare movement, a compromise. In most instances, though, it's the best option we've got.
[1.] Nutter, F.B., Evaluation of a Trap-Neuter-Return Management Program for Feral Cat Colonies: Population Dynamics, Home Ranges, and Potentially Zoonotic Diseases, in Comparative Biomedical Department2005, North Carolina State University: Raleigh, NC. p. 224.
[2.] Donlan, A.E., North Shore cat-lovers go... Where the wild things are, in Boston Herald1996: Boston, MA.