Mallard_Anas platyrhynchos
Ecology
The Mallard inhabits most wetlands, including parks, small ponds and rivers, and usually feeds by dabbling for plant food or grazing; there are reports of it eating frogs.[2] It usually nests on a river bank, but not always near water. It is highly gregarious outside of the breeding season and will form large flocks, which are known as a sord.[6]
[edit] Breeding behavior
Mallards form pairs only until the female lays eggs, at which time she is left by the male. 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 can swim and feed themselves on insects as soon as they hatch, although they stay near the female for protection.
When they pair off with mating partners, often one or several drakes will end up "left out". This group will sometimes target an isolated female duck — chasing, pestering and pecking at her until she weakens (a phenomenon referred to by researchers as rape flight), at which point each male will take turns copulating with the female. Male Mallards will also occasionally chase other males in the same way. (In one documented case, a male Mallard copulated with another male he was chasing after said male had been killed when he flew into a glass window.)[7]
[edit] Ancestor of domestic ducks
Mallard (Anas platyrhynchos) is the ancestor of almost all of the varieties of domestic ducks. Domestic ducks belong to the subfamily Anatinae of the waterfowl family Anatidae. The wild Mallard and Muscovy duck (Cairina moschata) are believed to be the ancestors of all domestic ducks.[3][4]
[edit] Genetic pollution, hybridization and systematics
The last male Mariana Mallard.
The release of feral Mallard Ducks 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.[3][4][8][9][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, for example the Northern Pintail, leading to various hybrids that may be fully fertile. This is quite unusual among different species, and apparently has its reasons in the fact that the Mallard evolved very rapidly and not too long ago, during the Late Pleistocene only. The distinct lineages of this radiation are usually kept separate due to non-overlapping ranges and behavioral cues, but are still not fully genetically incompatible. Mallards and their domesticated conspecifics are, of course, also fully interfertile.
The Mallard is considered an invasive species in New Zealand. There, and elsewhere, Mallards are spreading with increasing urbanization and hybridizing with local relatives.[11] Over time, a continuum of hybrids ranging between almost typical examples of either species will develop; the speciation process beginning to reverse itself.[12] This has created conservation concerns for relatives of the Mallard, such as the Hawaiian Duck,[13] the A. s. superciliosa subspecies of the Pacific Black Duck,[14] the American Black Duck,[15] the Florida Duck,[16] Meller's Duck,[17] the Yellow-billed Duck,[12] and the Mexican Duck,[18] in the latter case even leading to a dispute whether these birds should be considered a species[19] (and thus entitled to more conservation research and funding) or included in the mallard.
Like elsewhere worldwide the alien Mallards are also causing severe “genetic pollution” of South Africa’s biodiversity by breeding with endemic ducks. The hybrids of Mallard 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.[10]
On the other hand, the Chinese Spotbill is currently introgressing into the Mallard populations of the Primorsky Krai, possibly due to habitat changes from global warming.[20] The Mariana Mallard was a resident allopatric population - in most respects a good species - apparently initially derived from Mallard × Pacific Black Duck hybrids;[21] 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.
It was generally assumed that as the spectacular nuptial plumage of Mallard drakes is obviously the result of sexual selection - most species in the mallard group being sexually monomorphic -, hybrid matings would preferentially take place between females of monomorphic relatives and Mallard drakes instead of the other way around. But this generalization was found to be incorrect.[22]
Note that it is not the hybridization itself that causes most conservation concerns. 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 exist. 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 much 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 Gray Duck's population declined drastically due to overhunting in the mid-20th century (Williams & Basse 2006). In the Hawaiian Duck, it seems that hybrid offspring are less well-adapted to native habitat and that utilizing them in reintroduction projects makes these less than successful.[23] In conclusion, the crucial point underlying the problems of Mallards "hybridizing away" relatives is far less a consequence of Mallards spreading, but of local ducks declining; allopatric speciation and isolating behavior have produced today's diversity of Mallard-like ducks despite the fact that in most if not all of these populations, hybridization must always have occurred to some extent. Given time and a population of sufficient size exists, natural selection ought to suppress harmful allele combinations to a negligible level.
The aforementioned confounds analysis of the evolution considerably. Analyses of good samples of mtDNA sequences give the confusing picture[24] one expects from a wide-ranging species that has evolved probably not much earlier than the Plio-/Pleistocene boundary, around 2 mya. Mallards appear to be closer to their Indo-Pacific relatives than to their American ones judging from biogeography. Considering mtDNA D-loop sequence data,[25] they may have evolved more probably than not 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 paleosubspecies which made up at least the European and W Asian populations during the Pleistocene has been named Anas platyrhynchos palaeoboschas.
As expected, haplotypes typical of American Mallard relatives and Spotbills can be found in Mallards around the Bering Sea.[26] Interestingly, the Aleutian Islands turned out to hold a population of Mallards that appear to be evolving towards a good subspecies as gene flow with other populations is very limited.[25] This unexpected result suggests that reevaluation of the Greenland, Iceland, and NE Canada populations according to molecular and morphological characters is warranted.
Mallard_Anas platyrhynchos
Ecology
The Mallard inhabits most wetlands, including parks, small ponds and rivers, and usually feeds by dabbling for plant food or grazing; there are reports of it eating frogs.[2] It usually nests on a river bank, but not always near water. It is highly gregarious outside of the breeding season and will form large flocks, which are known as a sord.[6]
[edit] Breeding behavior
Mallards form pairs only until the female lays eggs, at which time she is left by the male. 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 can swim and feed themselves on insects as soon as they hatch, although they stay near the female for protection.
When they pair off with mating partners, often one or several drakes will end up "left out". This group will sometimes target an isolated female duck — chasing, pestering and pecking at her until she weakens (a phenomenon referred to by researchers as rape flight), at which point each male will take turns copulating with the female. Male Mallards will also occasionally chase other males in the same way. (In one documented case, a male Mallard copulated with another male he was chasing after said male had been killed when he flew into a glass window.)[7]
[edit] Ancestor of domestic ducks
Mallard (Anas platyrhynchos) is the ancestor of almost all of the varieties of domestic ducks. Domestic ducks belong to the subfamily Anatinae of the waterfowl family Anatidae. The wild Mallard and Muscovy duck (Cairina moschata) are believed to be the ancestors of all domestic ducks.[3][4]
[edit] Genetic pollution, hybridization and systematics
The last male Mariana Mallard.
The release of feral Mallard Ducks 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.[3][4][8][9][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, for example the Northern Pintail, leading to various hybrids that may be fully fertile. This is quite unusual among different species, and apparently has its reasons in the fact that the Mallard evolved very rapidly and not too long ago, during the Late Pleistocene only. The distinct lineages of this radiation are usually kept separate due to non-overlapping ranges and behavioral cues, but are still not fully genetically incompatible. Mallards and their domesticated conspecifics are, of course, also fully interfertile.
The Mallard is considered an invasive species in New Zealand. There, and elsewhere, Mallards are spreading with increasing urbanization and hybridizing with local relatives.[11] Over time, a continuum of hybrids ranging between almost typical examples of either species will develop; the speciation process beginning to reverse itself.[12] This has created conservation concerns for relatives of the Mallard, such as the Hawaiian Duck,[13] the A. s. superciliosa subspecies of the Pacific Black Duck,[14] the American Black Duck,[15] the Florida Duck,[16] Meller's Duck,[17] the Yellow-billed Duck,[12] and the Mexican Duck,[18] in the latter case even leading to a dispute whether these birds should be considered a species[19] (and thus entitled to more conservation research and funding) or included in the mallard.
Like elsewhere worldwide the alien Mallards are also causing severe “genetic pollution” of South Africa’s biodiversity by breeding with endemic ducks. The hybrids of Mallard 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.[10]
On the other hand, the Chinese Spotbill is currently introgressing into the Mallard populations of the Primorsky Krai, possibly due to habitat changes from global warming.[20] The Mariana Mallard was a resident allopatric population - in most respects a good species - apparently initially derived from Mallard × Pacific Black Duck hybrids;[21] 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.
It was generally assumed that as the spectacular nuptial plumage of Mallard drakes is obviously the result of sexual selection - most species in the mallard group being sexually monomorphic -, hybrid matings would preferentially take place between females of monomorphic relatives and Mallard drakes instead of the other way around. But this generalization was found to be incorrect.[22]
Note that it is not the hybridization itself that causes most conservation concerns. 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 exist. 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 much 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 Gray Duck's population declined drastically due to overhunting in the mid-20th century (Williams & Basse 2006). In the Hawaiian Duck, it seems that hybrid offspring are less well-adapted to native habitat and that utilizing them in reintroduction projects makes these less than successful.[23] In conclusion, the crucial point underlying the problems of Mallards "hybridizing away" relatives is far less a consequence of Mallards spreading, but of local ducks declining; allopatric speciation and isolating behavior have produced today's diversity of Mallard-like ducks despite the fact that in most if not all of these populations, hybridization must always have occurred to some extent. Given time and a population of sufficient size exists, natural selection ought to suppress harmful allele combinations to a negligible level.
The aforementioned confounds analysis of the evolution considerably. Analyses of good samples of mtDNA sequences give the confusing picture[24] one expects from a wide-ranging species that has evolved probably not much earlier than the Plio-/Pleistocene boundary, around 2 mya. Mallards appear to be closer to their Indo-Pacific relatives than to their American ones judging from biogeography. Considering mtDNA D-loop sequence data,[25] they may have evolved more probably than not 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 paleosubspecies which made up at least the European and W Asian populations during the Pleistocene has been named Anas platyrhynchos palaeoboschas.
As expected, haplotypes typical of American Mallard relatives and Spotbills can be found in Mallards around the Bering Sea.[26] Interestingly, the Aleutian Islands turned out to hold a population of Mallards that appear to be evolving towards a good subspecies as gene flow with other populations is very limited.[25] This unexpected result suggests that reevaluation of the Greenland, Iceland, and NE Canada populations according to molecular and morphological characters is warranted.