This is reflected in the species composition of ducks at M vatn and Lax and nowhere else in the world can the same mixture of species be found. The Barrow's Goldeneye and the Harlequin Duck have their origin in America. The Long-tailed Duck, Scaup and the Common Scoter are examples of arctic and subarctic species. The diverse habitat contributes to the diversity of ducks. All the species have conditions which meet their special requirements.
Nesting habitats are varied.
Holes for hole-nesting ducks like the Barrow's Goldeneye are abundant. The bottom of the lake also varies from place to place. Even though some areas lack food in one year there are always areas where food is abundant. Finally it seems possible that moderate fluctuations in the environment may play a role in keeping the diversity high. These fluctuations apparently keep the duck populations in a constant state of succession and may prevent some few species from taking over.