Coyotes aren't dummies, nor is Ma Nature as to wasting energy for caloric gains. There is no doubt in my mind that Coyotes are hell on any broody hen and or the eggs of any ground nesting bird species. There should be some truth to the fact that Coyotes eat and keep down other nesting predators but no true research , that I have found, shows that the balance is swayed towards the positive recruitment of a ground nesting species by the coyotes eating other nest predators.
Most certainly Hawks, Owls and Eagles play a huge role in any ground living birds as do snakes where applicable.
It is quite obvious , if one knows the history of game bird be it pheasant, quail, turkey or similar that raptors were kept in check in the days of past. Further I can factually attest that a year round trapping program for coyotes, racoons, skunks, foxes etc will almost always increase recruitment in both game birds and Cervid species.
One of the more and recent worries discovered lies with the widespread and increased use of Neonicotinoids as the go to for insecticides. . Studies have shown that these chemicals greatly affect the reproductive and immune systems, especially in small game birds, in a negative way. The chemicals can be not only transferred by the eating of sprayed grains directly but also from the consumption of dead or dying insects from the chemicals application.
I am not about to step out there and onto the farmers toes but I believe that these chems in particular should be very closely scrutinized.
https://www.ncbi.nlm.nih.gov/pubmed/25177026https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284370/
