While a search on the internet will lead you to differing opinions on feral cats and wildlife predation, the majority of scientific evidence points to environmental degradation such as pesticide use and depletion of natural habitats as the main culprit behind declining bird populations. The West Nile Virus wiped out nearly 90% of the blue jay population in Illinois in 2005. In any case, since TNR humanely reduces the number of feral cats, there will be less predation. Although, it is interesting to note that feral and domesticated cats hunt mice and rats, but there still isn’t a shortage of them!
10.19.2011: Feral Cats & Wildlife Predation