Bob,
The Great Skuas, all three, were in wing molt with the inner primaries being replaced. Those short inner primaries produced a notch in the wing that one might assume were "missing" feathers. There might have been one feather or so dropped, hence "missing" only in the sense that the replacement feather was in pin and not visible. But I don't think that's what you meant.
I think this is simply a misunderstanding and only a technicality in the context of your newspaper article. There were lots of "missing" feathers on the Great Skuas (wing coverts mostly), but that was all due to normal molt.
The South Polar Skuas, by contrast, were both finished or nearly finished (2nd bird) with wing molt, a schedule that matches birds in their second plumage cycle and older among the big skuas. The difference in wing shape and molt that we saw--the Greats looking ragged and with notches in the wings versus a smoother looking appearance across the wing on the South Polars--was striking.
This difference is most marked between older birds of both species, which have breeding seasons offset by about six months. The only complication is that birds in their first year undergo a wing molt that more or less coincides with the timing of older birds of the *opposite* species. A first-year South Polar could have a molting wing like our Great Skuas in September. Confusing. Thankfully, our Great Skuas showed obvious gold-buff streaks on their upperparts and breast, confirming their identity. Likewise, a Great Skua in its first year, when they mostly lack the definitive gold-buff streaks, would have ragged wing molt about the time older South Polar Skuas do when we see them in summer. Without ageing birds, one cannot confidently identify them by molt schedule alone. This is why the status of skuas in the Gulf of Maine remains a work in progress. We do know that Great Skua is a post-breeding migrant, appearing mid to late August and into the fall; most summer skuas are South Polar. Without definitive photographs or specimens, we don't know with confidence that this pattern has changed, even though older references before the knowledge that South Polar occurred suggested Great Skua also visited in summer.
A paper in British Birds (June 2013 issue) by Newell, Howell, and López-Velasco discusses molt differences between South Polar and Great Skuas as a possible aid to identification. I don't have a link to the paper itself, but here is a link to the issue of British Birds:
http://www.britishbirds.co.uk/latest-issues/british-birds-june-2013
My photos for 3 of the 5 skuas start here (then go back for the others):
http://www.flickr.com/photos/lrbevier/9826630173/
Doug Hitchcox got them all (again, use right arrow to go back through the others):
http://www.flickr.com/photos/dhitchcox/9766380816/
I should also note that most current classifications recognize 4 species of large skuas, not just two--Great Skua breeding in the Northern Hemisphere and three species breeding in the Southern Hemisphere (South Polar, Brown, and Chilean). Only two species have been confirmed in our region, but a possible Brown Skua was photographed off Nova Scotia. Something to shoot for next year!
Louis Bevier
Fairfield
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