You have better odds catching a 10+ pound bass in the north than eggs sticking to a bird's legs and surviving to hatch in another pond. Herons or raptors dropping fish, almost as rare unless ponds are adjacent to each other. I know of several ponds that after years, 10+ still have no fish in them. Fish finding a new home in a pond is by humans, either on intentionally(with or without permission) or unintentionally(stock contamination, improper identification). Natural movement during high water events. They either get flooded down stream from a pond above yours or ascend your outflow into your pond.
