Mallard - Conservation

Conservation

Unlike many waterfowl, Mallards have benefited from human alterations to the world. They are very adaptable, being able to live and even thrive in urban areas which may have supported more localized, sensitive species of waterfowl before development. The release of feral Mallards in areas where they are not native sometimes creates problems through interbreeding with indigenous waterfowl. These non-migratory Mallards interbreed with indigenous wild ducks from local populations of closely related species through genetic pollution by producing fertile offspring. Complete hybridization of various species of wild ducks gene pools could result in the extinction of many indigenous waterfowl. The wild Mallard itself is the ancestor of most domestic ducks and its naturally evolved wild gene pool gets genetically polluted in turn by the domesticated and feral populations.

The Mallard is considered an invasive species in New Zealand. There, and elsewhere, Mallards are spreading with increasing urbanization and hybridizing with local relatives. Over time, a continuum of hybrids ranging between almost typical examples of either species will develop; the speciation process beginning to reverse itself. This has created conservation concerns for relatives of the Mallard, such as the Hawaiian Duck, the A. s. superciliosa subspecies of the Pacific Black Duck, the American Black Duck, the Mottled Duck, Meller's Duck, the Yellow-billed Duck, and the Mexican Duck, in the latter case even leading to a dispute whether these birds should be considered a species (and thus entitled to more conservation research and funding) or included in the Mallard.

The availability of Mallards, Mallard ducklings, and fertilized Mallard eggs for public sale and private ownership, either as livestock or as pets, is currently legal in the United States except for the state of Florida which has currently banned domestic ownership of Mallards. This is to prevent hybridisation with the native Mottled Duck.

Mallards are also causing severe "genetic pollution" of South Africa's biodiversity by breeding with endemic ducks, although the Agreement on the Conservation of African-Eurasian Migratory Waterbirds applies to the Mallard. The hybrids of Mallards and the Yellow-billed Duck are fertile and can produce more hybrid offspring. If this continues, only hybrids will occur and in the long term this will result in the extinction of various indigenous waterfowl. The Mallard duck can cross breed with 63 other species and is posing a severe threat to the genetic integrity of indigenous waterfowl. Mallards and their hybrids compete with indigenous birds for resources such as food, nest sites and roosting sites.

The Eastern or Chinese Spot-billed Duck is currently introgressing into the Mallard populations of the Primorsky Krai, possibly due to habitat changes from global warming. The Mariana Mallard was a resident allopatric population—in most respects a good species—apparently initially derived from Mallard-Pacific Black Duck hybrids; unfortunately, it became extinct in the 1980s. In addition, feral domestic ducks interbreeding with Mallards have led to a size increase—especially in drakes—in most Mallards in urban areas. Rape flights between normal-sized females and such stronger males are liable to end with the female being drowned by the males' combined weight.

The Laysan Duck is an insular relative of the Mallard with a very small and fluctuating population. Mallards sometimes arrive on its island home during migration, and can be expected to occasionally have remained and hybridized with Laysan Ducks as long as these species have existed. But these hybrids are less well adapted to the peculiar ecological conditions of Laysan Island than the local ducks, and thus have lower fitness, and furthermore, there were—apart from a brief time in the early 20th century when the Laysan Duck was almost extinct—always many more Laysan Ducks than stray Mallards. Thus, in this case, the hybrid lineages would rapidly fail.

In the cases mentioned above, however, ecological changes and hunting have led to a decline of local species; for example, the New Zealand Grey Duck population declined drastically due to overhunting in the mid-20th century. Hybrid offspring of Hawaiian Ducks seem to be less well-adapted to native habitat, and utilizing them in reintroduction projects apparently reduces success. In summary, the problems of Mallards "hybridizing away" relatives is more a consequence of local ducks declining than of Mallards spreading; allopatric speciation and isolating behaviour have produced today's diversity of Mallard-like ducks despite the fact that in most if not all of these populations, hybridization must have occurred to some extent.