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Saturday, 3 March 2012

The thorny problem of GREEN-WINGED TEAL identification - the responses

Dave Appleton of Norfolk responded ''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,“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''

Bruce Mactavish, birding in Newfoundland, offered

In St. John’s, Newfoundland we annually have a dozen or two overwintering teal more or less equally divided up between Common Teal and Green-winged Teal. In an exceptional winter like 2010/2011 there were four times more Common Teal (50+ individuals) than Green-winged Teal. Overall there are far more Common Teal occurring in eastern Newfoundland than observed elsewhere in eastern North America. In my 4+ decades of birding in eastern Newfoundland I’ve only once seen a male teal suspected of being a hybrid Common X Green-winged Teal. It had a blurred, dulled out white vertical and horizontal bar. The vertical bar was stronger than the horizontal bar but neither bar was as crisp white as a purebred.

This being said I’ve seen drake Common Teal in St John’s area joining bachelor flocks of dabbling ducks in late May that one would normally presumed bred locally. Did they breed locally???

The teal in the photo could be a hybrid. The gray horizontal stripe is faded compared to the vertical stripe. The white border on the green face patch is suggestive of Common Teal but is actually within range of Green-winged Teal.

Unlike the Alaskan vs Russian coast I think there are few chances for Green-winged x Common Teal to be happening in the North Atlantic''


Another 'Teal' website - http://thebirdguide.com/identification/Eurasian_Teal/teal_hybrid.htm

Nick Lethaby noted ''I don’t think the presence of some yellow rimming around the green on the face is indicative of a hybrid. The pale horizontal bar is definitely suspicious but subtle. I need to look at more bird here. Generally the bird I call hybrids have a more obvious horizontal bar but that doesn’t of course mean that GW Teal show a ‘ghost bar’ like this with any regularity''