Saturday, 13 October 2012

Lesser black-backed Gull or hybrid????

In the end of Sepetember a fellow birder, Pedro Ramalho spotted this pale gull at Peniche, with confusing traits that seem to be shared by both  Larus michahellis and Larus fuscus graellsii.
At first glance nothing wrong for a large male graellsii with heavy winter streaking and head structure, but grey tones of upperparts seem to fit michahellis better, and also orange gonys reaching the upper mandibule.

In fact an hybrid could not be discarded, most probably Larus michahellis x Larus fuscus graellsii. Lesser black-backed Gull was recorded for the first time breeding at Berlengas Islands offshore Peniche in 1977, when a mixed pair with YLG was detected, since then monospecific pairs have also breed, but hybridisation continues to take place, last known data from 1998 (L. Morais), 6 monospecific pairs and 17 mixed in Aves de Portugal 2010.
Some dark on primary coverts, so not probably a full adult, and primary pattern typical off Larus michahellis "lusitanius", with black spot on P4, but not excluding graellsii pattern, which could show black through P3 (Olsen 2003).
Any more ideas......????

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