Interestingly enough after several hawk induced overflies I bred from the birds that returned, and eventually developed a family of birds that had a relatively good homing instinct. When I first started out an overfly generally meant no birds returning, butI was able to improve their homing ability. One of the problems with rollers (I think) is that due to their relatively small size their energy resources are easily burned up resulting in weakened birds that don't have enugh strength to return home. Our animal control agent frequently brings me 'lost' homers that are little more than feather and bone - these are birds easily 3 times the size of my rollers. It amazes how rapidly these birds rehabilitate. Upon release they generally return to their homes.