Since the discovery of this scoter last year, there has been some discussion about whether the bird can be safely identified as Black Scoter, and whether Common Scoter can be ruled out. The ID as Black Scoter (
Melanitta americana) is based largely on range, as this is the form that breeds in eastern Siberia (and America) and winters in the Pacific (including northern China). Common scoter (
Melanitta nigra) breeds to north-central Siberia and winters in Europe. The two were treated as one species until recently.
The debate for the HK bird is whether it is possible to seperate female/immature Common and Black Scoter in the field. This issue is addressed in the recent book 'Frontiers of Birding' by Martin Garner, who suggests that the two can be separated. Checking internet photos I agree. Note that the following is based mostly on photos - I have limited experience of common scoter and have only seen one black before the HK bird. I am basing ID on Hendrix's photos and photos by Martin Hale at:
http://orientalbirdimages.org/se ... lt&Bird_ID=2800
The book suggests the two species can be separated by the following charaters typical of black:
- - Lumpier bill, often with slightly swollen base and prominent hooked/arched nail. The HK bird has a very prominent nail (bill tip). The bill is not as lumpy as some Black scoter but is fairly short and deep-based, not long and triangular as on Common Scoter.
- - Typically steeper forehead and squarer head shape. HK bird has a rather square-looking head (see Hendrix first photo). Common seems to show a rounder head, peaking just behind the eye.
- - More dark patterning on sides of nape. Although the HK bird shows the dark pattern narrowing to the base of the nape, this seems to be in the range of Black. Checking internet images, the dark cap on common seems to be more horizontal, often reaching the top of the bill, level through the eye and then back to the nape. The HK bird shows a gentler curve from the bottom of the bill and fairly broad on the nape.
- - Dark cap may end as a squared-off or broad rounded line on the nape, not tapered as in Common. The HK bird seems to show a squared-off end to the dark cap (see second photo of bird head-flapping), although the cap does narrow to the base of the nape. The end of the cap on Common often seems to almost meet across the back of the nape.
- - 10% of adult females show extensive yellow on bill. No yellow on bill of HK bird, but this does not rule out either species, especially on a first-winter female (which I think is the case for the HK bird)
- - Cheeks tend to be cleaner with a less obvious dark vertical cheek mark. Some of Hendrix's photos show a hint of the dark cheek-mark, but this is not obvious. This seems to be a variable feature in both species, which may depend on light conditions. The HK bird is probably in the range of variation for either species.
Other features mentioned in the book (based on observations of males, but probably also applicable to females) are a tendency for black to sit higher in the water and cock the tail more often. The tail may also be shorter. In these respects, the HK bird fits better with Black Scoter.
Overall, I think the characters of the HK bird fit better for Black Scoter than Common. This is also the more likely species based on range. I would be happy to hear comments from others, and any additional photos may help establish ID (even, for example, photos from the rear which show the exact nape pattern). I think the bird should be possible to ID - it would certainly be a shame to dismiss this as 'Scoter sp.' unnecessarily.
