The practice of trap-neuter-release was first instituted as a means of managing feral cat populations in the United States (Jackman & Rowan, 2007). Following failure of previous attempts to reduce these colonies by culling, TNR was proposed as a more humane alternative. The reason capture-and-kill tactics were ineffective is that once a cat was captured and removed from its habitat, its territory would be available to be filled by another stray cat, and a cat from another area would move into the open “niche” (Jackman & Rowan, 2007). The logic behind TNR was to control the population by sterilizing street cats, disallowing them from reproducing while leaving their niches occupied.

While TNR was first pioneered for use on street cat populations, its application for cat colonies is a bit more contentious than it is for street dog packs. This is because the issues caused by feral cat communities are vastly different than those surrounding street dogs. While large feral dog populations pose a threat to human health, stray cats threaten natural ecosystems by decimating native prey populations (Longcore, Rich, & Sullivan, 2009).

Environmental Concerns

Because cats are descendent from predator wild cat species, their natural instinct is to hunt smaller animals for prey. Although cats have been a domestic species for centuries, they are still adept hunters and can effectively prey upon small rodent and bird populations in a variety of environments. As a result, prey species populations in areas with large feral cat communities have taken a significant hit.

Advocates for use of TNR often argue that the decline in affected native species is largely due to human encroachment on their habitat, and that cat communities cannot be blamed for this phenomenon (Longcore et al., 2009). While this is true that many factors influence native species reduction, feral cat populations associated with high human population density do contribute significantly to the decimation of local prey species.

Outdoor house cats and strays kill billions of small animals each year. Photo source: http://www.npr.org/2013/01/29/170588511/killer-kitties-cats-kill-billions-every-year

In studies performed on various counties across southern California, regions that had more free-roaming cats had greatly reduced biodiversity in wild migrant, resident, and breeding bird species (Longcore et al.). Conservationists oppose the TNR approach to handling street cats because they argue that simply “controlling” the populations is not sufficient to minimize predation on native species (Takahashi, 2014).

In Japan there is an ongoing ethical debate on the issue, as TNR seems to have little effect on the feral cat populations, which are preying on certain bird species to the point of endangerment (Takahashi, 2014). However, because a large portion of the Japanese population is Buddhist, the public is much opposed to the concept of culling, and Japanese government is scrambling to find a viable alternative (Takahashi, 2014). Recent conversation has discussed instituting mandated identification and registration of pet cats; however until all jurisdictions require these registration schemes, it is nearly impossible for the government to monitor the population and promote spay/neuter (Takahashi, 2014).