Mallard / Wild Duck (Anas platyrhynchos)
The mallard (/ˈmælɑrd/ or /ˈmælərd/) or wild duck (Anas platyrhynchos) is a dabbling duck which breeds throughout the temperate and subtropical Americas, Europe, Asia, and North Africa, and has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Argentina, Chile, the Falkland Islands and South Africa. This duck belongs to the subfamily Anatinae of the waterfowl family Anatidae.
The male birds (drakes) have a glossy green head and are grey on wings and belly, while the females have mainly brown-speckled plumage. Mallards live in wetlands, eat water plants and small animals, and are gregarious. This species is the ancestor of most breeds of domestic ducks.
Taxonomy and evolution
The name mallard is derived from the Old French malart or mallart “wild drake”, although its ultimate derivation is unclear. It may be related to (or at least influenced by) an Old High German masculine proper name Madelhart, clues lying in the alternate English forms “maudelard” or “mawdelard”. Masle (male) has also been proposed as an influence.
Mallards frequently interbreed with their closest relatives in the genus Anas, such as the American black duck, and also with species more distantly related, such the northern pintail, leading to various hybrids that may be fully fertile. This is quite unusual among such different species, and apparently is because the mallard evolved very rapidly and recently, during the Late Pleistocene. The distinct lineages of this radiation are usually kept separate due to non-overlapping ranges and behavioural cues, but are still not fully genetically incompatible. Mallards and their domesticated conspecifics are also fully interfertile.
The genome of Anas platyrhynchos was sequenced in 2013.
Mallards appear to be closer to their Indo-Pacific relatives than to their American ones judging from biogeography. Considering mitochondrial DNA D-loop sequence data, they may have evolved in the general area of Siberia; mallard bones rather abruptly appear in food remains of ancient humans and other deposits of fossil bones in Europe, without a good candidate for a local predecessor species. The large ice age palaeosubspecies which made up at least the European and west Asian populations during the Pleistocene has been named Anas platyrhynchos palaeoboschas.
In their mitochondrial DNA, mallards are differentiated between North America and Eurasia, however, in the nuclear genome there is a particular lack of genetic structure. Haplotypes typical of American mallard relatives and spotbills can be found in mallards around the Bering Sea. The Aleutian Islands hold a population of mallards that appear to be evolving towards a subspecies, as gene flow with other populations is very limited.
The size of the mallard varies clinally, and birds from Greenland, although larger than birds further south, have smaller bills and are stockier. They are sometimes separated as subspecies, the Greenland mallard (A. p. conboschas).
The mallard is a medium-sized waterfowl species although is often slightly heavier than most other dabbling ducks.
The breeding male mallard is unmistakable, with a glossy bottle-green head and white collar which demarcates the head from the purple-tinged brown breast, grey brown wings, and a pale grey belly. The rear of the male is black, with the dark tail having white borders. The bill of the male is a yellowish orange tipped with black while that of the female is generally darker ranging from black to mottled orange. The female mallard is predominantly mottled with each individual feather showing sharp contrast from buff to very dark brown, a coloration shared by most female dabbling ducks, and has buff cheeks, eyebrow, throat and neck with a darker crown and eye-stripe.
Both male and female mallards have distinct iridescent purple blue speculum feathers edged with white, prominent in flight or at rest, though temporarily shed during the annual summer moult. Upon hatching, the plumage colouring of the duckling is yellow on the underside and face (with streaks by the eyes) and black on the backside (with some yellow spots) all the way to the top and back of the head. Its legs and bill are also black. As it nears a month in age, the duckling’s plumage will start becoming drab, looking more like the female (though its plumage is more streaked) and its legs will lose their dark grey colouring. Two months after hatching, the fledgling period has ended and the duckling is now a juvenile. Between three to four months of age, the juvenile can finally begin flying as its wings are fully developed for flight (which can be confirmed by the sight of purple speculum feathers). Its bill will soon lose its dark grey colouring and its sex can finally be distinguished by three factors. The bill colouring is yellow in males, black and orange for females. The breast feathers are reddish-brown for males, brown for females. The centre tail feather is curled for males (called a drake feather), straight for females.
During the final period of maturity leading up to adulthood (6–10 months of age), the plumage of female juveniles remains the same while the plumage of male juveniles slowly changes to its characteristic colours. This plumage change also applies to adult mallard males when they transition in and out of their non-breeding eclipse plumage at the beginning and the end of the summer moulting period. The adulthood age for mallards is 14 months and the average life expectancy is 3 years, but they can live to twenty.
Several species of duck have brown-plumaged females which can be confused with the female mallard. The female gadwall (A. strepera) has an orange-lined bill, white belly, black and white speculum which is seen as a white square on the wings in flight, and is a smaller bird. More similar to the female mallard in North America are the American black duck (A. rubripes), which is notably darker hued in both sexes than the mallard, and the mottled duck (A. fulvigula), which is somewhat darker than the female mallard, with no white edge on the speculum and slightly different bare-part colouration.
In captivity, domestic ducks come in wild-type plumages, white, and other colours. Most of these colour variants are also known in domestic mallards not bred as livestock, but kept as pets, aviary birds, etc., where they are rare but increasing in availability.
The mallard is a rare example of both Allen’s Rule and Bergmann’s Rule in birds. Bergmann’s Rule, which states that polar forms tend to be larger than related ones from warmer climates, has numerous examples in birds. Allen’s Rule says that appendages like ears tend to be smaller in polar forms to minimize heat loss, and larger in tropical and desert equivalents to facilitate heat diffusion, and that the polar taxa are stockier overall. Examples of this rule in birds are rare, as they lack external ears. However, the bill of ducks is very well supplied with blood vessels and is vulnerable to cold.
Due to the malleability of the mallard’s genetic code, which gives it its vast interbreeding capability, mutations in the genes that decide plumage colour are very common and have resulted in a wide variety of hybrids such as Brewer’s duck (mallard × gadwall, Anas strepera).
The mallard is omnivorous and very flexible in its foods choice. Its diet may vary based on several factors, including the stage of the breeding cycle, short-term variations in available food, nutrient availability, and inter and intraspecific competition. The majority of the mallard’s diet seems to be made up of gastropods, invertebrates (including beetles, flies, lepidopterans, dragonflies, and caddisflies), crustaceans, worms, many varieties of seeds and plant matter, and roots and tubers. During the breeding season, male birds were recorded to have eaten 37.6% animal matter and 62.4% plant matter, most notably Echinochloa crus-galli, and nonlaying females ate 37.0% animal matter and 63.0% plant matter, while laying females ate 71.9% animal matter and only 28.1% plant matter. Plants generally make up a larger part of the bird’s diet, especially during autumn migration and in the winter.
It usually feeds by dabbling for plant food or grazing; there are reports of it eating frogs. It usually nests on a river bank, but not always near water. It is highly gregarious outside of the breeding season and forms large flocks, which are known as sords.
Mallards usually form pairs (in October and November in the Northern hemisphere) only until the female lays eggs at the start of nesting season which is around the beginning of spring, at which time she is left by the male who joins up with other males to await the moulting period which begins in June (in the Northern hemisphere). During the brief time before this, however, the males are still sexually potent and some of them either remain on standby to sire replacement clutches (for female Mallards that have lost or abandoned their previous clutch) or forcibly mate with females that appear to be isolated or unattached regardless of their species and whether or not they have a brood of ducklings.
The nesting period can be very stressful for the female since she lays more than half her body weight in eggs. She requires a lot of rest and a feeding/loafing area that is safe from predators. When seeking out a suitable nesting site, the female’s preferences are areas that are well concealed, inaccessible to ground predators, or have few predators nearby. This can include nesting sites in urban areas such as roof gardens, enclosed courtyards, and flower boxes on window ledges and balconies more than one story up, which the ducklings cannot leave safely without human intervention. The clutch is 8–13 eggs, which are incubated for 27–28 days to hatching with 50–60 days to fledgling. The ducklings are precocial and fully capable of swimming as soon as they hatch. However, filial imprinting compels them to instinctively stay near the mother not only for warmth and protection but also to learn about and remember their habitat as well as how and where to forage for food. When ducklings mature into flight-capable juveniles, they learn about and remember their traditional migratory routes (unless they are born and raised in captivity). After this, the juveniles and the mother may either part or remain together until the breeding season arrives.
When they pair off with mating partners, often one or several drakes end up left out. This group sometimes targets an isolated female duck, even one of a different species, and proceeds to chase and peck at her until she weakens, at which point the males take turns copulating with the female. Lebret (1961) calls this behaviour “Attempted Rape Flight” and Cramp & Simmons (1977) speak of “rape-intent flights”. Male mallards also occasionally chase other male ducks of a different species, and even each other, in the same way. In one documented case of “homosexual necrophilia”, a male mallard copulated with another male he was chasing after the chased male died upon flying into a glass window. This paper was awarded with an Ig Nobel Prize in 2003.
Mallards are opportunistically targeted by brood parasites, occasionally having eggs laid in their nests by Redheads, ruddy ducks, lesser scaup, gadwalls, northern shovelers, northern pintails, cinnamon teal, common goldeneyes, and other mallards. These eggs are generally accepted when they resemble the eggs of the host mallard, although the hen may attempt to eject them or even abandon the nest if parasitism occurs during egg laying. Mallards of all ages (but especially young ones) and in all locations must contend with a wide diversity of predators including raptors, mustelids, corvids, snakes, raccoons, opossums, skunks, turtles, large fish and felids and canids, including domesticated ones. The most prolific natural predators of adult mallards are red fox and hawks, although both kill far fewer than human hunters.
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.