Sympatric and Allopatric Breeding of Atlantic Yellow-legged Gulls
Southern atlantisbred sympatrically (Grande & Palacios, 2002) in June 2001 with Lesser Black-backed Gulls Larus fuscus graellsii on Alegranza and Montaña Islands, just north of Lanzarote, in the Canaries. Five to six pairs of graellsii nested within a colony of atlantis with no evidence of interbreeding, mixed pairs, interspecific courtship, or hybrids; at least one pair of graellsii apparently fledged young.
The position with Iberian atlantis and cantabricans is not so clear. Paterson (1997) reports frequent hybridisation (about 40 cases per year in the early 1990s) of this form of atlantis with graellsii on the Atlantic coasts of Portugal and northern Spain. Hybrids may occur, one possible hybrid adult is shown from Tanger, Morocco .
In the Atlantic/Mediterranean intersection area in Andalucia, Spain, Iberian atlantis occupy different habitat to Mediterranean michahellis (Rossiter, 2002). The atlantis breed on sea cliffs and the michahellis on marismas and lagoons. The colonies in such habitats are exclusively of one form.
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