>Maybe the impact is simply that outside house cats exist in numbers that are not supportable for a normal wild predator due to the fact that house cats have meals provided by humans to sustain them. So house cat numbers don't reach an equilibrium with their prey the way a wild cat could.

That's exactly it. The density of house cats is orders of magnitude larger than the density of wildcats would be.

> Either way I suspect that the impact on bird populations by domestic cats is often overstated.

Why?