Distinguishing Characteristics

Medium-sized gull (male 60–66 cm long, 1050–1250 g; female 56–62 cm, 800–980 g). Adults have white head, neck, and body, with head and sides of breast often streaked dusky in winter. Only gull with light gray back and wings, black wing-tips with white spots (mirrors), and pink legs in adult stage. Yellow to light orange bill with subterminal red spot. Iris golden (may be lightly flecked with brown) with yellow or orange orbital ring. Has about 7 plumage stages before adulthood (see Appearance).

Species belongs to large complex of Northern Hemisphere gulls, all of which are somewhat similar and may be confused, especially in immature plumages. Taxonomy of group complicated, especially given frequency of hybridization and possible reticulate evolution in Eurasia (Pierotti 1987b, Panov 1989).

Juvenile Herring Gulls mottled dark gray-brown. Can be confused with juveniles of all species listed below. Subsequent preadult plumage stages also difficult to identify; best characters are combination of mantle (back) color and markings on bill. In North America at least 10 species of white-headed gulls can be mistaken for adult Herring Gulls (species listed below with geographic areas of sympatry).

Pacific Basin: Western Gull (Larus occidentalis) similar in size and color of bare parts, has much darker mantle; Glaucous-winged Gull has similar mantle color, slightly larger, with pale gray rather than black wingtips, dark iris with purplish eye-ring (Herring/Glaucous-winged gulls hybridize in se. Alaska; Patten 1980); Mew Gull (L. canus) much smaller, has unmarked yellow bill, yellowish legs. Hybrids between Western and Glaucous-winged gulls can appear quite similar to Herring Gulls; these hybrids often have less black in wingtips. In winter along Pacific Coast and in Canadian prairies, California Gull (L. californicus) smaller, has yellowish green legs and black spot anterior to red spot on bill.

North Atlantic Coast: Great Black-backed Gull much larger with dark mantle and lighter-colored, heavier bill (rare hybrids reported between Herring and Great Black-backed gulls; Pierotti 1987b); Lesser Black-backed Gull has dark mantle, yellow legs (Herring and Lesser Black-backed gulls hybridize in British Isles and Siberian Arctic; Pierotti 1987b, Panov 1989).

Arctic and North Pacific Coast: Thayer’s Gull (L. thayeri) almost indistinguishable, best distinguishing characters dark iris, lack of black on undersurface of wing-tips, white tongues proximal to black tips on primaries. Thayer’s Gull may not be a true species; possibly a form of Herring or Iceland (L. glaucoides) gull.

Winters in North Atlantic: Iceland Gull similar in size and color, has pale, almost white, primaries.

Arctic, North Atlantic, North Pacific, and Great Lakes: Glaucous Gull (L. hyperboreus) much larger (size of Great Black-backed Gull), has white primaries (Herring/Glaucous gulls hybridize in Canadian Arctic; Pierotti 1987b, Spear 1987).

Midwestern U.S., Canada (including Great Lakes), and Atlantic Coast: Ring-billed Gull (L. delawarensis) smaller, has black ring around bill (nearly always) instead of red spot, yellow legs.