A new paper by Olof Jönsson published in Birding World describes the breeding of a new bird species for Morocco and Africa: the Great Black-backed Gull (Larus marinus). And equally important for birders, the paper also discusses the status of Cape Gull (Larus dominicanus vetula) at Khnifiss Lagoon and the Western Palearctic. The latter species was discovered at the lagoon earlier and was considered to breed there.
Here is the summary:
Since the discovery of four displaying Cape Gulls (Larus dominicanus vetula) in Khnifiss Lagoon, Morocco in February 2008, the site has become a popular destination for Western Palearctic birders. The Cape Gulls were apparently residents and the number increased to a maximum of ten adults in April and May 2009, and breeding took place the same year. In May 2010, after analysing photographs of ‘Cape Gulls’ from the site in April 2010, it was discovered that all the photographed birds from that month were, in fact, Great Black-backed Gulls (L. marinus). An analysis of as many photographs as could be found from the area revealed that only two [ad 20 May 2009, 2 ads 7 Jul 2010], probably three [2 presumed ads 23 Apr 2009], of the records supported by pictures showed Cape Gulls. All the rest either showed Great Black-backed Gulls or were too poor in quality to show which species they portrayed, while one picture [29 Apr 2010] showed an adult apparent hybrid, probably a Yellow-legged [L. michahellis] x Great Black-backed or Yellow-legged x Cape Gull. Up to six adult Great Black-backed Gulls were at Khnifiss Lagoon during at least February to July 2010, with one pair apparently nesting, while a pair of Cape Gulls were also apparently on territory on the island in Khnifiss Lagoon on at least 7th July. In January 2011, birders aware of the situation made thorough searches in the lagoon by boat and found ten Great Black-backed Gulls, but no Cape Gulls.
Jönsson, O. 2011. Great Black-backed Gulls breeding at Khniffis Lagoon, Morocco and the status of Cape Gull in the Western Palearctic. Birding World 24: 68-76.
See below 3 updates (comments, hybridisation and more photos of apparent hybrids).
Birders’ comments (update 1)
Norman van Swelm wrote the following in Frontiers of Identification on 11 March 2011 (reposted on birdforum):
According to Olof Jonsson in Birding World 24(2): 68-76 just out. In 2009, a presumably full Kelp pair and a mixed pair Kelp Gull L. dominicanus x Atlantic Gull L. atlantis were found nesting after 5-10 Kelp Gulls were seen displaying on the Atlantic coast of southern Morocco.
In 2010 a pair was found breeding at the same spot but surprisingly turned out to be Great Black-backed Gulls L. marinus instead of Kelp Gulls!
The features pro GBBG in the pair are given as: all white tip to P10 and subterminal white spot on P9; the eye looked pale; a red orbital ring; the feet looked pink; tips of inner primaries with rather narrow white tips.
According to the author a true Kelp Gull should show: a mirror only on P10; evenly broad white trailing edge along the inner five primaries; always dark eyes (quoting Jiguet et al); yellowish-orange orbital ring during breeding and pale yellow outside the breeding season; olive-coloured legs.
The pale colour of the eye is presented as a crucial element in deciding the birds are GBBG’s. Apparently it has escaped this author and others before him that some Kelp populations have pale eyes too! Have a look for instance at the various plates in ‘Gulls of the Americas’ showing pictures of L. d. dominicanus taken in Chile and Argentina and L. d. austrinus from Georgia all with very pale eyes!
Plate 10 in the BW article shows a young bird, said to be a first winter GBBG (photo taken on 18th November). This bird shows very worn tertials and a pattern on the fresh mantle feathers that is quite unusual for birds of that age.
All in all a very interesting article but I doubt the last word has been said on the Moroccan gulls. Future visitors to the breeding island are advised to measure the eggs and to collect feathers for DNA analyses.
Lee G. R. Evans responded in the same forum by this:
I have just returned from Khnifiss Lagoon in southern Morocco where these large black-backed gulls breed and studied these birds again after initially believing all 10 were Cape (African Kelp) Gulls. Two individuals are fairly typical adult Cape Gulls but the other six adults I recorded were pale-eyed, pinkish or pinkish-grey-legged individuals resembling Great Black-backed Gull. They all appeared to be paired up and were displaying and were present at the island breeding colony shared with Atlantic Yellow-legged Gulls.
This is a unique situation and a very confusing one – Great Black-backed Gull generally breed to the north of Scandinavia in the extreme north but isolated populations such as this have also now been discovered in southern Spain. The birds at Khnifiss Lagoon are clearly resident and breeding and almost certainly intergrading – some individuals share mixed characters.
Thanks to Richard Klim for providing the summary and for mentioning the above discussion in birdforum.
Hybridisation (update 2)
Vincent Legrand posted in Netfugl a photograph of a Cape Gull taken at Khnifiss Lagoon on 19 March 2011 with the following comment:
Found just before dusk after 2 full days of intensive research. At least, we saw no less than 13 Great Black-backed Gull on the same spot (2nd winter 2, 3th winter 1, subadult/adult 10 together with a strange looking 3th/4th winter GBBGull, a Cape Gull-like at more than 30 meters, see the 2 photos of ‘Apparent hybrid gull 1′ below). The Cape Gulls of the picture are at 980 m from us. Look on the broad trailing edge (best key on the ground to me), the greenish legs and overall appearance of GBBG. They have a small mirror on P10 and a full black on P9 visible only in open wing. Close to GBBG in size but however they look slightly smaller but bigger than Yellow-legged Gulls. Any comments are welcome.
As a response to Vincent Legrand’s pictures, Martin Garner posted the following in his site, Birding Frontiers:
Cape Gull hybrid? Khniffis Lagoon conundrum continues.
On the Atlantic coast of Morocco the conundrum of the large and dark backed gulls continues to play out. Both Cape Gulls and Great Black-backed Gulls have been seen, what seems uncertain is how many of each species have occurred at different times. Enter the other element of small pioneering gull colonies: the high incidence of hybridization. You can begin to imagine the problems!
Atlantic Yellow-legged Gulls also occur in the area. So the photos of the bird (‘Apparent hybrid gull 1′ below) taken on 19 March 2011 by Vincent Legrand are intriguing. They are stunning photos and at first glance my best guess would be something with a GBBG type head and bill (watered down) that had a Yellow-legged Gull as its other parent. However as Vincent has pointed out, the white trailing edge to the primaries is particularly wide. A feature of Cape Gull. So hypothetically, an adult Yellow-legged Gull X Cape Gull hybrid?! And the inevitable scary question- what if the Great Black-backed and Cape Gulls hybridise?
More apparent hybrid gulls (update 3)
Enjoy your visit to the lagoon and enjoy gulling!