Heuglin’s Gull Larus fuscus heuglini, ssp. of Lesser Black-backed Gull, is a large, dark-grey, four-year gull, part of the herring-gull complex. As with all large gulls, determination of species, subspecies, and age is complicated by the high degree of variation among individuals. Identification, therefore, in the field requires experience and caution. The description here is of “taimyrensis,” which some authorities consider to be a hybrid between the nominate heuglini and the Vega gull, and which is a common winter resident along the Chinese coast, particularly the southern coast and Taiwan. The darker nominate race is also encountered in winter in southern China. Large, well-proportioned gull, somewhat square-headed and strong-billed. Breeding adult has white head and underparts, grey mantle and wings, a white tertial crescent, black primaries tipped white, and yellow eyes and legs. Grey of mantle darker than Vega and lighter than slaty-backed gull; Vega gulls have flesh-pink legs. In flight, shows all-white tail and a distinct mirror on the 10th primary and a less distinct mirror on the ninth. Bill yellow with red gonys spot and distinct gonys angle. Non-breeding has brown streaks or spots on head, most prominent on nape. Juvenile and first-winter birds are very dark, with scaly, greyish-brown upperparts and brown, faintly streaked or spotted head and underparts; in flight, shows pale window on inner primaries and broad black subterminal bar (white tips to tail feathers form very thin band). Molts median wing coverts earlier than Vega and is darker and less contrasting than juvenile Vega. Bill black; later develops pale base. Second-winter birds are cleaner and lighter, with grey mantle and scapulars; but wings still have brown patterning, and there is still a black subterminal band on tail. Overall darker than Vega. Bill flesh with black tip. Whinnying and nasal ga-ga-ga calls. — Craig Brelsford
Daniel Bengtsson served as chief ornithological consultant for Craig Brelsford’s Photographic Field Guide to the Birds of China, from which this species description is drawn.