bz interesting observation about BG being reluctant night feeders. If I recall you have LMB in your pond also. LMB are awesome night feeders and have the sensory advantage over BG at night. This may explain why most BG don't venture far at night. To easy for them to get picked off as a LMB snack. I wonder if locating the bug zapper over or close to some thick cover , like a triangle of xmas trees or weed bed would increase the BG night feeding ?