They were looking at west nile, but I believe that they did not find that to be the problem. Probably just simply the increases in predators, more raptors, coyotes, fisher, and bobcat. The more predators you have the more they eat. Start in the spring with nest raiders that get eggs, then the poults are hunted hard by those small hawks that raid bird feeders, as well as fox and coyotes getting the small poults. Then if they are lucky enough to get to a size where they roost in the trees the owls start on them, and continue to kill even adult birds, at least hens. As for poults the most I have ever heard of being killed by an owl in one night was three poults about the size of pheasants, two with just the heads removed and a third that was eaten on a little bit. I had a few hens nest at my house, and most young, that hatch, never make it past the sharp shin hawks and cooper hawks to get eaten by anything else. But they are surrounded by electric fence.