The female lays eight to 13 creamy white to greenish-buff spotless eggs, on alternate days. Incubation takes 27 to 28 days and fledging takes 50 to 60 days. The ducklings are precocial and fully capable of swimming as soon as they hatch.
The mallard is considered to be a species of least concern by the International Union for Conservation of Nature (IUCN). Unlike many waterfowl, mallards are considered an invasive species in some regions. It is a very adaptable species, being able to live and even thrive in urban areas which may have supported more localised, sensitive species of waterfowl before development. The non-migratory mallard interbreeds with indigenous wild ducks of closely related species through genetic pollution by producing fertile offspring. Complete hybridisation of various species of wild duck gene pools could result in the extinction of many indigenous waterfowl. The wild mallard is the ancestor of most domestic ducks, and its naturally evolved wild gene pool gets genetically polluted by the domesticated and feral mallard populations.
Taxonomy and evolutionary history
An American black duck (top left) and a male mallard (bottom right) in eclipse plumage
The name Mallard originally referred to any wild drake, and it is sometimes still used this way.[7] It was derived from the Old French malart or mallart for "wild drake" although its true derivation is unclear.[8] 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".[9] Masle (male) has also been proposed as an influence.[10]
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 as the northern pintail, leading to various hybrids that may be fully fertile.[11] This is quite unusual among such different species, and is apparently because the mallard evolved very rapidly and recently, during the Late Pleistocene.[12] The distinct lineages of this radiation are usually kept separate due to non-overlapping ranges and behavioural cues, but have not yet reached the point where they are fully genetically incompatible.[12] Mallards and their domesticated conspecifics are also fully interfertile.[13]
Genetic analysis has shown that certain mallards appear to be closer to their Indo-Pacific relatives while others are related to their American relatives.[14] Mitochondrial DNA data for the D-loop sequence suggests that mallards 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.[15] The large Ice Age palaeosubspecies that made up at least the European and west Asian populations during the Pleistocene has been named Anas platyrhynchos palaeoboschas.[16]
Mallards are differentiated in their mitochondrial DNA between North American and Eurasian populations,[17] but the nuclear genome displays a notable lack of genetic structure.[18] Haplotypes typical of American mallard relatives and spotbills can be found in mallards around the Bering Sea.[19] 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.[15]
Also, the paucity of morphological differences between the Old World mallards and the New World mallard demonstrates the extent to which the genome is shared among them such that birds like the Chinese spot-billed duck are highly similar to the Old World mallard, and birds such as the Hawaiian duck are highly similar to the New World mallard.[20]
The size of the mallard varies clinally; for example, birds from Greenland, though larger, have smaller bills, paler plumage, and stockier bodies than birds further south, and are sometimes classified as a separate subspecies, the Greenland mallard (A. p. conboschas).[21]
Description
Juvenile male and female
Iridescent speculum feathers of the male
A group of mallards quacking
Duckling
The breeding male mallard is unmistakable, with a glossy bottle-green head and a white collar that demarcates the head from the purple-tinged brown breast, grey-brown wings, and a pale grey belly.[25] The rear of the male is black, with white-bordered dark tail feathers.[22]:506 The bill of the male is a yellowish-orange tipped with black, with that of the female generally darker and ranging from black to mottled orange and brown.[26] 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.[22]:506
Both male and female mallards have distinct iridescent purple-blue speculum feathers edged with white, which are prominent in flight or at rest but temporarily shed during the annual summer moult.[27] Upon hatching, the plumage of the duckling is yellow on the underside and face (with streaks by the eyes) and black on the back (with some yellow spots) all the way to the top and back of the head.[28] Its legs and bill are also black.[28] As it nears a month in age, the duckling's plumage starts becoming drab, looking more like the female, though more streaked, and its legs lose their dark grey colouring.[22]:506 Two months after hatching, the fledgling period has ended, and the duckling is now a juvenile.[29] Between three and 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 soon loses its dark grey colouring, and its sex can finally be distinguished visually by three factors: 1) the bill is yellow in males, but black and orange in females;[30][self-published source] 2) the breast feathers are reddish-brown in males, but brown in females;[30] and 3) in males, the centre tail feather (drake feather) is curled, but in females, the centre tail feather is straight.[30] 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 gradually changes to its characteristic colours.[31] This change in plumage 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.[31] The adulthood age for mallards is fourteen months, and the average life expectancy is three years, but they can live to twenty.[32]
Several species of duck have brown-plumaged females that can be confused with the female mallard.[33] The female gadwall (A. strepera) has an orange-lined bill, white belly, black and white speculum that is seen as a white square on the wings in flight, and is a smaller bird.[22]:506 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,[34] and the mottled duck (A. fulvigula), which is somewhat darker than the female mallard, and with slightly different bare-part colouration and no white edge on the speculum.[34]
In captivity, domestic ducks come in wild-type plumages, white, and other colours.[35] 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.[35]
Owing to their highly 'malleable' genetic code, mallards can display a large amount of variation,[36] as seen here with this female, who displays faded or 'apricot' plumage.
The mallard is a rare example of both Allen's Rule and Bergmann's Rule in birds.[38] Bergmann's Rule, which states that polar forms tend to be larger than related ones from warmer climates, has numerous examples in birds,[39] as in case of the Greenland mallard which is larger than the mallards further south.[21] Allen's Rule says that appendages like ears tend to be smaller in polar forms to minimise heat loss, and larger in tropical and desert equivalents to facilitate heat diffusion, and that the polar taxa are stockier overall.[40] Examples of this rule in birds are rare as they lack external ears, but the bill of ducks is supplied with a few blood vessels to prevent heat loss,[41] and, as in the Greenland mallard, the bill is smaller than that of birds farther south, illustrating the rule.[21]
Due to the variability 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).[42]
Distribution and habitat
Male mallard
The mallard inhabits a wide range of habitats and climates, from Arctic tundra to subtropical regions.[57] It is found in both fresh- and salt-water wetlands, including parks, small ponds, rivers, lakes and estuaries, as well as shallow inlets and open sea within sight of the coastline.[58] Water depths of less than 0.9 metres (3.0 ft) are preferred, with birds avoiding areas more than a few metres deep.[59] They are attracted to bodies of water with aquatic vegetation.[22]:507
Behaviour
Feeding
The mallard is omnivorous and very flexible in its choice of food.[60] Its diet may vary based on several factors, including the stage of the breeding cycle, short-term variations in available food, nutrient availability, and interspecific and intraspecific competition.[61] The majority of the mallard's diet seems to be made up of gastropods,[62] invertebrates (including beetles, flies, lepidopterans, dragonflies, and caddisflies),[63] crustaceans,[64] worms,[62] many varieties of seeds and plant matter,[62] and roots and tubers.[64] 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.[65] Plants generally make up the larger part of a bird's diet, especially during autumn migration and in the winter.[66][67]The mallard usually feeds by dabbling for plant food or grazing; there are reports of it eating frogs.[68] However, in 2017 a flock of mallards in Romania were observed hunting small migratory birds, including grey wagtail and black redstart, the first documented occasion they had been seen attacking and consuming large vertebrates.[69] 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.[citation needed]
Breeding
Female Mallard with five ducklings
Egg clutches number 8–13 creamy white to greenish-buff eggs free of speckles.[75][76] They measure about 58 mm (2.3 in) in length and 32 mm (1.3 in) in width.[76] The eggs are laid on alternate days, and incubation begins when the clutch is almost complete.[76] Incubation takes 27–28 days and fledging takes 50–60 days.[75][77] The ducklings are precocial and fully capable of swimming as soon as they hatch.[citation needed] 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.[78] When ducklings mature into flight-capable juveniles, they learn about and remember their traditional migratory routes (unless they are born and raised in captivity).In New Zealand, where Mallards are naturalised, the nesting season has been found to be longer, eggs and clutches are larger and nest survival is generally greater compared with Mallards in their native range. [79]
Drake mallard performing the grunt-whistle[80]
The drakes that end up being left out after the others have paired off with mating partners sometimes target an isolated female duck, even one of a different species, and proceed to chase and peck at her until she weakens, at which point the males take turns copulating with the female.[84] Lebret (1961) calls this behaviour "Attempted Rape Flight", and Stanley Cramp and K.E.L. Simmons (1977) speak of "rape-intent flights".[84] Male mallards also occasionally chase other male ducks of a different species, and even each other, in the same way.[84] 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.[84] This paper was awarded an Ig Nobel Prize in 2003.[85]
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.[86] These eggs are generally accepted when they resemble the eggs of the host mallard, but the hen may attempt to eject them or even abandon the nest if parasitism occurs during egg laying.[87]
Predators and threats
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, felids, and canids, including domesticated ones.[88] The most prolific natural predators of adult mallards are red foxes (which most often pick off brooding females) and the faster or larger birds of prey, e.g. peregrine falcons, Aquila eagles, or Haliaeetus eagles.[89] In North America, adult mallards face no fewer than 15 species of birds of prey, from northern harriers and short-eared owls (both smaller than a mallard) to huge bald and golden eagles, and about a dozen species of mammalian predator, not counting several more avian and mammalian predators who threaten eggs and nestlings.[87]Mallards are also preyed upon by other waterside apex predators, such as the grey heron,[90] European herring gull, the wels catfish, and the northern pike.[91] Crows (Corvus spp.) are also known to kill ducklings and adults on occasion.[92] Also, mallards may be attacked by larger anseriformes such as swans (Cygnus spp.) and geese during the breeding season, and are frequently driven off by these birds over territorial disputes. Mute swans (Cygnus olor) have been known to attack or even kill mallards if they feel that the ducks pose a threat to their offspring.[93]
The predation-avoidance behavior of sleeping with one eye open, allowing one brain hemisphere to remain aware while the other half sleeps, was first demonstrated in mallards, although it is believed to be widespread among birds in general.[94]
Status and conservation
Illustration by Carl Friedrich Deiker (1875)
Several drakes swim in a pond.
Unlike many waterfowl, mallards have benefited from human alterations to the world – so much so that they are now considered an invasive species in some regions.[97] They are a common sight in urban parks, lakes, ponds, and other human-made water features in the regions they inhabit, and are often tolerated or encouraged in human habitat due to their placid nature towards humans and their beautiful and iridescent colours.[27] While most are not domesticated, mallards are so successful at coexisting in human regions that the main conservation risk they pose comes from the loss of genetic diversity among a region's traditional ducks once humans and mallards colonise an area. Mallards are very adaptable, being able to live and even thrive in urban areas which may have supported more localised, sensitive species of waterfowl before development.[98] The release of feral mallards in areas where they are not native sometimes creates problems through interbreeding with indigenous waterfowl.[97][99] These non-migratory mallards interbreed with indigenous wild ducks from local populations of closely related species through genetic pollution by producing fertile offspring.[99] Complete hybridisation of various species of wild duck gene pools could result in the extinction of many indigenous waterfowl.[99] 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.[citation needed]
Over time, a continuum of hybrids ranging between almost typical examples of either species develop; the speciation process is beginning to reverse itself.[100] This has created conservation concerns for relatives of the mallard, such as the Hawaiian duck,[101][102] the New Zealand grey duck (A. s. superciliosa) subspecies of the Pacific black duck,[101][103] the American black duck,[104][105] the mottled duck,[106] Meller's duck,[107] the yellow-billed duck,[100] and the Mexican duck,[101][106] in the latter case even leading to a dispute as to whether these birds should be considered a species[108] (and thus entitled to more conservation research and funding) or included in the mallard species. Ecological changes and hunting have also 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.[103] Hybrid offspring of Hawaiian ducks seem to be less well adapted to native habitat, and using them in re-introduction projects apparently reduces success.[101][109] In summary, the problems of mallards "hybridising 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, hybridisation must have occurred to some extent.[110]
Invasiveness
The last male Mariana mallard
Availability of mallards, mallard ducklings, and fertilised mallard eggs for public sale and private ownership, either as poultry 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.[115]
The mallard is considered an invasive species in New Zealand,[22]:505 where it competes with the local New Zealand grey duck, which was overhunted in the past. There, and elsewhere, mallards are spreading with increasing urbanisation and hybridising with local relatives.[101]
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.[19] The Mariana mallard was a resident allopatric population – in most respects a good species – apparently initially derived from mallard-Pacific black duck hybrids;[116] unfortunately, it became extinct in the late 20th century.[117]
The Laysan duck is an insular relative of the mallard, with a very small and fluctuating population.[118][1] Mallards sometimes arrive on its island home during migration, and can be expected to occasionally have remained and hybridised with Laysan ducks as long as these species have existed.[119] However, these hybrids are less well adapted to the peculiar ecological conditions of Laysan Island than the local ducks, and thus have lower fitness. Laysan ducks were found throughout the Hawaiian archipelago before 400 CE, after which they suffered a rapid decline during the Polynesian colonisation.[120] Now, their range includes only Laysan Island.[120] It is one of the successfully translocated birds, after having become nearly extinct in the early 20th century.[121]
Domestication
Mallards have often been ubiquitous in their regions among the ponds, rivers, and streams of human parks, farms, and other human-made waterways – even to the point of visiting water features in human courtyards.[122]
Mallards have had a long relationship with humans. Almost all domestic duck breeds derive from the mallard, with the exception of a few Muscovy breeds.[123] Mallards are generally monogamous while domestic ducks are mostly polygamous. Domestic ducks have no territorial behaviour and are less aggressive than mallards.[124] Domestic ducks are mostly kept for meat; their eggs are also eaten, and have a strong flavor.[124] They were first domesticated in Southeast Asia at least 4,000 years ago, during the Neolithic Age, and were also farmed by the Romans in Europe, and the Malays in Asia.[125] As the domestic duck and the mallard are the same species as each other, It is common for mallards to mate with domestic ducks and produce hybrid offspring that are fully fertile.[126] Because of this, mallards have been found to be contaminated with the genes of the domestic duck.[126]
While the keeping of domestic breeds is more popular, pure-bred mallards are sometimes kept for eggs and meat,[127] although they may require wing clipping to restrict flying, or training to navigate and fly home.[128]
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As food
Since ancient times, the mallard has been eaten as food. The wild mallard was eaten in Neolithic Greece.[132] Usually, only the breast and thigh meat is eaten.[133] It does not need to be hung before preparation, and is often braised or roasted, sometimes flavoured with bitter orange or with port.[134]Anas platyrhynchos
Linnaeus, 1758
Range of A. platyrhynchos
Breeding Resident Passage Non-breeding Vagrant (seasonality uncertain) Possible extinct & Introduced Extant & Introduced (seasonality uncertain) Possibly Extant & Introduced (seasonality uncertain)
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