Bill,
I didn't believe that either until I toured a very large goldfish farm in southern Indiana and the operator who very knowledgable believes it indeed does happen albeit for short distances at a time. He has some specialty goldfish that are very unique and have shown up in recreations ponds in the area miles away. The goldfish production facility is frequented by wading birds but is secure from trespassers. He indicated he has no doubt that eggs may have been transported by lodging between the webbing of birds like herons as they fly (webbing folds together in the bird's flying position), and then deposited in a neighboring pond. He thinks over time these eggs are moved by "pond hiking" from pond to pond.
I see no reason to doubt this as a possibility as, as long as there is moisture in the webbing of fish eating birds eggs could survive for short periods of time.
Trout and Salmon eggs can be shipped "green" for 24 hours as long as they are moist but make no contact with water. Eyed eggs of trout and salmon are shipping on ice all the time.
