A national advocacy organization has criticized our recent story on PBS NewsHour about the shortfalls of controlling the nation’s estimated 80 million feral cats through a method called trap-neuter-return.

The statement from Alley Cat Allies says the piece “gives incomplete information about how successful this approach has proven to be.”

The success stories the group references involve small numbers of cats living in colonies. And while there is some evidence that trap-neuter-return – commonly known by its initials, TNR – has helped reduce the size of small cat populations, the outcomes have been mixed. As our story reported, some efforts succeed, while others do not.

While organizations such as PetSmart Charities have tried to implement TNR on a larger level, the effectiveness of these programs has not been established in peer-reviewed publications.

Our reporting also found that when researchers attempted to scale up these programs to control cat populations at the city and county level, the results did not hold up. The only peer-reviewed research that examines two highly regarded, large-scale TNR projects has found that the approach did not lead to a reduction in the cat population in their respective counties.

As California State University, Sacramento, population biologist Patrick Foley says in our story, cats just reproduce too quickly.

According to Foley’s calculations, Operation Catnip, run by America’s preeminent feral cat researcher and staffed by a large cadre of volunteers, would have to spay about 75 percent of the female cats in the county to successfully reduce the stray and feral cat population. That’s roughly 10 times the number the group is able to do right now.

Alley Cat Allies concludes its statement by saying that as animal advocates, its members do not believe that killing one species is the answer to saving another. While lethal control largely has been accepted in the U.S. as an effective population management tool for other so-called invasive species such as Burmese pythons and feral pigs, the large-scale euthanasia of cats is anathema to many Americans.

Our story acknowledged that stance, concluding that dealing with feral cats is not about just science, but also about our emotions.