How about those chemicals used for no-till farming? Ever since no-till became popular, I've seen fewer rabbits and zero quail in areas that used to have a heckuva lot of both.
You would think that must have an impact. But, as someone pointed out to me, the chemicals used in the '50s and '60s were a lot more toxic than the ones used now, and there were plenty of birds back then. I used to hear that no till was actually going to be better for wildlife. I agree with JamesJr that habitat may be part of it, but there's something else going on.
