Cory's Shearwater Calonectris diomedea borealis
"Scopoli's" [Cory's] Shearwater Calonectris diomedea diomedea
Compared to borealis, Scopoli's appears smaller-headed and slimmer-billed with narrower wings. However, the go-to field mark is the underwing pattern. Specifically, on Scopoli's, the white on the wing linings bleeds well into the underside of the primaries. Note this pattern in the Scopoli's shown above, as well as the subtle structural differences. In borealis, the dark primaries contrast rather strongly with the white wing linings. The above bird is a nice example of Scopoli's [Cory's] Shearwater, currently treated as a subspecies of Cory's by the AOU but may be destined for full species status in the near future. Borealis can show some bleeding of white onto the primary bases but the extent of variation is still, as far as I can tell from my sources, being worked out. This was the only Scopoli's Shearwater identified with certainty on our three boat trips.
Audubon's Shearwater Puffinus lherminieri
Black-capped Petrel Pterodroma hasitata
Over the past few years Steve Howell, Brian Patteson, and others have been documenting the variation in the Black-capped Petrels of the Gulf Stream. They vary most notably in the extent of black on their faces/caps, currently being categorized into "white-faced," "dark-faced," and "intermediate" birds. The white-faced and dark-faced birds appear to differ slightly in seasonal distribution, molt timing and may in fact represent different breeding populations. Could there be a cryptic species in there? Perhaps. If I have some time I may devote a blog post to the variation in BCPE that we noted on our trips - and we certainly had a diverse sampling. I've only posted my best few photos above, but I have many shots of white, dark, and intermediate birds.
Band-rumped Storm-Petrel Oceanodroma castro
Band-rumped Storm-Petrel is one of the reasons I was so glad to get down to Hatteras for these trips since so much has come to light regarding this species complex over the past few years. Still, more questions remain than answers. You may have noticed that the last bird is not in wing molt while the others quite obviously are. More on this in a future post, which will contain more photos and analysis of BRSP.
Leach's Storm-Petrel Oceanodroma leucorhoa
We had a nice handful of cooperative Leach's through the weekend, contrasting well with the Band-rumps. By far the best way to pick out a different storm-petrel from the Wilson's in the slick is to simply observe flight style naked-eye. The other species will just "pop" when they appear once you've gotten down the Wilson's flight style.