Atlantic Yellow-legged Gull (atlantis)

(last update: October 12, 2011)

Atlantic YLG adult February

data from: Malling Olsen, K. & Larsson, H. 2004 Gulls of Europe, Asia and North America. London: Christopher Helm.

Moult
Slightly earlier than in michahellis; adult moult P1 mid-May, P7-P8 late July - early Sept, P9-P10 mid-Sept – mid Oct. Head and body from late July, tail and secondaries late July—Sept. Most show winter head and heavy moult in secondaries and tail late Aug – early Sept.
Moult from juvenile to first-winter non-existent, or restricted to parts of mantle and scapulars Sept - Nov. Often juvenile plumage moulted directly into second-winter. Moult into second-winter complete. Reaches P5, coverts and tail by early July (pers. obs. in Azores and Madeira; skins in NHM, UZM).
Moult to third-winter similar to adult, but on average earlier, being finished late July - Aug.

Hybrids
Hybrid pairs of nominate michahellis x Herring Gull reported W France (2) and Great Britain. Hybrid pairs with Lesser Black-backed Gull known W Iberia, W France, Netherlands, Germany and Great Britain. Young known from Netherlands and Germany (Yésou 1994, Garner & Quinn 1997, Ogilvie et all. 2001, Limicola 11: 266, A. Bermejo in litt.).
Probably hybrid second-winter Herring Gull nominate argentatus x Yellow-legged nominate michahellis combined upperparts (with much grey) and dark primaries of michahellis with head-streaks and yellow bill with dark sub-terminal markings (photo 30, Klein & Gruber, 1997).
Putative adult hybrid Yellow-legged Gull nominate michahellis x Caspian Gull nominate cachinnans reported from Poland (two males). These showed darker mantle than nominate cachinnans with broad black markings on P5, and relatively steep forehead and long, deep bill. Legs pale yellow or pale pink. Iris yellow with some brown spotting; measurements closer to Caspian than to Yellow-legged (for details, see Faber et al. 2001). Has paired with Kelp Gull in Mauretania 1997/ 98 (Pineau etal. 2001).
Aberrants A second-winter leucistic from Spain was similar to leucistic Herring; had just moulted inner four primaries Nov. Juvenile with white subterminal markings on primary coverts and primary tips known. Leucistic adult with white P7-P10 and secondaries noticed from Cies Island, Spain (Garcia 1987, A. Bermejo & E. de Juana in litt.).