Frank, TNR is an abject failure because it was never meant to be a solution, just a way of avoiding euthanasia.  There is not one single study anywhere on earth that can demonstrate a full feral cat colony attrition as a result of TNR alone.  It has to be used in conjunction with adoption AND euthanasia if you want to have any hope of reducing the feral cat population.  TNR was started 50 years ago in the UK, in that time all it's done is allow their Feral cat population to DOUBLE.  We've been doing TNR in the states for 20 years and we have more feral cats now than ever before.  

"virtually no information exists to support the contention that neutering is an effective long-term method for controlling free-roaming cat populations." "...free-roaming cats do not appear to have sufficient territorial activity to prevent new arrivals from permanently joining colonies."

Levy, Julie K, Evaluation of the Effect of a Long-Term TNR and Adoption program on Free Roaming Cats. JVMA 222(1)4246