I think the odds of fish egg transport via birds is highly dependent on the species of fish. Goldfish eggs are much likely to be transported via birds than sunfish. Goldfish eggs are sticky by nature and stick to vegetation. They are scattered randomly about. Sunfish eggs are not nearly as sticky and are cared for by the parent. This IMO reduces the likelihood that they would be nearly as successful as say goldfish eggs in surviving transport via this method. So, some species are more likely than others to be transported via birds by their eggs but again, I think it is HIGHLY unlikely.
Fish being carried via a bird's mouth is a more plausible solution, particularly over short distances of less than a 1/4 mile or so... Almost everyone has seen a heron drop a fish they recently caught and sometimes after the heron has flown some distance. Some have even seen them drop them into adjacent bodies of water!
I personally think the human factor is the leading cause of fish introduction into new bodies of water. Either through accidental introduction(bait bucket release, fish stock contamination)or through intentional introduction (stocking of fish, neighbor's son put 5 bullhead in your pond without your knowledge).
Bob's point of fish using flood events to reach new bodies of water is spot on IMO. It is truly amazing how far up a TINY stream little green sunfish can go. Some species are better able to utilize flood events better than others. This doesn't usually pertain to colonization of a pond by fish, but the way fish spread from one drainage to another in most cases is referred to as stream capturing.
Stream capture, river capture, or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighboring stream. Often times nothing of major significance as far as fish communities goes happens because this event occurs within the same drainage. However, every so often this occurs between adjacent yet separate drainages. This is when new fish species can colonize and new watershed. This can happen for several reasons, including:
1) Tectonic earth movements, where the slope of the land changes, and the stream is tipped out of its former course.
2) Natural damming, such as by a landslide or ice sheet.
3) Erosion, either
- Headward erosion of one stream valley upwards into another, or
- Lateral erosion of a meander through the higher ground dividing the adjacent streams.
- Within an area of karst topography, where streams may sink, or flow underground (a sinking or losing stream) and then reappear in a nearby stream valley.
Maybe we can have the Discovery Channel show 'Mythbusters' test this out for us?
