The Green-winged Teal (known as Common Teal in English-speaking parts of Eurasia) is currently considered a single species by the AOU, but two subspecies are distinctive in adult male plumage and are split into two species by many authorities.
- Green-winged Teal (American) – Anas crecca carolinensis
- Common Teal (Eurasian) – Anas crecca crecca ((Common Teal nests in the Aleutian Islands, Alaska, and birds there and in Siberia average larger than those in Europe (which are the same size as American Green-winged Teal). Therefore, Common Teal on the Pacific coast, which presumably come from Siberia, often look slightly larger than their Green-winged flock-mates. These larger birds were formerly separated as the subspecies A. c. nimia, but variation is broadly clinal and that subspecies is no longer recognized.))
Common Teal is a rare visitor to North America, occurring in small numbers each winter along both coasts but most frequent in the north and much less frequent in the far south. It is extremely rare inland. Records are strongly clustered in spring (March-April) but this presumably reflects the fact that males in eclipse (non-breeding) plumage are essentially unidentifiable in the fall, and are difficult to pick out of the large flocks on the wintering grounds. They are found as they make their way north (now in full breeding plumage) with relatively small numbers of teal moving along the coast.
The most conspicuous difference in males is the presence of a horizontal white stripe along the lower scapulars on Common Teal (absent on Green-winged) and the presence of a vertical white bar on the side of the breast of Green-winged (absent on Common). There are other small differences outlined below, but most or all of these are variable and seem less reliable… or maybe the white stripe just seems reliable because that’s how we define a Common Teal (more on that below).
First, it’s critical to understand the feathers that are involved, and how the arrangement of feathers affects the appearance of the field marks. Here is a Green-winged Teal with feathers fluffed to show the arrangement.
The flanks are gray with fine barring, but it’s impossible to make out individual feathers. These flank feathers can be moved up or down (see below) to overlap more or less of the wing. Just above the flanks we can see a little of the bird’s wing – from front to back the darker gray coverts on the leading edge of the wing, a band of cinnamon formed by the tips of the greater coverts, the iridescent green of the secondaries, and white tips on the secondaries. On the bird’s back the brownish-gray feathers are the scapulars, which are relatively long and easy to pick out as individual feathers. Behind the scapulars the longer feathers the same color are the tertials. Finally, just below the scapulars is a band of gray feathers (I’ve enhanced the contrast to make them more obvious here). These are the feathers we need to focus on. ((I’ve realized as I paint that I don’t know what these feathers are. They seem to be separate from the scapulars, not just a row of lower scapulars… but that’s another research project for another post.))
Identifying the subspecies
On this Green-winged Teal these “lower scapulars” are gray with a very narrow and inconspicuous white edge and black lower border. On Common Teal these feathers are clean white with a black lower border. The broader white stripe on Common Teal continues rearwards onto the lowest tertial. That’s it. Because these “lower scapular” feathers can be overlapped by the flanks (from below) or the scapulars (from above) depending on the bird’s mood, the white stripe of Common Teal can be obvious or nearly absent.
Besides the obvious white stripes, other differences between these subspecies are listed here, but only the first two on the list seem to be obvious and consistent enough to be useful. The others are merely tendencies and only suggestive of identification.
- white lines on face more complete and more conspicuous on Common
- breast paler and grayish, less buffy, on Common
- head paler red-brown on Common
- tertials more contrastingly marked on Common
- flanks paler overall with coarser barring on Common
- pale band between black undertail coverts and gray flanks broader and paler
- Iridescence of eye stripe may be sometimes more blue-purple on Common (vs green on Green-winged)
These two subspecies interbreed freely where their ranges overlap, but their ranges barely overlap, so intergrades are rare. Intergrades are probably about as frequent as pure male Commons in North America, or maybe a little more frequent, but tend to be overlooked or simply not reported.
Intergrades can show various combinations of features. Many look intermediate in both of the parental white stripes as shown above, but others can express one white stripe fully while showing only a hint of the other. I have seen a few individual teal showing neither of the white stripes and these might be intergrades as well. Among the other features described above (head pattern, etc) the differences are subtle, and it can be impossible to judge intermediacy, but intergrades usually seem to show a mixture of features typical of both parents rather than intermediate features.
One male in Concord, Massachusetts on 25 Mar 2011 showed the full white stripe of Common, with no trace of the white bar of Green-winged, and also showed obvious white lines on the face and a grayish breast. But it’s head was conspicuously darker than any of the 50 or so Green-wingeds present, and it showed blue/purple iridescence behind the eye (not typical of either subspecies). Was this actually an intergrade that just happened to show a Common-like white pattern?
A small but significant percentage of Green-winged Teal show a reduced white vertical bar on the breast-sides (shown below, perhaps 10%, depending on how “reduced” is defined). This is probably too frequent to be attributed to intergradation, but an individual that also shows slightly increased white on the scapulars, or another feature tending towards Common Teal, might be suspect.
By using a single plumage feature (white stripes) to define the subspecies and intermediates, we are merely taking the easy route to categorizing them. The true ancestry of these birds may be impossible to determine by plumage, but we should take care to study all the plumage features and try to get a better understanding of variation.
Gillson, G. 2004. Common Teal: Eurasian and American Green-winged Teal and hybrids: an identification challenge. http://thebirdguide.com/identification/Eurasian_Teal/teal_hybrid.htm – A detailed discussion of intergrades in Oregon, with photos.