The American Ornithological Society[2] continues to debate this determination; however, nearly all other authorities consider it distinct based on behavioral,[3] morphological,[4] and molecular evidence.
The green-winged teal was formally described in 1789 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae.
[7] Gmelin based his description on the "American teal" that had been described in 1785 by John Latham in his A General Synopsis of Birds and in the same year by Thomas Pennant in his Arctic Zoology .
The breeding male has grey flanks and back, with a yellow rear end and a white-edged green speculum, obvious in flight or at rest.
It is a common duck of sheltered wetlands, such as taiga bogs, and usually feeds by dabbling for plant food or grazing.
[14] It can be seen in vast numbers in the Marismas Nacionales-San Blas mangroves of western Mexico, a main wintering area.
[17] Though less commonly seen, there are a multiple photographic records from countries in northern South America, such as Venezuela, Colombia, and Ecuador.
[16][19] Within the above associations, green-winged teal commonly inhabit wetland communities dominated by bulrushes (Scirpus spp.
[16][17] Green-winged teal frequently nest in grasses, sedge meadows, or on dry hillsides having brush or aspen (Populus spp.)
[16] Green-winged teal inhabit inland lakes, marshes, ponds, pools, and shallow streams with dense emergent and aquatic vegetation.
These ducks nest in depressions on dry ground located at the base of shrubs, under a log, or in dense grass.
In northern areas of the United States, green-winged teal migrating to wintering grounds appear in early September through mid-December.
At Minto Lakes, Alaska, green-winged teal initiate nesting as early as June 1 and as late as July 20.
[16] In marshes, sloughs, and ponds, green-winged teal select the seeds of bulrushes, pondweeds, and spikerushes (Eleocharis spp.).
This is supported by the observation that in mallard × American black duck hybrids, females of both taxa prefer the sexually dimorphic mallard drakes over the dull-plumaged black duck drakes;[23][24] that the green-winged teal is in some aspects—such as the less contrasting nuptial plumage—intermediate between the common and speckled teal is also interesting to note.
Another possibility[25] is that the American lineage is derived from stray common teals, with the founder effect/genetic drift and/or hybrid introgression phenomena applying as above, only in the reverse direction for the former two.
Still, this would require loss of sexual dimorphism in the ancestors of the speckled teal, but while extremely rare in dabbling ducks, it is not per se impossible.
The close relationship of speckled and green-winged teals suggested by mtDNA data could of course still apply to the taxa in general, not just to sequences in two maternally inherited genes in a few individual ducks (for which it without doubt does apply), but the overall failure of Johnson & Sorenson to seriously take hybridization into account and their small sample sizes and obsolete conceptions of Indian Ocean biogeography do not help at all to resolve the issue,[26] but in 1999, the methodology and interpretation were reasonable enough and in fact, the study was pioneering in many respects due to dense taxon-level sampling and still represents one of the default references for interpreting the phylogeny of the genus.
[27] A firm conclusion cannot be reached at present beyond a tentative rejection of the phylogeny suggested by the mtDNA data.
Nuclear DNA sequence information is required, but may not be sufficient, to resolve the puzzling relationships in the crecca-carolinensis-flavirostris complex of teals.