In a study looking at one zip code in a Florida community with high impoundments of community (unowned) cats, the answer was yes.
The two-year program was designed to trap and alter a minimum of half the cats in one zip code; the cats were neutered and either adopted or returned to the community. A program of counseling to help community members with nuisance issues was also implemented in the target zip code as part of the study.
A total of 2,366 cats were trapped and altered from that zip code. Shelter cat intake was then compared between that zip code and the rest of the county.
Shelter cat intake in the un-targeted parts of the county decreased by 66 percent during the study period, but only decreased by 12 percent in the non-target area. The number of cats who lost their lives in the shelter was 17.5-fold higher in the un-targeted areas.
The study's authors concluded, "High-impact TNR combined with the adoption of socialized cats and nuisance resolution counseling for residents is an effective tool for reducing shelter cat intake."
The complete study is available at the link below.
J.K. Levy, N.M. Isaza, K.C. Scott, Effect of high-impact targeted trap-neuter-return and adoption of community cats on cat intake to a shelter, The Veterinary Journal, Available online 5 May 2014, ISSN 1090-0233, http://dx.doi.org/10.1016/j.tvjl.2014.05.001.