Bill,
I haven't put allot of thought into this, but I know from personal experience that some things pass right through me at times, and they look just like they did going in.
Maybe birds don't have this happen to them, but I've seen lots of undigested seeds and stuff I couldn't identify in bird poop.
I think it's more likely that a bird ate some fish eggs that didn't agree with it and they passed right through there systems in perfect condition. Either that, or they at so many that they could only digest a certain amount of them. Even 99 percent leaves enough to survive in a new pond.
Eddie
