Does TNVR work to reduce cat populations?

Question

On a social website, our neighborhood is having a bit of a debate about local "wild" cat populations. In essence, "wild" cat populations consist of both feral and not-feral but not-homed cats in a colony.

The general consensus (during that argument) is that a "Trap, Neuter, Vaccinate, and Return" (TNVR) policy is an effective (and humane) way to control and eventually remove (through attrition) a wild cat population.

Unfortunately, when looking at different materials, they seems to measure cost reduction, or in some cases "stabilization" or the population, but never at the long term success of a TNVR program.

For example:

TNVR has been shown to be the least costly, most efficient and most humane way to stabilize cat populations. from Tampa bay Humane Society

TNVR stands for Trap – Neuter – Vaccinate – Return. TNVR has been shown to be the most humane, most efficient, and least costly method of stabilizing community cat populations. from MEOW Now

Are there any studies or materials that show that TNVR is actually successful at reducing cat populations, ending in the eventual removal of the population from the neighborhood?

Answer 1

According to the following extract from "The Veterinary Journal" September 2014, The TNR treatment is effective for small-mid size colonies of cats, while larger colonies might prove more difficult to control and reduce.

• Numerous studies have shown that fertility control via TNR is effective in reducing cat colony size over time. A population of 155 cats in 11 colonies on a Florida university campus was reduced to 23 over 11 years, and three colonies became extinct (Levy et al., 2003a). Cats in six colonies in rural North Carolina were reduced by 36% in 2 years and continued to decline or the colonies were extinguished over the next 5 years (Nutter, 2005). In Rome, 103 colonies experienced an average decrease of 22%, while a colony at a Rio de Janeiro zoo fell by 58% over 7 years (Mendes-de-Almeida et al., 2011). In Florida, 132 colonies containing 920 cats were reduced by 26% in the first year of a TNR program (Centonze and Levy, 2002).

• While TNR has been well documented to reduce or eliminate cat populations at the colony level, it has yet to be shown whether the strategy can be adequately scaled up to remain effective over larger areas or can reduce the number of cats impounded in shelters.

• Population models demonstrate that controlling community-wide cat populations via TNR is theoretically possible, but could require sterilization rates of 51–94% (Andersen et al, 2004, Foley et al, 2005, Budke, Slater, 2009, Schmidt et al, 2009 and McCarthy et al, 2013). Cat feeding surveys indicate that there are likely to be at least 100 community cats for every 1000 human residents (Levy et al, 2003b, Lord, 2008 and Kass et al, 2013), suggesting that even relatively small communities can have tens of thousands of cats that might overwhelm the existing local TNR capacity.