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The surface-feeding, dabbling, or similarly described ducks are a group of about thirty-six species of mostly freshwater ducks that occur throughout the world. Many of them are temperate or arctic-breeding species that nest on dry land near freshwater ponds, marshes, rivers, or similar rather shallow bodies of water. Associated with this breeding habitat are their adaptations for foraging by "tipping-up" rather than by diving for food, an ability to land and take off abruptly from small water areas or land, and a moderately good walking ability but reduced perching capabilities as compared with perching ducks. Also unlike perching ducks, iridescent coloration on the wing is limited to the secondary feathers, or in rare cases is lacking altogether.
The surface-feeding ducks are among the most abundant and familiar of all North American ducks and include such popular sporting species as mallards, pintails, wigeons, and various teals. They range in size from less than a pound to more than three pounds and are among the most agile of waterfowl in flight, relying on maneuverability rather than unusual speed to elude danger. The number of North American breeding species is somewhat uncertain, but is at least nine. Additionally, the European wigeon very probably nests occasionally in continental North America, the Baikal teal is possibly a very rare nester, and the Bahama pintail breeds in the West Indies. Further, the "Mexican duck" is often considered to be a separate species from the common mallard, as are the populations called the Florida duck and mottled duck, so these might also be added, bringing the possible total to fourteen. Beyond these, the falcated duck is recognized by the A.O.D. (1957) as belonging on the list of North American birds although there is no evidence for breeding, and in recent years there have been several sight records for the garganey, as well as an occurrence of the Chinese spot-billed duck (Anas poecilorhyncha) on Adak Island (Byrd et al., 1974). Some of the records of falcated duck, Baikal teal, and garganey may well have been the result of escapes from captivity, but it seems likely that others of them represent wild birds, and thus these species are included in this book.
In most respects, the surface-feeding ducks closely resemble the perching ducks in their anatomy and biology, but differ from them in that they are nearly all ground-nesting species that are ill-adapted for perching. Although considerable diversity in bill shape exists among the surface-feeding ducks, most biologists now agree that recognition of a single genus (Anas) is most representative of the close relationships that exist among these species, rather than maintenance of the traditional separate genera for the shovelerlike ducks, the wig~ons, and other subgroups. Similarly, it is quite clear that recognition of separate species of Old World and New World green-winged teals and species recognition for the endemic Mexican, Florida, and Gulf coast populations of mallards are not in keeping with the modem species concept of potentially interbreeding natural populations. Although such changes force some modifications of traditional vernacular names of these populations, these disadvantages seem minor compared to the distortions of natural relationships forced by the retention of traditional nomenclature.