We just heard that the probable Atlantic Petrel off Cornwall was a dark bird, but don’t know this first hand? Of the many thousands of Atlantics I have seen in the South Atlantic just one was dusky looking, while the rest were typical. Anyway, since Atlantic Petrel is currently topical the following video and note may interest you.
Included here are three sequences of Atlantic Petrel, from relatively distant to very close. Realistically, there are only two potential confusion Pterodromas in the North Atlantic – Trindade Petrel, and the remote chance of a Kermadec Petrel. We will discuss all three species in depth in our forthcoming multimedia guide to ‘Pterodroma Petrels’ (North Atlantic series) including video footage of all three.
A quick note though. I picked up Trindade Petrels on both of my Atlantic Odysseys (2006, 2010) and these are documented with photographs in two Birding World articles (22: 162-166; 23: 305-306). Of particular interest, it took a little time and fairly close views to convince other seabirders present that the first Trindade Petrel in 2010 was not an Atlantic Petrel (of which we had seen thousands). The Trindade was a pale morph, BUT it had incredibly dark underwings, and the limited white on the underwings could only be seen at relatively close range (see photo). The undertail-coverts also looked dark. I thought I had glimpsed white on the underwings when I first picked it up - on the underwing Atlantic also has hard to see pale bases to primaries; but it was its much slimmer structure and less heavy flight jizz that convinced me it was a Trindade. It flew away and lingered some considerable distance off, before (thankfully) steadily working its way back to the ship, finally revealing its identity to all others present and convincing them it was not an Atlantic Petrel.