Anas is a genus of dabbling ducks. It includes mallards, wigeons, teals, pintails and shovelers in a number of subgenera. Some authorities prefer to elevate the subgenera to genus rank. Indeed, as the moa-nalos are very close to this clade and may have evolved later than some of these lineages, it is rather the absence of a thorough review than lack of necessity that this genus is rather over-lumped. The phylogeny of this genus is one of the most confounded ones of all living birds. Research is hampered by the fact the radiation of the two major groups of Anas ? the teals and mallard groups ? took place in a very short time and fairly recently, roughly in the mid-late Pleistocene. Furthermore, hybridization may have long played a major role in Anas evolution, with within-subgenus hybrids regularly and between-subgenus hybrids not infrequently being fully fertile. The relationships between species are much obscured by this fact, and mtDNA sequence data is of dubious value in resolving their relationships; on the other hand, nuclear DNA sequences evolve too slowly to resolve the phylogeny of the subgenus Anas for example. Some major clades can be discerned. For example, that the traditional subgenus Anas, the mallard group, forms a monophyletic (in the loose sense, i.e. non-holophyletic) group has never been seriously questioned by modern science and is as good as confirmed (but see below). On the other hand, the phylogeny of the teals is very confusing. For these reasons, the dabbling duck lineages more distantly related to mallard group (which includes the type species of Anas) than the wigeons should arguably be separated in their own genera. These would include the Baikal Teal, the Garganey, the spotted black-capped Punanetta group, and the shovelers and other blue-winged species. Whether the wigeons, which are very distinct in morphology and behavior, but much less so in mtDNA cytochrome b and NADH dehydrogenase subunit 2 sequences, should also be considered a distinct genus Mareca (including the Gadwall and Falcated Duck) is essentially the one remaining point of dispute as regards the question which taxa should remain in this genus and which ones should not.
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|fledging min.:||50||days||fledging max.:||60||days|
Random disasters and the limited carrying capacity of the fragile tiny islands are the main threats to its persistence. Historic declines on Laysan leading to the near-extinction of the species are attributed to introduced rabbits and more recently the parasitic nematode Echinuria uncinata, coupled with drought. Since the severe range contraction of the species from the main Hawaiian Islands after the introduction of rats, stochastic events that have already occurred include: the accidental introduction of noxious competitors, extreme weather, and disease epizootics. Additional populations on different islands are needed to reduce the extinction risk to small concentrated populations from alien predator introductions, tsunamis, and hurricanes, as the probability that disasters will affect several islands simultaneously is lower. On Laysan Island, brood rearing habitat is probably an important limiting factor. Freshwater seeps with high invertebrate abundance and adjacent dense vegetative cover are used as duckling nurseries. High incidence of duckling trauma suggests these freshwater seeps may become overcrowded. Reproductive success is sometimes related to brine fly (prey abundance) densities which, in turn, are reduced by drought and low water-levels.