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Thread: Variability in North American Green-winged Teals

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    Default Variability in North American Green-winged Teals

    I had a look at the drake Green-winged Teal in Maldon today and noticed that it is the same bird as recently at Alton Water in South Suffolk. Although it has striking pure white vertical white foreflank lines, it has a hint of a white horizontal scapular stripe and golden-buff edgings to the lower part of the green facial stripe. Last autumn, a drake at caerlaverock WWT shared similar features.

    Now is this within the natural variation of carolinensis or is it evidence of intergradation? Keith Viinicombe has kindly trawled the net for me and found similar examples in North America.

    Of course, this drake is much more convincing in plumage to last year's undoubted hybrid at Connaught Water, Epping, but is it really pure?

    David Acfield's selection of images are posted below

    GWTeal5.jpgGWTeal5.1.jpg

    And here are Chris Baines' shots of the Alton Water drake

    IMG_6959.jpgIMG_6920.JPGIMG_6909.JPG

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    On my UK400 Club blog of the same subject, I have added a link to an excellent article that David Sibley has written on Green-winged Teal/Common Teal combinations. In his book, this bird would go down as a hybrid....

    Thanks to Alan Tilnmouth for correspondence

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    For what it's worth, the G-w Teal at East Chevington (Northumbs) is currently paired up with a female teal, which is presumably Eurasian. So there may be more hybrids by the end of the summer.

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    Hi Lee,

    For me these are perfectly good Green-winged Teals, or at least the two features you note as perhaps being indicative of an intergrade are in fact perfectly acceptable for pure Green-winged Teal.

    When you asked about the Connaught bird last year I pointed out that a pale lower border to the green facial area below and behind the eye is well within normal variation for Green-winged Teal – in fact although there is some variation in the extent and prominence of this feature the birds you are querying do not seem to me to be at all unusual in this respect.

    The hint of a pale horizontal stripe is, I believe, also well within normal variation for pure Green-winged Teal. I suspect its appearance is partly dependent on light as it appears to vary between different photos of the same individual in some cases. You’ve noted that Keith has found photos of birds in North America showing this feature and I’d support that – it seems quite frequent indeed.

    I don’t think these birds are intergrades, but pure Green-winged Teals. However if they are intergrades then it cannot be as you suggest elsewhere, “generations of European birds are hybridising following the vagrancy of some pure North American individuals”. If it were that then hybrids would be mating with Eurasian Teals in the main and would be closer in appearance to Eurasian Teal than Green-winged Teal. The only way the intergrade theory can possibly be the answer is if there is genetic introgression from vagrant Eurasian Teals in North America to large parts of the North American population of Green-winged Teals such that many of the Green-winged Teals there are in fact intergrades, and these intergrades are crossing the Atlantic. But I think the simpler explanation is that they are pure Green-winged Teals and this is normal variation.

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    Quote Originally Posted by LeeEvans View Post
    I had a look at the drake Green-winged Teal in Maldon today and noticed that it is the same bird as recently at Alton Water in South Suffolk.
    Why do you say that this is the same bird? It certainly doesn't look like the same bird to me based on the photographs that you have posted here, and others that I have found elsewhere on the web. The vertical white stripe on the fore flanks is broad and of fairly even width in the photos of the Alton Water bird, but much narrower, tapering towards the lower end, and 'more messy' on the Maldon bird (in this respect it is more similar to last winters Connaught Waters bird). It is possible that the vertical stripes on the Alton Waters bird have been emphasised slightly because the photos are slightly out of focus or lower definition, but it doesn't look like this is the case.



    Quote Originally Posted by LeeEvans View Post
    is this within the natural variation of carolinensis or is it evidence of intergradation? Keith Viinicombe has kindly trawled the net for me and found similar examples in North America.
    An internet search for photos of Green-winged Teal taken in America will produce a lot of photos of otherwise 'normal' Green-winged Teal that have a faint and/or narrow horizontal white line along the lower scapulars - so I completely agree with Dave in that if this does mean that there are Eurasian Teal genes in these individuals, there must be a lot of introgression of Eurasian Teal genes into the North American Green-winged Teal population (or perhaps this is a feature that has been lost in the American population).
    The vertical white lines on the fore flanks can also be seen to be highly variable, with some individuals having only weak vertical stripes.



    Quote Originally Posted by LeeEvans View Post
    course, this drake is much more convincing in plumage to last year's undoubted hybrid at Connaught Water, Epping, but is it really pure?
    Perhaps you mean that it is more convincing that the probable/almost certain hybrid at Connaught Waters?
    I'm sorry, but without conclusive genetic analysis having been carried out, or a complete understanding of all of the potential variation of Green-winged Teal, I don't believe that the Connaught bird can be said to be an "undoubted hybrid".
    It might seem unlikely that a pure Green-winged Teal would show both a pale horizontal line on the scapulars, and weak vertical fore flank stripes that weren't even on both sides - but do we KNOW that pure individuals can't look that way? I would expect that any individuals that looked the same on the other side of the Atlantic would also be assumed to be hybrids. I do agree that it wouldn't be safe to accept the record as a pure bird though (too many reasons to doubt this).



    Quote Originally Posted by LeeEvans View Post
    On my UK400 Club blog of the same subject, I have added a link to an excellent article that David Sibley has written on Green-winged Teal/Common Teal combinations. In his book, this bird would go down as a hybrid....
    The problem is that any teal that doesn't precisely fit with our idea of what each species (or subspecies) should look like is generally assumed to be a hybrid. While it is possible that this may be the case, it is also possible that it is normal variation - perhaps before the ancestral form was more like Eurasian Teal with a white stripe on the lower scapulars and no vertical white bar, and these genetics still show up occasionally in Green-winged Teal.

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