Boyd's Sheawater Puffinus boydi - Cape Verde Islands, March 2009. Vaughan Ashby.With the forthcoming Brookline Bird Club Extreme Pelagic scheduled for July 18th, this week seems like a good time to reflect on the possible species, especially within the small black-and-white shearwaters group. Recent BBC pelagics have recorded Audubon's with some regularity in the deeper warmer waters off Massachusetts. It could even be described as 'expected' on the July and August pelagic trips. Of course, the well documented Barolo's Shearwater (aka Macaronesian or Little Shearwater) on August 25th, 2007 was a huge find and opened up the pathway to the more extreme possibilities from further afield - Barolo's closest known breeding range is in the Azores.
When Vaughan Ashby sent me some images of Boyd's Shearwaters (aka Cape Verde Little Shearwater) taken in March 2009, I was truly taken aback by their close resemblence to Audubon's Shearwater - indeed boydi was included as a form of Audubon's in the recently published 'Albatrosses, Petrels & Shearwaters of the World' by Onley and Schofield (2007). Boyd's appears to share the 'long-tailed' appearance of Audubon's with similarly dark longest undertail coverts. Very little information appears to exist on actual plumage features separating Audubon's and Boyd's Shearwaters and looking at Vaughan Ashby's images from the Cape Verde Islands, I'm not surprised! The most consistently cited difference appears to be leg color; pink or flesh in Audubon's and notably pale (powder) blue in Boyd's. Difficulties in ascertaining an accurate definition of leg color at sea are well known but even so, I think it may be possible on some well photographed birds. Flesh-pink legs show up well on some images of Audubon's taken off MA. Barolo's has pale blue legs and feet, but is smaller, more compact with largely white undertail coverts, striking white tips to the upperwing coverts forming wing-bars, and often shows white of the face completely surrounding the black beady eye. These features show up so well in Scott Surner's fine images taken of the MA bird on 08/25/07 and it seems unlikely that such well marked birds would be confused with Boyd's.
Having looked at Vaughan Ashby's images, and poured over the images and plates in the recently published 'Petrels Night and Day - The Sound Approach' by Robb & Mullarney (2008), one has to wonder if Boyd's Shearwater is a bird that's been overlooked in the past off coastal MA? If it hasn't, it must surely be listed as species that might occur in future?
I'd be very interested to receive comments from birders who have first-hand field experience of both Boyd's and Audubon's Shearwaters, and to know if they've have any comments on how to separate them.
Best birding,
James
Thanks: I'm extremely grateful to Vaughan Ashby, Director of Birdfinders, for allowing me to post his excellent images of Boyd's Shearwater taken in the Cape Verde Islands in March 2009. You can find out more about that trip by clicking here.
Thanks: I'm extremely grateful to Scott Surner for agreeing to let me post his fine image captures from the incredible 2007 record of Barolo's Shearwater off MA. Scott has his own birding blog which's well worth visiting; surnerbirding.com
Note 1: I've followed the species names adopted by Robb & Mullarney in 'Petrels Night and Day', 2008. The authors indicate that these names will also be used by other authors on this subject in the future.
Note 2: A very interesting discussion on the Identifcation of Boyd's and Audubon's Shearwaters can be found be found here on the excellent oceanwanderers website.
Note 3: More discussion on black and white shearwaters from the ID Frontiers Archives, including reference to one of the Audubon's Shearwaters featured here from 2007.
Boyd's Sheawater Puffinus boydi - Cape Verde Islands, March 2009. Vaughan Ashby. Very similar to Audubon's in overall appearance, but the bluish legs and feet can be made out in this shot.
Audubon's Shearwater Puffinus Ilherminieri - Veatch's Canyon, MA. August 23rd, 2008. Here the outerside of the legs look blackish but the webbing between the toes appears distinctly pink.
Boyd's Sheawater Puffinus boydi - Cape Verde Islands, March 2009. Vaughan Ashby. On views like this, would this bird be seperable from Audubon's?
Barolo's Shearwater Puffinus baroli - North of Veatch's Canyon, MA. August 25th, 2007. Scott Surner. Small, compact, black-and-white shearwater looking strikingly white faced, and in this case, showing striking white wing-bars. Exactly the sort of views and images that one would hope for when stumbling across a 'mega'.
Audubon's Shearwater Puffinus Ilherminieri - Hydrographer Canyon area, MA. August 19th, 2007. This bird had a heavily abraded tail giving it a short-tailed impression. The undersides of the pinkish feet can be seen projecting beyond the tail. 
Audubon's Shearwater Puffinus Ilherminieri - Hydrographer Canyon area, MA. August 19th, 2007. Same bird as above. 
Audubon's Shearwater Puffinus Ilherminieri - Hydrographer Canyon area, MA. August 19th, 2007. Same bird as above with a heavily abraded tail giving it a shorter tailed impression. Although just a digibin shot, the pinkish legs and feet can be seen reasonably well. 
Audubon's Shearwater Puffinus Ilherminieri. Hydrogrpaher Canyon area, August 19th, 2007. Gliding low over the sea looking typically long tailed and long necked when compared to Manx and Barolo's.
Boyd's Sheawater Puffinus boydi - Cape Verde Islands, March 2009. Vaughan Ashby. Apart from the blue-gray legs, very similar to Audubon's though perhaps appearing a little smaller and more petite.
Boyd's Sheawater Puffinus boydi - Cape Verde Islands, March 2009. Vaughan Ashby.
Boyd's Sheawater Puffinus boydi - Cape Verde Islands, March 2009. Vaughan Ashby.
Barolo's Shearwater Puffinus baroli - North of Veatch's Canyon, MA. August 25th, 2007. Another amazing shot by Scott Surner showing the white upperwing bars and large expanse of white on the underwing. 
Barolo's Shearwater Puffinus baroli - North of Veatch's Canyon, MA. August 25th, 2007. Scott Surner. Another wonderful image, this time a shot of the oft-quoted slivery panel across the middle of the upperwing. Apparently, this feature can be seen well at range.
