Dutch Birding volume 30 (2008) no 4

Possible hybrid Glaucous x Great Black-backed Gull at IJmuiden in January-March 2007 and identification

On 6 January and 9 March 2007, a very large pale gull Larus was briefly observed on the beach at IJmuiden, Noord-Holland, the Netherlands. Pale Scandinavian Herring Gulls L argentatus argentatus occur in the Netherlands during winter in small numbers. However, the heavy bill with a striking amount of pink on the base, the completely moulted scapulars, the short primary projection and the lack of clear notches and barring on the tertials made identification as Scandinavian Herring unlikely. The pink bill base and pale appearance suggested influence of Glaucous Gull L hyperboreus. Hybrid Herring x Glaucous Gulls L argentatus x hyperboreus usually show a 'pencil-like' bill, a broader tail-band and more barring on uppertail- and undertail-coverts. The heavy bill with pronounced gonydeal angle made influence of Great Black-backed Gull L marinus more likely. The plumage was intermediate between Glaucous and Great Black-backed. Therefore, it is concluded that the IJmuiden bird was probably a hybrid Glaucous x Great Black-backed Gull L hyperboreus x marinus. As far as known, (presumed) hybrid Glaucous x Great Black-backed Gulls have not been previously recorded in the Netherlands. However, this hybrid is known from Newfoundland, Canada, Greenland, Ireland and Scotland. Unusually pale (eg, 'brown' morph) Great Black-backed occasionally occur and may cause confusion when identifying this type of hybrid.

Leon Edelaar, Sluisvaart 50, 1191 HE Ouderkerk aan de Amstel, Nederland
(l.edelaarchello.nl)