Most farms now use no till planting and no till is the bane of wildlife habitat, The use of herbicided in no till farming doesn't allow weeds to gro between the corn rows or in soybean fields and those weeds are food for wildlife. In addition, combining corn and then mowing and baling the stubble for bedding is another death knell to wildlife habitat and food, especially pheasants and rabbits here in the east. When I first started hunting aT 12 YO the weeds between the corn rows were as high as I was because cultivating between the rows when the corn was small did not do a good job of keeping weeds down. I used to have to remove my shirt and undershirt at lunch time to get all the seeds out that went down my shirt front. Then, with the corn picker, the stalks were stripped of ears and bent to the ground leaving exceptional cover and lots of food because pickers missed a lot. Now after the combine goes through a corn field and the stubble is cut and baled the field is a biological desert, then of course there is the manure slurry that is spread on the fields immediately after. Then as TG stated, fence rows and treelines between fields and old orchards were all torn out to get a few more feet to plant corn or soy beans. I suspect if you really pay attention, you will see that the farming practices in your area have changed substantially. To have a good populatrion of pheasants you need contiguious cover along with good edge cover and food to hold them through the winter.