Here is my perspective. I am managing my property for upland birds, pheasant but more specifically hopefully someday...quail(again). I am not a bird hunter per say but I do like to deer hunt. If I manage for birds deer are a welcome by product. Some of the things I have done. I have killed out all my cool season grasses and promote forbs. I am introducing fire to my landscape. There is a direct correlation between cattle and quail so I now have them to create the disturbance on the ground.
There are two main reasons loss of habitat but also spraying. You can argue all you want about if glysophate (round up) is good or bad. But when you kill one thing several others are affected. One of the main forages for poults are insects...if you spray to kill pests then you are going to kill the critters that feed on them. Same with weeds.
I also believe neonix seed treatment is killing alot of birds in agricultural areas.