Black Scoter is common in Japan and Korea, regular in north and east China and only a few hundred miles out of range in Hong Kong.
Common Scoter is more than 5000 miles out of range in the opposite direction to its normal flight and has never previously been recorded in the Pacific or North America.
As this bird is one or the other, and nothing else, Black Scoter is so much more likely than Common Scoter that it seems unnecessary to debate which it is. We regularly record species in Hong Kong with a distribution like Black Scoter, but never like Common Scoter.
Looking through the images of Common Scoter on the Birdguides website, two features seem to regularly occur with female Common Scoter. One is a distinct dark cheek stripe stretching up from the chin towards the cap. The second is that the dark cap does not go all the way down the nape but ends around the middle of the nape. This is caused in a side-on view by the dark cap gradually narrowing to a point as it goes down the nape. The Mai Po bird does not appear to show either of these features. Unfortunately, I cannot reproduce the photos here but Martin Garner's two diagrams show the differences he suggests between the two species
As John says, from Hendrix's photos, the bird is closer to Black Scoter. There is no evidence to suggest it may be a Common Scoter.
Taking distribution and these features together, it is surely stretching possibilities too far to suggest this could be a Common Scoter. There has to be a point at which you say, no, Common Scoter is so unlikely that I can ignore it, even for a first record.
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Last edited by wgeoff at 5/10/2008 08:48 ]
