Crazy , along the Delaware is precisely one of the areas I've been to field trials and watched hawk after hawk come down and take birds.
If everyone would READ my post you will see I believe it's a combination of things not just one particular problem. I do believe however desease is well down on the list. Deseases that hit domestic poultry are sporadic at best over the years and dealt with quickly and in no half measure way when they do appear. IMHO that would have an overall minimum cause and effect on what made the population crash.