What about wildlife predation?
We at PACT Humane Society, along with other other TNR practitioners, are also concerned about nature's other animals.
Even the experts disagree on the topic of feral cats & wildlife predation. Some blame declining bird populations to feral cats while others point to pesticide use and depletion of natural habitat -- problems caused by humans. The West Nile Virus wiped out nearly 90% of the blue jay population in Illinois years ago. The Internet is packed full of statistics, studies and opinions.
The bottom line for us is: since TNR (humanely) reduces the number of feral cats, there will be less predation.
(Interestingly, feral and domesticated cats hunt mice and rats, but there isn't a shortage of them.)