Finders-in-the-Field: Probable Desertas Petrel off Scilly, 23 August 2019
Scott Reid and Bob Flood
Scott Reid: Heading in to the final weekend of the August 2019 Scilly Birder Special Pelagics season, it was safe to say that the pelagics had already been another resounding success. The general absence of large shearwaters in the Southwest Approaches this summer has been well documented from British and Irish headlands and pelagics alike. Scilly enjoyed a flurry of Cory’s Shearwaters in July and nothing more than the occasional Great Shearwater in August. Wilson’s Storm-petrel, however, offered themselves up in magical fashion for dozens of thrilled pelagic-goers, peaking at 10+ on the 15 August. As well as the stars of the show, the pelagics logged record numbers of European Storm-petrel, thousands of Manx Shearwater, a steady passage of Sooty Shearwater, all four skuas including a beautiful pristine juvenile blonde Long-tailed, Sabine’s Gull, Grey Phalarope, Atlantic Bluefin Tuna, and hundreds of Common Dolphin, adding up to an outstanding support cast.
Up to that point, what should have been the pelagic bird of the year was a Fea’s-type petrel on the evening of Monday 5; Bob was stood in the raised cabin and picked it up racing across our wake as we steamed back towards St Mary’s. Conditions were rough and wet, pelagic-goers were largely huddled together near the cabin, the light was dim, and in the chaos that ensued just one other person managed to get on the bird as it zipped away from us into the gloom! A painful reminder of the challenges of seabirding and a difficult pill to swallow at the time, but I felt assured that my chance would come again one year or another.
I saw for the first time a good number of Desertas Petrel last August during a trip to Madeira but, as I’m sure is the case for any avid British seabirder, the opportunity to see a Fea’s-type petrel in our own waters is an exhilarating prospect.
On Friday 23 aboard MV Sapphire with skipper cum seabirder Joe Pender, we headed out to the west of the islands, toward Pol Bank, a productive reef nine miles southwest of St. Mary’s Quay, with our usual optimism and a boat full of 30+ fresh-faced Friday pelagic hopefuls. The challenging big seas and strong winds of the past two weeks had subsided, a light breeze had swung to the east, and the August sun was baking down. Such conditions rarely make for a productive evening, but the previous day’s reports of a Fea’s-type petrel off Bardsey Island and another, a possible Zino’s Petrel, off Ireland had many on board speculating whether we would also get in on the Pterodroma action. In his public-address welcome, Bob jested about seeing a Fea’s Petrel.
We passed the north end of St. Agnes and I headed to the back of the boat to start throwing bread overboard, something we do on every trip to encourage a following of gulls out to sea in the hope that the increased activity will pull in skuas, large shearwaters or other seabirds. As we rounded the island Annet and cut south past the Western Rocks, it soon became evident that there was in fact plenty of action at sea. A Grey Phalarope flew alongside us off the port side and a pale-morph Arctic Skua terrorised our gulls. A small group of Bluefin Tuna passed the bow and Manx Shearwaters began to appear from all directions. Also now dragging a bag of rotting mackerel off the stern, our wake was alive with birds.
Steaming south and with the Western Rocks still in full view a mile behind us, I saw what I thought to be another Manx Shearwater approaching our wake from the right, low to the water about 100 m or so off the back. As it arrived over the wake, it cut back on itself, performing a figure-eight style turn and looped up around 10ft above the water. The unusual and distinctive behaviour drew my attention, and prompted me to drop the bread and lift my binoculars. As I got on to the bird, it half-banked diagonally away to the right, revealing that mesmerising pattern of pure white body against blackish underwings, grey hood and short, deep black bill! The adrenaline hit and sheer panic kicked in as I managed to blurt out a shout of ‘FEA’S PETREL!! THERE’S A FEA’S PETREL!! MIDDLE OF THE WAKE!! FEA’S PETREL!!’.
I could hear an almighty scramble taking place behind me but I couldn’t take my eyes off the bird. That moment I’d been playing out in my mind for so many years was finally happening! With my camera back by the wheelhouse and behind a wall of impenetrable birders, I knew all that I could do was watch, admire and enjoy the moment – my first Pterodroma in British waters! To everyone’s delight it made its way up the wake, coming close to the boat. Then in the blink of an eye it banked and turned, weaving a path toward the Western Isles, never looking back. After about a minute it was lost to view close to the Western Isles and the celebratory cheers and congratulatory handshakes commenced.
The atmosphere buzzed for the remainder of the evening, but whilst those on board enjoyed a spread of other seabirds, I mostly gazed to the horizon replaying the most electric minute of seabirding that I have ever experienced.
Bob Flood: The initial field impression registered a noticeably robust build and largely dark underwing-coverts. Size and structure ruled out Zino’s Petrel permitting Scott to call ‘Fea’s Petrel’. Of course, the hoary old question for the sightings that eliminate Zino’s Petrel is, ‘was the bird a Cape Verde Fea’s Petrel Pterodroma feae or a Desertas Fea’s Petrel P. deserta?’ The conventional wisdom assumes that field separation of this cryptic species pair is not possible, an issue muddied by some generalisations in the otherwise exceptional article on the subject by Hadoram Shirihai and co-workers (Birding World 23: 239-275).
Our CSI (Cryptic-species science investigation) approach has shown conventional wisdom wrong in a number of cases; e.g. there is no evidence that dark-rumped Leach’s frequent the Atlantic (cf. Swinhoe’s; Storm-petrels & Bulwer’s Petrel guide R. L. Flood & E. A. Fisher), Barolo Shearwater does occur with a ‘dark face’ and dark under primaries and Boyd’s Shearwater with a ‘white face’ and extensive white in the undertail-coverts (Dutch Birding 41: 215–237, R. L. Flood & R van der Vliet), we can go further in the separation of Cory’s Shearwater and Scopoli’s Shearwater than the currently taken as given criteria (to come in our Shearwaters, Jouanin’s & White-chinned Petrel guide, R. L. Flood & E. A. Fisher, due out later this year), and so on. All of these studies involved extensive observational research at sea (months, probably years at sea), weeks studying specimens in museums, and numerous stayover visits to breeding colonies. Our CSI approach has yielded several pleasing results including our analysis of a bird photographed off Hatteras that secured acceptance by the American Birding Association as the first Zino’s for the USA. For me, Cape Verde Fea’s vs Desertas Fea’s is another job for CSI forensics and the job is on my list of things to do once the shearwaters guide is published. I look forward to this and it will be a very exciting challenge.
I have a start point. In our Pterodroma Petrels guide (R. L. Flood & E. A. Fisher) we included several photos of Desertas Petrel off Madeira with a ginormous can opener for a bill, a large bulbous head, a bull-necked appearance, and a large chunky body, with the most extreme cases, presumably males, looking brutish (see pages 154 to 157 of the guide). I have not seen such a brutish creature in the 100s of Cape Verde Petrels that I have seen in the Cape Verde Islands. I have seen and agree with Hadoram that there are stockier looking individuals in the Cape Verde Islands, and this requires more research, but they are not brutish.
Further, I have now been on the waters off Madeira on over 40 days over 10 years, many of them with friends Catarina Fagundes and Hugo Romano who operate the excellent Madeira Wind Birds pelagic trips, and have seen many Desertas Petrels. The great majority of those birds show a pale/whitish crescent in the under outer-wing along the base of the greater primary coverts, which is also shown by the Friday 23 bird. Hadoram’s statistics state that about 70% of Desertas Fea’s exhibit this feature (14% of Cape Verde Fea’s), but field experience suggests more than that. In our Pterodroma Petrels guide on page 207, we translated Hadoram’s study of underwing patterns of the feae-complex into a scorecard q.v. (reproduced below, numbers in boxes are the %ge of birds that exhibited the shown pattern in primary coverts and secondary coverts).
The pending study will address the question of whether some combination of characteristics might be enough to clinch ID of some Fea’s-types seen off Britain. A brute with a pale/whitish crescent in the under primary greater coverts – characteristic of Desertas Fea’s – seems a good start point.
In sum, there is nothing flippant about our stating that the Friday 23 bird was a probable Desertas Petrel. For me, everything about that bird resonates with my extensive field experience and studies of Desertas Fea’s and Cape Verde Fea’s, i.e. the feel/jizz and the detail.
Right, enough of this distraction, back to the Shearwater guide…
Scott Reid and Bob Flood
28 August 2019
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