I think you are more likely to find a coevolutionary answer, as opposed to a cause effect.
quote: Do you think it is possible that there is an existing species of bird that has an innate instinct to populate a new pond by transporting fish from an existing pond?
answer: No
Possible rephrasing: Do you think that species, in this case birds and fish, coevolve in a way that benefits both species?
Sometimes yes, and in this case, maybe.
Think of it this way. There could possibly be a manner of feeding and transportation favored by a particular bird, that allowed a transportation mode for fish, which in turn populated ponds, which in turn benefited the bird in question. This could have led to better fitness/survival of that particular bird and it's sloppy fish handling habits.
Purely opinion, of course.
