I'm game for Loch Ness. It is always advisable to leave birds unidentified when we can't get the goods, and I'd like to see more "spuhs" on lists. That said, there are clues in Derek's photos that probably tip this safely into the American Golden-Plover basket. Unidentified is certainly a respectable position to take, however.
Although a lot of emphasis is placed on subtle structural differences among the three similar golden-plovers, there are also some important plumage differences detectable at long distance and in fuzzy photos. The pattern of white down the neck and sides differs in notable ways that, although mentioned in field guides, is not stressed in the ways that differ most usefully. The white neck on the Scarborough bird best fits American Golden-Plover, which shows a broadening white line down the neck terminating in a noticeable bulge at sides of the lower breast. This white is then cut-off by the black underparts along the bottom edge of the folded wing. This pattern is perhaps best seen in Derek's images here:
https://www.facebook.com/Freeportwildbird/photos/a.1063941590302461.1073741846.198877036808925/1063941603635793/?type=3&theater
https://www.facebook.com/Freeportwildbird/photos/a.1063941590302461.1073741846.198877036808925/1063941663635787/?type=3&theater
On Pacific G-P, the white is narrower down the neck, doesn't show the broadening bulge like the Scarborough bird, and either shows the white continuing unbroken below the wing to the flanks or is, more typically, occluded by a black spur (or bulge) along the lower breast near the forward part of the wing with white continuing behind that below the wing to the rear flanks and undertail. Pacific G-P has a subtly longer bill and subtly longer legs proportionately [esp. the tibia] and longer primary projection, but these are so close and overlapping that distance and blur would distort or obscure them. Even impression of a longer bill is unreliable here. European likewise has white continue down the neck and sides in a pattern different than the Scarborough bird.
Molting American Golden-Plovers, especially females, will show the pattern presented by the Scarborough bird. These birds also gain the black in the center of the breast and belly FIRST so that the rear flank and undertail often remain white late into spring (or the black dribbles down the midline of the vent and crissum where not seen in profile). Adult males are the ones that show solid black along the rear rear flank and undertail.
I should say that although the gross difference in white down the flanks was long known among the three golden-plovers, the key difference in *pattern* between Pacific an American was first pointed out to me in the early 1990s by Killian Mullarney (see his guide to Birds of Europe where this is shown well). I had taken to him for evaluation a video tape copy of a bird filmed in Delaware and first reported as European Golden-Plover. Several of us thought Pacific Golden-Plover more likely but we lacked good characters to use, including the confusing pattern of black on the bird's underparts (I looked through all the similar American, European, and Pacific G-P specimens available to me then). The video was also somewhat blurry and vague; so we had to work with a similar Loch Ness monster. Killian provided the key insights. That Delaware bird has since been accepted as one of the few East coast records for Pacific G-P, Maine having one of the other records, a bird collected in fall and identified by Jonathan Dwight (published by Arthur Norton). Unfortunately, we have not located that specimen and Maine's record resides somewhat in limbo. There is also a record of Pacific Golden-Plover from Massachusetts from late April to early May (a bird showing a neat white trim from neck sides down through to the flanks). So, it is definitely a good idea to take care with spring golden-plovers here.
Louis Bevier
Fairfield
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