Effect of a long-term trap-neuter-return and adoption program on a free-roaming cat population

Levy, Gale and Gale conducted one of the most-cited long-term evaluations of trap-neuter-return, following a managed free-roaming cat population on a university campus over more than a decade. Cats were trapped, sterilized, vaccinated and returned, with adoptable individuals removed for rehoming. Over the study, the population declined substantially, attributed to a combination of sterilization, adoption and emigration, and no kittens were born in the colony in later years once a high proportion were neutered. The authors concluded that intensive TNR combined with adoption can reduce colony size over time, though they noted the importance of preventing immigration and abandonment of new cats. The study became a foundational reference in debates over whether TNR can effectively manage free-roaming cat populations and under what conditions.