I can say that in the several years that I have been birding the heck out of the northern half of Anne Arundel County that I have seen Bobwhite almost totally disappear.  

The birds did hold on here for a long time in the face of catastrophic habitat loss in the last 5-10 years.  In 2004, two continued to call from a hedge row next to the first hole at the new Compass Pointe Golf Course.  I've had none there since them. Even the populations that were in areas that are still undisturbed are gone.  My only Bobwhite for the year in northern AA county was one random bird calling at Swan Creek in the late spring.  Also had them calling at Greenbury Point, in southern AA county. 

What happened here in north Arundel has 100 percent to do with habitat loss and probably 0 percent to do with hunting. Almost all of the open land that used to host them is gone and what is left is fragmented or for some reason unattractive to them.

Matt Grey
Pasadena