Mallard Ducks as Agents of Species Extinction

John Hawks has an article on his blog summarising research that suggests that the spread of mallard ducks around the world is causing the extinction of many closely-related species of duck. Mallards introduced by man are hybridising with the local ducks leading to noticable drops in the numbers of pure-bred local ducks. This is happening with the black duck in North America and Australia, the grey duck in New Zealand, the Hawaiian duck, and the Florida mottled duck.  Notice that this is not a question of the mallards killing off the local ducks, it is just that they are making the local ducks offspring more 'mallardish'.  It is a matter of loss of diversity rather than one of genocide.