Reduction of free-roaming cat population requires high-intensity neutering in spatial contiguity to mitigate compensatory effects.

When free-roaming in natural areas, the domestic cat (Felis silvestris catus) is ranked high among the most destructive alien species. Near human dwellings, it might pose a risk to humans, impair sanitation, and suffer from poor welfare. Cats' popularity as companion animals complicates their population control. Thus, culling is often replaced by a fertility control method called "trap­neuter­return/release" (TNR), considered more humane. Despite the extensive application of TNR, a long-term controlled study was never performed to test its effectiveness. We present a uniquely designed controlled field experiment for examining TNR effectiveness. The study was performed over a 12-y period, divided into preintervention and mixed- and full-intervention phases, and spanned a 20-km2 urban area. Trends of cat, intact-female, and kitten counts, cat reproduction, and carcass reports were compared among study phases and areas with different neutering intensities. The cat population increased during the first two study phases and did not decline in highly neutered populations, presumably due to cat immigration. Expansion of high-intensity neutering to the entire city in the full-intervention phase (>70% neutering percentage) reversed cat population growth, reaching an annual approximately 7% reduction. This population reduction was limited by a rebound increase in cat reproduction and longevity. We conclude that cat population management by TNR should be performed with high intensity, continuously, and in geographic contiguity to enable population reduction. To enhance management effectiveness and mitigate compensatory effects, we recommend further evaluating an integrated strategy that combines TNR with complementary methods (e.g., vital resource regulation, ill cat euthanasia, and adoption).

An accessible scheme for monitoring free-roaming cat population trends.

Free-roaming cats (FRCs) form nondomiciliary population groups that might lead to adverse environmental effects, as well as to welfare impairment of the cats themselves. Though criticized by ecologists, for the last two decades, the trap-neuter-return (TNR) programs were often employed aiming to manage these populations. At present, no accepted and accessible monitoring scheme exists to determine the effectiveness of those programs. In the current study, we present the reliability and validity of an applicable monitoring scheme, as an adjunct tool for a TNR program of FRC in an urban environment. The monitoring scheme is based on cat observation counts along randomly chosen transects. Fifty-four transects were repeatedly walked for three years, between 2012-2014, in 27 neighborhoods within an urban area of 19.3 Km2. Cat numbers counted in the 2014 observations were significantly higher than cat numbers found in the 2012 observations (prevalence ratio = 1.258, CI95%= 1.198-1.322, p < 0.001). The method revealed high reliability when different observers and different transects in the same neighborhood were compared (R 2 = 0.548 and R 2 = 0.391, respectively, for measuring cat counts per km, p < 0.001; and R 2 = 0.5 and R 2 = 0.74, respectively, for measuring neutering percentage, p < 0.001). This scheme was constructively validated by measurements of municipal data on the number of neutered cats and demonstrated high correlation (R 2 = 0.59, p < 0.001). Conducting cat observations using friendly calling and feeding resulted in an increased number of FRC observed per km walk (by 79% and 22%-30%, respectively). However, these manipulations did not alter the recorded percentage of neutered cats. The proposed scheme provides spatio-temporal data that can contribute to the management programs of such cat metapopulations in an urban environment.