“Effect of high-impact targeted trap-neuter-return and adoption of community cats on cat intake to a shelter,” published in The Veterinary Journal, 2014. Complete article available (open access) online here.
This study presents the results of a two-year trap-neuter-return (TNR) program conducted in a “target” zip code in Florida’s Alachua County  . Following targeted TNR efforts, researchers reported that per-capita shelter intake of cats from the rest of the county was 3.5 times higher than from the target zip code and per-capita shelter killing was 17.5 times higher.
This intensive two-year program, which delivered an estimated 57–64 TNR surgeries per 1,000 residents, resulted in a 69% reduction of per-capita feline intake from the target zip code accompanied by a 95% reduction in shelter killing of cats from this zip code. In non-target zip codes, where an estimated 14–15 TNR surgeries per 1,000 residents were delivered annually, reductions in intake and shelter killing of 12.5% and 30% were reported, respectively.
The intensive two-year program resulted in a 69% reduction of per-capita feline intake accompanied by a 95% reduction in shelter killing.
Achieving the results described above required a significant increase in targeted TNR efforts. Prior to program implementation, the target zip code had received an estimated 4–10 TNR surgeries per 1,000 residents, roughly one-quarter of the rate delivered annually during the study program.
Other studies have documented the importance of adoption to reducing free-roaming cat populations [2–4]. This study demonstrates its importance to reducing feline intake and shelter killing: 1,113 of 2,366 cats (47%) treated as part of the TNR program were either adopted directly from the program or transferred to rescue groups for adoption (79% of these were kittens under six months of age).
The demographic differences between the target and non-target zip codes are notable; median household income, for example, was $22,103 and $42,818, respectively. Forty-three percent of residents in the target zip code were living below the poverty level, compared to 24% in the non-target zip codes.
Although the researchers did not investigate the possible connections between such demographic data and shelter data, the two may be related; the target area was chosen for this study precisely because shelter cat intake in the zip code was higher than in other areas of the county.
Levy, J.K.; Isaza, N.M.; Scott, K.C. Effect of high-impact targeted trap-neuter-return and adoption of community cats on cat intake to a shelter. The Veterinary Journal 2014, 201, 269–274.
Spehar, D.D.; Wolf, P.J. An Examination of an Iconic Trap-Neuter-Return Program: The Newburyport, Massachusetts Case Study. Animals 2017, 7.
Spehar, D.D.; Wolf, P.J. A Case Study in Citizen Science: The Effectiveness of a Trap-Neuter-Return Program in a Chicago Neighborhood. Animals 2018, 7.
Spehar, D.D.; Wolf, P.J. Back to School: An Updated Evaluation of the Effectiveness of a Long-Term Trap-Neuter-Return Program on a University’s Free-Roaming Cat Population. Animals 2019, 9.