El Hierro, El Hierro, El Hierro…

7 06 2015

“Is that a seagull?”

– Crístel Reyes

To find a rarity at sea is always something strange, especially when you are not even looking for birds. We know the habitat it’s not the same all over the sea, since the currents and the shape of the depths can make some areas better than others, but, at a glance, the sea looks just like an infinite flat blue plain. You can’t search because you can’t get out of the boat you are in, you don’t depend on your call recognition skills (despite some terns are easier to spot this way)… You just sit and wait.

Maybe this is why you feel especially lucky when a rarity shows up out in the sea. It’s usually not a prize for your id skills but for the number of boring hours you’ve been there, waiting for such an improbable event. As in ringing, from a taxonomic point of view, everywhere there is an interesting common species to look at while waiting for the actual prize: Band-rumped storm-petrel in La Concepción Bank, Cory’s shearwaters at El Hierro, Yelkouans and Balearics in the Mediterranean.

This time the unexpected emerged in the shape of a Red-footed booby, the third to be seen in Spain. We were taking photos of a pod of Atlantic Spotted dolphins feeding with Yellow-finned tuna and Cory’s shearwaters when Crístel said “is that a seagull?” I took a look and immediately said “No, it’s a 3rd summer Gannet”. The bird was flying towards us and I had seen black secondaries. It was not until I got profile views of it that I saw a “Sula face” and a long-tailed bird. Without direct comparison, the size and structure wasn’t particularly striking, what makes me think they can get surprisingly easily overlooked. To be honest, if the sighting had only lasted 30 seconds, I would had not identified it.

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Fortunately, the bird flew over the top predator feast we were photographing and gave close views of both underwing and upperwing patterns. At a glance, I thought it had to be an adult, but the bare parts of the face were not as brightly colored as I had seen in some photos. Moreover, when it flew over us, I noticed some dirty spots in the underwing. Because of embarrassing freaky reasons not worth-mentioning, I had brought my copy of Pyle to a Beaked whale survey in El Hierro. What seemed to be a stupid idea keeping in mind Ryanair’s strict baggage policies, become suddenly useful and, in a village with just a slow wi-fi connection in the local “zumería” (juice bar), I was still able to get some information about the age of the bird.

However, I was not fully satisfied with the information comprised in my otherwise beloved Pyle. According to this author, they can only be aged up to 2nd cycle, since after the 2nd pre-basic, they already show the definite plumage: all white underparts and upperwing coverts, dark eye and brightly colored bare parts. However, 2nd cycle birds are meant to show a dusky tip to the bill. This bird showed an adult pattern in its bare parts, just less colored. The plumage was not adult, but obviously closer to that than what I’d expect for a 2nd summer.

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So I followed the natural sequence of references and checked Howell’s Rare Birds of North America. This time, however, my freakiness had not reached that far and I had to wait until I was back in Barcelona to read what it’s said there. After some minutes admiring Lewington’s wonderful plates, I focused on the aging section. Surprise! Seemingly, some birds can be aged up to 4th cycle, mainly on the basis of remaining brown areas. According to Howell, 3rd cycle birds still can show extensive brown areas in the rump, back, scapulars, inner lesser coverts, axillaries, and underwing secondary coverts. All those areas become white as 3rd pre-basic moult goes on.

El Hierro bird showed all-white upperwing and body and the brown feathers were restricted to lesser under-secondary coverts. It would had fitted therefore with an advanced 3rd cycle if it had not shown an incipient primary moult. The bird is indeed growing P4, what makes me think it’s more likely an early 4th cycle. I’m not sure however if it could had already lost most of the brown areas during the moult of this 3 and a half primaries, what would make it a 3rd cycle. It would be interesting to know (if possible) what is more common: a 3rd cycle with an early stage of primary moult with almost all-white adult plumage or a 4th cycle with remaining brown in the underwing. Comments are welcome!

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Finally, there was still the origin issue to be discussed. The variation in the species is huge, but not all the authors agree to classify it in terms of subspecies. There are 2 morphs: brown and white, and both show 2 “sub-morphs”: white-tailed and dark-tailed. Seemingly, all possibilities can occur everywhere, but in different proportions. The Caribbean and Atlantic population (what would be more likely) belong mainly to the white morph or white-tailed brown morph, whereas 85% of birds from Hawai show a dark tail. As usual, it seems that, in this case, the most-likely explanation seems to be the good one.

It feels like the number of sightings of Red-footed booby in this side of the North Atlantic is increasing, with some recent records in the Iberian Peninsula, France, Canary Islands and especially Cape Verde. Red-footed booby, the next species to start breeding in the WP?

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