IDENTIFICATION
ARTICLES
Identification of Green-winged and Eurasian Teal.
Green-winged Teal (Anas carolinensis) is a regular visitor to Hawai'i, mainly during the period between October and April, with a few records from late spring and summer. It is a common breeding species on the continental United States and it is therefore not surprising that the species occurs so frequently in the State. The species has recently been split (2001) by the BOURC from Eurasian Teal (Anas crecca) which occurs commonly across Europe and Asia and was also formally split by the AOU in 2002. The Eurasian Teal is a far rarer, less-than-annual visitor to Hawai'i, and like the Green-winged Teal, tends to occur during the winter months.
Although adult drakes are easily identified the females and juveniles of both species are difficult to separate and identification features for these plumages are poorly known and still evolving. The following short article will detail identification features for both species including for female and juvenile plumages, and although not every individual bird will be identifiable it is hoped that at least some of the often-ignored "plainer" plumages will be scrutinised more closely to determine which species is involved.
Undoubtedly many individuals in female and juvenile plumage simply are recorded as Green-winged Teal, as this is the more likely species, but of course it is almost certain that every year Eurasian Teal occurs but are not identified, unless perhaps the birds are consorting with an adult male Eurasian.
Drake Green-winged and Eurasian Teal
Drake Teal of both species are usually easily identified in adult plumage by the vertical white stripe on the front of the flanks on Green-winged and the horizontal white line on the inner webs of the outer scapulars, appearing as a white line above the flanks on a resting bird, in Eurasian. Both species have a horizontal black stripe which is formed by the outer webs, which appears at rest above the flanks. There are however further differences which are less obvious and often overlooked in favor of the "white line" identification.
The head pattern of the two species differs in that on Green-winged Teal the buff surround to the eye is limited to the underside of the green eye patch (and is often narrower than in Eurasian) and perhaps a little on the loral area and before the eye, whereas on Eurasian the buff surrounds the entire eye.
Both species have yellow undertail coverts bordered by black but in Green-winged the yellow is often a richer golden color than in the other species, which tends to be more pale lemon in tone.
The breast of drake Green-winged Teal is also often much more richly colored with a deeper pinky wash compared to the buffy coloration shown in Eurasian.
In a flying bird the mid-wing bar formed by the broad tips to the greater coverts is white in Eurasian but cinnamon-buff in Green-winged.
At rest a Green-winged Teal in amongst a flock of Eurasian may appear much darker and this could be due to the denseness of the vermiculations of the feathering, particularly on the flanks, back and mantle. In Eurasian the vermiculations are fairly evenly spaced with dark and light vermiculations, on Green-winged these are much more tightly packed and often merge into one another as plain gray feathering, thus giving an overall impression of a darker plumage.
Drake Eurasian Teal on flood between Kekaha and Waimea, Kaua'i on February 11th 2005.
Photograph © by Jim Denny
Female and immature Green-winged and Eurasian Teal
As already stated not every individual will be identifiable, and not all may show all the features described and so great care and caution should be employed before a final identification is made.
Obviously both Green-winged and Eurasian Teal in female and immature plumages are very similar to each other but Green-winged may appear more sepia-toned or gray overall whereas Eurasian often appears buffier in coloration.
The head patterns of Eurasian are usually rather indistinct and plain and lack contrast, whereas in Green-winged the head pattern is often distinct and can even sometimes recall Garganey. In Green-winged the eye stripe and crown may be dark brown which highlights the supercilium, which is pale. Some birds show a dark ear-covert smudge and this can emphasize the pale upper cheek stripe, which in birds without the dark smudge can not look as bright.
Sometimes the loral area has a pale spot, far more pronounced than in Eurasian and the throat is often very pale or almost white. The whole face in Green-winged is often less marked with streaks or freckles than in Eurasian too.
The upperwing of Eurasian has a greater covert bar which is usually white sometimes washed cinnamon whereas in Green-winged the bar is evenly and richly cinnamon-buff in coloration. On Eurasian the cinnamon color wash is usually restricted to the inner third of the hand, whereas in Green-winged it covers 80% or more. The tips of the outer secondaries are usually broader in Green-winged than Eurasian too.
The tightness of the mottling on the breast and fore-flanks has also been cited as a character for separation between the two species, with Green-winged generally showing smaller and more compact patterning, giving a darker impression overall, especially when combined with the browner background coloring (rather than gray in Eurasian).
The bill in juveniles shows a large yellow or pinky-orange color on the lower mandible and base of the upper mandible in Eurasian but Green-winged shows far less coloration and may even be all-dark or with color restricted to the lower mandible. Bills of females are similar but appear to be a little more variable (Millington 1998).
Of all the features mentioned for female and immature birds the most conistent and apparently crucial feature is the coloration of the greater coverts, and it is probably best to ensure this feature is present first before using the other features as back-up to an identification.
Hybrids have been recorded on several occasions, in Europe, the States and Hawai'i and it seems likely that although drakes are identifiable as hybrids, females and juveniles would probably be unidentifiable.
So next time you find a female-type Teal don't just pass it off as Green-winged because it may just turn out to have come from a little further afield!
Green-winged and Eurasian Teal Taxonomy
The BOU following the August 18, 2000 recommendations of the British Ornithololgical Union
Records Committee Taxonomic Sub-committee (BOURC's TSC) and the Taxonomic Advisory committee of the Association
of European Rarities Committees (AERC TAC) - has spilt Common Teal (Green-winged Teal) (Anas
crecca) into two seperate species: Eurasian Teal
(Anas crecca).
Range: Nearctic region; winters to Africa, India and SE Asia and race (nimia) - range Aleutian Islands. Green-winged Teal (Anas carolinensis) - Range North
America; winters to Mexico and West Indies (British Ornithological Union Records Committee 27th Report 2001.Ibis
Vol.143: 171-175). Andrew Kratter, who is a member of the AOU Committee on Classification and Nomenclature (the
Check-list Committee), wrote the following regarding the taxonomic issues and the opinion of at least one member
of the Check-list Committee on the information that he would like to see, and or revisit before making a decision
to have the AOU follow the BOU's lead: "Johnson and Sorenson (Auk 116:792-805, 1999) certainly present good
evidence that crecca and carolinensis are separate species. The sequence divergence (5.8%) is certainly large for closely related taxa
in North America (but bird "species" in Amazonia may approach this level of divergence), indicating that
these two taxa have been evolving in genetic isolation for quite some time. However, there is no rule of thumb
for how divergent two taxa have to be considered separate species, at least for those who follow the biological
species concept. The point at which reproductive isolation arises is arbitrary along the continuum of genetic divergence.
Conceivably, species could be reproductively isolated on the basis of a single base pair substitution, which would
be almost undetectable by today's methods of sequencing only very small parts of the genome (result: two species
in the BSC, maybe something like Anas cyanoptera
and discors, Blue-winged and Cinnamon teals).
On the other hand, two populations may be genetically isolated for long periods and
only accumulate neutral substitutions that have no bearing on whether they are reproductively isolated (one species
in the BSC). But with 5.8% sequence divergence, there is definitely a strong chance that some of this divergence
will have bearing on reproductive isolation.
There is also a problem of having paraphyletic taxa, because A.
flavirostris (Speckled Teal of South America) and carolinensis are more closely related than crecca
and carolinensis. However, I am not uncomfortable
with some paraphyly at the species level. Such a situation could arise when you have two genetically isolated populations
(A & B) , which are not reproductively isolated (e.g., Carolina Chickadees). Let's say that one of these populations
(A) gives rise to a new population (A1) that becomes genetically and reproductively isolated from A (as fate would
have it by a single base pair substitution that changes molt schedule). Meanwhile, A and B still are having only
neutral substitutions that have no bearing on reproductive isolation. A1 and A are thus sister taxa, but using
a BSC, A and B are still the same species. Two paraphyletic species have arisen. To me, the evidence for lumping
crecca and carolinensis was probably inadequate by today's standards, but that's the status quo. Given the arbitrary
nature at which reproductive isolation arises in regards to the continuum of sequence divergence, most of us in
the committee would like to see some new published information on frequency of hybridization, and other characters
that have bearing on reproductive isolation (molt schedules, displays, timing of breeding, etc) from areas near
parapatry before we make a decision. Maybe we only have to revisit the old literature. I am sure that we shall
deal with this by the next supplement, scheduled for July, 2002."
References:
CRAMP, S. et al. 1977. Handbook of the Birds of Europe, the Middle East and North Africa. Vol 1. Oxford.
MADGE, S. and Burns.H. 1988. Wildfowl. London.
MILLINGTON, R. 1998. The Green-winged Teal. Birding Hawaii 11/1. pp. 430-434. Norfolk.
PALMER, P. 1999. A hybrid Green-winged Teal? Birding World 12/9. p.377. Norfolk.
SCOTT, M. 1999. Identification of female Green-winged Teal. Birding Hawaii 12/2. p.81. Norfolk.
Christian Melgar, West Sussex, UK. 2001.
