<P> The ducks have a cosmopolitan distribution . A number of species manage to live on sub-Antarctic islands like South Georgia and the Auckland Islands . Numerous ducks have managed to establish themselves on oceanic islands such as Hawaii, New Zealand and Kerguelen, although many of these species and populations are threatened or have become extinct . </P> <P> Some duck species, mainly those breeding in the temperate and Arctic Northern Hemisphere, are migratory; those in the tropics, however, are generally not . Some ducks, particularly in Australia where rainfall is patchy and erratic, are nomadic, seeking out the temporary lakes and pools that form after localised heavy rain . </P> <P> Worldwide, ducks have many predators . Ducklings are particularly vulnerable, since their inability to fly makes them easy prey not only for predatory birds but also for large fish like pike, crocodilians, predatory testudines such as the Alligator snapping turtle, and other aquatic hunters, including fish - eating birds such as herons . Ducks' nests are raided by land - based predators, and brooding females may be caught unaware on the nest by mammals, such as foxes, or large birds, such as hawks or owls . </P> <P> Adult ducks are fast fliers, but may be caught on the water by large aquatic predators including big fish such as the North American muskie and the European pike . In flight, ducks are safe from all but a few predators such as humans and the peregrine falcon, which regularly uses its speed and strength to catch ducks . </P>

How many species of ducks are there in north america