Thursday, June 8, 2017

The Pesky Pterodroma(s) from May 28 & 30, 2017 - by Brian Patteson

Gadfly petrels are some of the most variable looking birds you will encounter.  Look at a couple of dozen Black-capped Petrels and you will quickly see what I am talking about.  Late in the day on May 28 on our pelagic trip from Hatteras we encountered an odd looking bird.  It did not look quite right for a Black-capped Petrel, but it did not really fit well for Bermuda Petrel either.  It stayed in the chum slick long enough for most folks to see it and several photos were obtained. Following photos by Peter Flood
At the time, we tentatively identified it as an odd Black-capped Petrel because seen in direct comparison to Black-capped Petrels it did not seem much smaller.  Bermuda Petrels are generally noticeably smaller than Black-caps, and, while this bird had a hooded appearance beyond the smudging of most darker Black-caps, the tail looked too extensively pale to be a Cahow.  Photo by Peter Flood
The underwing was more like that of a Cahow, but looked even more extensively dark than any Cahows we have observed including dozens of live birds in Bermuda.  Photo by Steve Howell  
The tail was odd.  At a distance it looked mostly white, as in Black-capped Petrel, but inspection of photos revealed a gray tail like a Fea's Petrel.  Photo by Steve Howell 
The bill looked a bit heavy, but probably not too heavy for a big, male Cahow.  We subsequently encountered either the same bird or an identical looking individual about 10 miles away two days later, but the observation was brief and we only have a single photo for comparison.  Photo by Steve Howell  
Again the Fea's-like tail is striking, but the bird had a Cahow-like underwing.  The molt of the bird is not unlike that of a few Cahows that we have seen off Hatteras over the years, and the coloration could be the result of a bleaching by the sunlight like you see in first summer gulls.  But it's not a slam dunk Bermuda Petrel, and the fact that vagrant Cahows and vagrant Fea's have been captured in the Azores makes you wonder what is possible.
-Brian Patteson

 The Cahow Collection - Brian Patteson
all photos by Brian Patteson - 1998 & 2000 slides / 2014 digital
This May 1998 Cahow shows similar molt stage with extensively pale uppertail:
The same individual shows similar molt and gray looking hood:
Final photo of the May 1998 Cahow showing blacker looking hood and molt not unlike the mystery petrel:
Another Cahow from May 2000 with similar molt and pale uppertail:
The same May 2000 bird showing heavy looking bill:
Another Cahow from August 2014 showing a gray looking hood:
The same individual showing brownish upperparts:

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