Yes goldfish are eaten by avian predators. They are also prone to attack by domestic cats. There is no gloomier sight for the enthusiastic ornamental fish owner than the golden tail of a prize shubunkin disappearing down the family cat's throat. The main avian predator on garden pond goldfish are herons. Herons have a brilliant talent fro spotting garden ponds as they fly over and once they have discovered one they will keep on fishing there day after day until all your goldfish are eaten. They are early risers and free to gobble up your goldfish whie you are still in bed. Kingfishers have been known to predate on domestic goldfish in garden ponds but only in areas near rivers as they do not travel far to hunt. Heron netting which covers the whole surface of the pond can be ugly, will become clogged with autumn leaves and will affect pond maintenance but it does work. There is no evidence that plastic herons posed on the banks will dissuade the real thing from landing. A line of fine cotton linked to a ring of canes planted around the water's edge is considered effective as the herons don't like the threat of becoming entangled.