*Egg is laid (and may or may not have been fertilized)
*Egg is dislodged by a wading bird (likely mechanical damage)
*Egg travels out of water for a distance (exposure to air weakens defenses/shock from temp changes)
*Egg is shaken off the bird foot (more likely mechanical damage)
*Egg falls to the pond bottom (probable predation by insects, crustaceans, bacteria, fungus, etc)
*Egg hatches (still open to predation, must have an opposite sex/same species fish introduced in the same way, and they must live to maturity to reproduce)
The odds seem staggering to me.
I'm with you on that one GW. I've never observed fish eggs on a bird's feet... though given enough years and a million ponds, it will certainly happen.
I
have observed birds being forced by harassing birds to drop their catch. I have also observed a bird with live gambusia fry stuck to its beak. They obvously came from a pregnant gambusia that was just eaten by the bird. They could probably survive on the bird's beak for 10-15 minutes in humid conditions.
If you have a sterile pond within 1 mile of other waters, I think there's a probability curve for the pond being incidentally "innoculated".
I'm guessing that in a given year, there's up to 1 chance in 4 of getting gambusia, 1 in 10 chance per year of getting a cat fish, and 1 in 20 of getting a sunfish. My WAG is for illustration only, and I may be off a lot either way. But you can see that in 10 years you will most likely get a handful of fish.
The debate is not that important anyway. It's more about principle than a practical matter. Getting an occasional fish dropped into your pond is harmless most of the time, because the interloper is probably eaten right away in a strange environment.
