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Description
Mallard (Anas platyrhynchos)

The Mallard, probably the best-known and most recognizable of all ducks, is a dabbling duck which breeds throughout the temperate and sub-tropical areas of North America, Europe, Asia, New Zealand (where it is currently the most common duck species) and Australia. It is strongly migratory in the northern parts of its breeding range, and winters farther south. For example, in North America it winters south to Mexico, but also regularly strays into Central America and the Caribbean between September and May. The Mallard and the Muscovy Duck are believed be the ancestors of all domestic ducks.

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. The size of the Mallard varies clinally, and birds from Greenland, although larger than birds further south, have smaller bills and are stockier.

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. 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.

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 fledging. 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. Mallards also have rates of male-male sexual activity that are unusually high for birds. In some cases, as many as 19% of pairs in a Mallard population are male-male homosexual.

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.

Like elsewhere worldwide the invasive alien mallard ducks are also causing severe "genetic pollution" of South Africa's biodiversity by breeding with endemic ducks. The hybrids of mallard ducks 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 worldwide like the yellow billed duck of South Africa. The mallard duck can cross breed with 45 other species and is posing a severe threat to the genetic integrity of indigenous waterfowls. Mallard ducks and their hybrids compete with indigenous birds for resources such as food, nest sites and roosting sites. The drakes (males) also kill the offspring of other waterfowl species by attacking and drowning them.

More info: [link]

Description
Mallard (Anas platyrhynchos)

The Mallard, probably the best-known and most recognizable of all ducks, is a dabbling duck which breeds throughout the temperate and sub-tropical areas of North America, Europe, Asia, New Zealand (where it is currently the most common duck species) and Australia. It is strongly migratory in the northern parts of its breeding range, and winters farther south. For example, in North America it winters south to Mexico, but also regularly strays into Central America and the Caribbean between September and May. The Mallard and the Muscovy Duck are believed be the ancestors of all domestic ducks.

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. The size of the Mallard varies clinally, and birds from Greenland, although larger than birds further south, have smaller bills and are stockier.

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. 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.

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 fledging. 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. Mallards also have rates of male-male sexual activity that are unusually high for birds. In some cases, as many as 19% of pairs in a Mallard population are male-male homosexual.

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.

Like elsewhere worldwide the invasive alien mallard ducks are also causing severe "genetic pollution" of South Africa's biodiversity by breeding with endemic ducks. The hybrids of mallard ducks 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 worldwide like the yellow billed duck of South Africa. The mallard duck can cross breed with 45 other species and is posing a severe threat to the genetic integrity of indigenous waterfowls. Mallard ducks and their hybrids compete with indigenous birds for resources such as food, nest sites and roosting sites. The drakes (males) also kill the offspring of other waterfowl species by attacking and drowning them.

More info: [link]