| Dabbling ducks | |
|---|---|
 | |
| Pacific black duck (Anas superciliosa) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Anseriformes |
| Family: | Anatidae |
| Subfamily: | Anatinae Leach, 1820 |
| Type species | |
| Anas platyrhynchos | |
| Genera | |
Seetext | |
TheAnatinae are asubfamily of thefamilyAnatidae (swans,geese andducks). Its surviving members are thedabbling ducks, which feed mainly at the surface rather than bydiving. The other members of the Anatinae are the extinctmoa-nalo, a young but highlyapomorphic lineage derived from the dabbling ducks.
There has been much debate about thesystematical status and which ducks belong to the Anatinae. Some taxonomic authorities only include the dabbling ducks and their close relatives, the extinct moa-nalos. Alternatively,[1] the Anatinae are considered to include most "ducks", and the dabbling ducks form atribeAnatini within these. The classification as presented here more appropriately reflects the remaining uncertainty about the interrelationships of the major lineages ofAnatidae (waterfowl).[2]
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The dabbling duck group, of worldwide distribution, was delimited in a 1986 study[3] to include eight genera and some 50–60 living species. However,Salvadori's teal is almost certainly closely related to thepink-eared duck, and other genera are likewise of unresolved affiliation.[2][4] The peculiarmarbled duck, formerly tentatively assigned to the dabbling ducks, is thought to be a diving duck or even a distinct subfamily.[2]
This group of ducks has been so named because its members feed mainly on vegetable matter by upending on the water surface, or grazing, and only rarely diving. These are mostly gregarious ducks of freshwater or estuaries. Thesebirds are strong fliers and northern species are highlymigratory. Compared to other types of duck, their legs are located more towards the centre of their bodies. They walk well on land, and some species feed terrestrially.
"Puddle ducks" generally feed on the surface of the water or feed on very shallow bottoms. They are not equipped to dive down several feet like their diving counterparts. The most prominent difference between puddle ducks and divers is the size of the feet. A puddle duck's feet are generally smaller because they do not need the extra propulsion to dive for their forage.
Another distinguishing characteristic of puddle ducks when compared with diving ducks is the way in which they take flight when spooked or are on the move. Puddle ducks spring straight up from the water, but diving ducks need to gain momentum to take off, so they must run across the water a short distance to gain flight.
Traditionally, most ducks were assigned to either theshelducks, theperching ducks, and the dabbling anddiving ducks; the latter two were presumed to make up the Anatinae. However, the perching ducks turned out to be aparaphyletic assemblage of varioustropical waterfowl that happened toevolve the ability to perch well in their forestedhabitat. Several of these, such as theBrazilian teal, were subsequently assigned to the Anatinae.
As for thediving ducks,mtDNAcytochromeb andNADH dehydrogenasesubunit 2sequence data[2] indicates that they are fairly distant from the dabbling ducks. Themorphological similarities[3] are due toconvergent evolution.
In addition, the genusAnas, as traditionally defined, is notmonophyletic; severalSouth American species belong to a distinct clade which would include theTachyeres steamer-ducks.[2] Other species, such as theBaikal teal, should also be considered distinct.
The following genera are (with one exception) unequivocaldabbling ducks:
The three known genera and four known species ofmoa-nalos all became extinct around AD 1000. They formerly occurred on theHawaiian Islands and were derived from dabbling ducks, possibly even from a close ancestor of themallard:
Subfossil remains of a small, flightless dabbling duck have been recovered onRota in theMariana Islands.[5] These cannot be assigned to a known genus, but probably are closest toAnas. A most bizarre duck-like bird,Talpanas lippa has been found on theHawaiian island ofKauai.[6] Because of its uniqueapomorphies (it seems to have had small eyes high and far back on its head), the placement of thisanatid is likewise unresolved; only dabbling ducks and truegeese are with certainty known to have colonized theHawaiian archipelago.
Another bizarre insular anatine wasBambolinetta from the LateMiocene ofTuscana, then part of the Tuscano-Sardinian insular landmass. Flightless or at least a poor flyer, it instead shows adaptations for wing-propelled diving, occupying a similar ecological niche to that ofpenguins andplotopterids.
Frequently placed into the Anatinae are these genera, whose relationships must be considered uncertain at present:
On the other hand, the following genera, usually considered to belong into the Tadorninae, may actually be dabbling ducks:
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