Position of the American Society of Mammalogists on Trap-Neuter-Release (Return) of Feral Cats—approved June 2010
Trap–Neuter–Release (TNR) programs in which feral cats (Felis catus) are sterilized and then released back into the environment have been proposed as a non-lethal alternative to control feral populations of this predator and to lessen their environmental impact. TNR programs have been adopted or tacitly allowed by a number of metropolitan areas in the US, despite lack of evidence of their efficacy and despite accumulation of data confirming the negative effect of free-ranging cats on birds and mammals.
As mesocarnivores, domestic cats commonly prey upon native vertebrates, including mammals. Whereas predators are normally in low abundance in natural communities, feral populations of cats are frequently maintained at high levels through recruitment from human-maintained sources and through food subsidies. Although feeding feral cats lessens their dependence on predation, it does not necessarily lessen their frequency of predation.
Cats have been implicated in population decreases of mammals, birds, and reptiles on islands, as well as in mainland communities. Further, fragmentation of natural environments through agriculture and urbanization results in mammalian assemblages that more closely resemble insular than continental communities, which magnifies the impact of subsidized predators on natural populations. In addition to their direct impact through predation, feral cats are sources of parasites and diseases transmissible to humans, livestock, pets, and native populations.
It is the position of the American Society of Mammalogists that maintenance of high populations of these non-native predators through TNR or similar programs, or by subsidizing feral populations with supplemental food, is extremely detrimental to native mammalian assemblages. The American Society of Mammalogists strongly opposes TNR and urges municipalities to ban use of such programs and to prohibit feeding of feral cats. We further encourage effective measures to reduce or eliminate feral populations of these introduced predators.