Green-Winged Teals
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The Green-winged Teal (GWT, Anas carolinensis) is a common and widespread duck which breeds in the northern areas of North America except on the Aleutian Islands.
It was considered conspecific with the Common Teal (A. crecca) for some time, and the issue is still being reviewed by the American Ornithologists' Union; based on this the IUCN and BirdLife International (BirdLife International, 2004) do not accept it as a separate species at present. However, nearly all other authorities consider it distinct nowadays, based on behavioral (Laurie-Ahlberg & McKinney 1979), morphological (Livezey, 1991), and molecular (Johnson & Sorenson 1999) evidence (discussed by Sangster et al.., 2002).
This dabbling duck is strongly migratory and winters far south of its breeding range. It is highly gregarious outside of the breeding season and will form large flocks. In flight, the fast, twisting flocks resemble waders
While its conservation status is not evaluated by IUCN at present due to non-recognition of the taxon, it is plentiful enough to make it a species of Least Concern if it were; it is far more plentiful than the Common Teal (Carboneras, 1992). It can be seen in vast numbers in the Marismas Nacionales of western Mexico, a main wintering area.
Description
This is the smallest North American dabbling duck. The breeding male has grey flanks and back, with a yellow rear end and a white-edged green speculum (= distinctive wing patch), obvious in flight or at rest. It has a chestnut head with a green eye patch. It is distinguished from drake Common Teal (the Eurasian relative of this bird) by a vertical white stripe on side of breast, the lack of both a horizontal white scapular stripe and the lack of thin buff lines on its head.
The females are light brown, with plumage much like a female Mallard. They can be distinguished from most ducks on size and shape, and the speculum. Separation from female Common Teal is problematic.
In non-breeding (eclipse) plumage, the drake looks more like the female.
Diet / Feeding
It is a common duck of sheltered wetlands, such as taiga bogs, and usually feeds by dabbling for plant food or grazing.
Nesting / Breeding
It nests on the ground, near water and under cover.
Calls / Vocalizations
This is a noisy species. The male has a clear whistle, whereas the female has a feeble "quack".
Relationships
mtDNA data-wise, this species is more closely related to the Speckled Teal than to the Common Teal (Johnson & Sorenson 1999). This would require that sexual dimorphism either was lost in the Speckled Teal or that it evolved in near-identical forms in the Green-winged and Common Teal after the divergence of the Green-winged and Speckled Teal lineages.
Both hypotheses seem rather spurious initially, with the GWT and Common Teal's male nuptial plumage being unique and very complex, and the tendency to gain, not lose, strong sexual dimorphism overwhelming in the dabbling ducks. An alternative explanation given the high frequency of hybridisation in ducks (Carboneras, 1992) would be that the mtDNA of the present-day GWT is originally derived from Spotted Teal females by introgression and thus the molecular data gives a misleading picture of the species' true relationships. 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 (Brodsky et al., 1988, but see also Rhymer et al., 1994); that the GWT is in some aspects - such as the less contrasting nuptial plumage - intermediate between the Common and Speckled Teal is also interesting to note.
Alternatively, the Common Teal might actually be derived from the GWT, with the molecular difference being due to genetic drift or a founder effect in the latter and possibly Speckled Teal introgression in the former. The three teals certainly belong to a superspecies in the teals ("Nettion"); the ancestors of this group were most likely sexually monomorphic Southern Hemisphere forms (Johnson & Sorenson, 1999; note that their "African" distribution includes Bernier's Teal taxa which like many Madagascar taxa is of Indo-Australian origin).
Still another possibility - and perhaps the most likely one -, 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 Speckled-GWT relationship suggested by mtDNA data could of course still apply to the taxa in general, not just to sequences in 2 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, 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 pyhlogeny of the genus.
It is worthy of note that the post-copulatory displays of the Common and GWT are identical, but those of the Speckled Teal have some additional elements (Johnson et al., 2000).
All in all, 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.
Copyright: Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia.org
Diet / Feeding:
The Common Teal usually feeds by dabbling, upending or grazing; it may submerge its head and on occasion even dive to reach food. In the breeding season it eats mainly aquatic invertebrates, such as crustaceans, insects and their larvae, molluscs and worms. In winter, it shifts to a largely granivorous diet, feeding on seeds of aquatic plants and grasses, including sedges and grains. Diurnal throughout the breeding season, in winter they are often crepuscular or even nocturnal feeders.
Ducks generally feed on larvae and pupae often found under rocks, as well as aquatic animals, plant material, seeds, small fish, snails and crabs.
Feeding Ducks ...
We all enjoy ducks and many of us offer them food to encourage them to come over and stay around - and it works! Who doesn't like an easy meal!
However, the foods that we traditionally feed them at local ponds are utterly unsuitable for them and are likely to cause health problems down the road. Also, there may be local laws against feeding this species of bird - so it's best to check on that rather than facing consequences at a later stage.
- Click here to find out which foods to feed them that will offer the nutrition they need to survive a cold winter and remain healthy
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