At the risk of being repetitive, I'll repeat my first hand observations on the overuse of herbicides...
I am blessed to live in a small farming community with a creek across the street from me. Ca. quail and pheasants reside (or did) in the creek's riparian cover. My elderly neighbors love to scatter waste grain/bird seed on their gravel parking strip to observe these birds. However, that same neighbor is the past manager of the local grain co-op and LOVES chemicals,"They wouldn't sell them to us if it was bad for us". One morning I watched him don his chem-spray backpack and spray his gravel parking area for the evil WEEDS. In literally five minutes after his spraying, his elderly wife is out scattering seed for the covey of 30-40 quail that come up out of the creek. Golly...Guess what(?) the quail and the occasional pheasant disappeared in less than 24 hours and they have yet to reappear. If you think of this on a larger scale; you don't need to wonder on a major contributor to our loss of upland birds. Unfortunately Monsanto, Dow Chemical and others are BIG business and the majority of farmers (inspite of very high incidents of cancer) have my neighbor's mindset. Politicians and state wildlife agencies don't want to take on the actual problem.
From an upland bird hunter on another forum:
"I too have often wondered what effects ag chemicals have upon grassland nesting birds. Years ago when I lived in SC PA I had permission to hunt the farms owned by a large family farming company. I knew one of their workers on a casual basis and asked him one day if he had ever observed ag chemical spaying to have any impact on the local pheasant population. He told me that very Spring he had examined a field that he had personally sprayed with some sort of weed killer, not pesticide, and had found more than a dozen dead pheasants including hens on nests."
Sorry, but I hear the dismissive responses on the effects of the misuse of herbicides and pesticides on a regular basis in my small farming community. I think it as great if not greater risk to our upland birds than the safe "loss of habitat" excuse.