Something other than hunting/habitat is responsible for wild Bird numbers declining.
Like so many things I think it's a complex combination of factors. After being born in Pittsburg my Dad was transferred to Chicago so I grew up in the south suburbs.
Back then it was a mix of small corn/bean fields, homes that sprung out of fields and of course the Cook County forest preserve which was almost all sapling forests or wild grass. We had pheasants everywhere to the point my friends and I would crawl along the edge of the fields and shoot them in the heads with air rifles. These were later cooked over an open fire near our treehouse. There was no actual hunting allowed in Cook County so this got us in some trouble then that was dealt with quietly by police and parents and now would like get us put in jail.
Anyway this was the early 70's and was typical of all over the midwest. Stop and look at a plowed field and you'd give up counting pheasants. My Dad and I would take an annual trip to Iowa and Nebraska and same thing for quail out there. Then it all started to crash. Really bad consecutive winters in 77/78, edge to edge farming practices increased airborne and surface predators all take their toll. In 1980 my Dad was transferred to central IN and I think we got the last of some decent grouse in Brown, Morgan and Monroe counties. By that point, even in the glaciated counties north of the hills there were very few pheasants. That had largely disappeared in less than 10 years.
I was up in NH a couple weeks ago and had a guide for a trout trip. He was saying grouse hunting in NH is in decline but VT and ME remain strong due to small woodlot cutting and regrowth in those states and less so in NH. I hope to prove him wrong soon
On the topic of live vs clay. In my experience you won't find many good clays shooters that approach the category of "poor" for actual hunting but the opposite isn't true.
