These shearwaters ain’t foolin’ nobody!

1 09 2015
These GRSH show off their competitive natures and their field marks. The birds in the background look like Wilson's Storm Petrels to me. (Photo: DickDaniels via wikimedia commons)

These GRSH show off their competitive natures and their field marks. The birds in the background look like Wilson’s Storm Petrels to me. (Photo: DickDaniels via wikimedia commons)

As anticipated, pro dead bird identifiers like the readers of this blog recognized the three species in the last post immediately. Bird A is a Greater, Bird B a Sooty, and Bird C a Cory’s Shearwater. Luckily for me, shearwater i.d. tends to be straightforward, and I have a few quick features I look for to make the call at a glance. For the Cory’s, it’s that yellow bill. As the field guides say, that is “distinctive” once you’ve established you’re looking at a shearwater. And the wacky tube nose is a giveaway on that. For the Sooty, the dark breast and belly are the decisive factor here; other shearwaters have white on the underside. The most common shearwater we get on SEANET beaches though is by far the Greater. When looking at a light bellied shearwater with a dark bill, it’s almost always a Greater. But I check every time for what I find the most reliable indicators. GRSH have a dark, smudgy patch on the belly. To the uninitiated, it can look like dirt, or even oil. You all, of course, are initiated, and know that. That is, however, why I chose Bird A particularly. The smudge is variable between individuals, and I found it interesting that it is basically absent in this bird. That did give me pause, so I double-checked with another of my go-t0s for GRSH, the undertail coverts (dark in Bird A). Among the white-bellied shearwaters, the Manx has white undertail coverts, while both the GRSH and Audubon’s have dark. So we should at least entertain Audubon’s when looking at a shearwater that has a white belly and seems to lack any dark smudging.

Though I didn’t provide a picture of the upper side of Bird A in the original post (not that any of you needed it), so I will do so now:

Other side of Bird A. Photo courtesy of L. Ries.

Other side of Bird A. Photo courtesy of L. Ries.

This Bird looks brownish overall on its upper surface. This is definitely a GRSH characteristic; Audubon’s shearwaters are much blacker above. Finally, if you look at the upper surface of the tail, you can see a disheveled pale band in evidence. This is also a GRSH feature; Audubon’s have an all dark rump and tail. The pale tail band also brings up one last species to keep in the back of our mind, though it very rarely turns up; the Black-capped Petrel is not a shearwater at all, but it is a tubenose with a white belly and dark upper side. What sets it apart, however, is a broad, clearly white band on the upper tail, and a sharp black band on the underside of the wing. I am always hoping such rarities will turn up, so I try to keep my mind open to them, and my oddball i.d. skills honed.

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