This is the second in a series on the identification of the various plumages of gulls which commonly occur in northern California. Part 1 defined basic terms, and described molt sequence and the various plumages of ring-billed, California and herring gulls. This article covers the western and glaucous-winged gulls and their hybrids. Part 3 will summarize the plumages of the other gulls which are relatively common in the area: Bonaparte's, mew, Heermann's and Thayer's gulls.

The following references are recommended to help with identifying gulls: "Gulls: A Guide to Identification" by P. J. Grant, and "Seabirds: An Identification Guide" by Peter Harrison. The best reference I have found is "The Advanced Birding Video Series with Jon L. Dunn." Video 1 covers 13 species of large gulls and Video 2 details 14 species of smaller gulls.

Although rare inland, the western gull is the most abundant gull along the California coast. It is a large, stocky gull with a blocky head and pot-bellied appearance. They have a short primary tip projection where the primaries do not extent far beyond the tip of the tail on a resting bird: it is decidedly shorter than in herring gulls. Western gulls have relatively small heads for the size of their bodies. The stout bill has a sharp gonydeal angle which gives the bill tip a "globbed" or bulbous appearance in all plumages. All plumages have pink legs. They take four years to obtain an adult plumage.

Western gull - juvenile. Juveniles are similar to juvenile herring gulls and best distinguished by a combination of the following average differences: (1) heavier structure - especially a domed forehead and heavy, bulbous bill, (2) all black bill, (3) darker general coloration with darker, more sooty gray head and underparts, and less intricate pattern in the feathers of the back, scapulars and wing coverts, (4) lack of obviously pale inner primaries, and (5) whitish, dark-barred rump which contrasts with an all-dark tail.

Western gull - 1st year. Many of the differences between juvenile western and herring gulls apply for the 1st winter plumages of these species. The 1st winter western gull has a sooty-brown head, body and wings with much dusky black on the primaries and dark mottling on the white rump. Overall, the bird appears "smudgy." It is most easily confused with 1st winter herring gulls which are paler brown and have a finer pattern. In flight, the 1st winter western gull is distinguished from young herring gulls by the contrast between the dark back and pale rump. They have darker wings than herring gulls which is evident from above and below. Unlike 1st winter herring gulls, they lack a pale panel on the inner primaries, and the secondaries are more distinctly tipped with white giving a distinct white trailing edge to the wing. The black bill acquires a pale base in the 1st summer plumage. The eyes are dark.

Western gull - 2nd year. The 2nd winter plumage has a dark gray back with dark brown wings. The wing and tail pattern is often like 1st year birds but the wing coverts are always plainer, paler gray-brown with whitish fringes, and the tail often has a white base on the sides. Like 1st winter birds, there is no pale panel on the inner primaries, and the secondaries are more distinctly tipped with white giving a prominent white trailing edge to the wing. The head, body and rump are whiter than 1st year birds. The bill has a pale base and black tip. The eyes become yellow.

Western gull - 3rd year. The 3rd winter bird is similar to an adult in winter plumage except the upper wing coverts are washed with brown, the white mirror and white outer primary tips are small or lacking, and the tail is variably marked with brown, usually forming a narrow subterminal band. The head and chest have some dark mottling in the winter. The bill often has a dark tip, subterminal mark or band.

Western gull - adult winter. Adults have dark gray backs, scapulars, upper wing coverts, and secondaries. Although lighter in northern birds than those in southern California, they are still darker backed than California gulls. The primaries and secondaries are white tipped and the outermost primary has one white mirror. No matter how dark gray the back is, there is always contrast with blacker primaries. In flight, the underside of the wing shows a large patch of black on the primaries and a pronounced gray bar on the base of the secondaries which is darker than on California gulls. The head is generally white throughout the year although northern birds may be lightly streaked with brown in the winter. The thick yellow bill has a pale red or orange spot on the gonys. The eye is yellowish-white (southern birds) to dull yellowish-brown (northern birds). The eye ring is yellow to orange.

Western gull - adult summer. The breeding adult is similar to wintering adults except the head is whiter. The small white primary tips can be worn to where they are largely absent. The yellow bill has a bright red spot during the breeding season.

The glaucous-winged gull is a common winter visitor along the northern California coast. Structurely, it is similar to the western gull. It is a large stocky gull with blocky head, relatively small eye and short primary tip projection. The bill is stout but slightly longer than on western gull and has a less bulbous tip. All plumages are similar to the corresponding plumages of the western gull but are much paler. They have pink legs in all plumages. Like the western gull, the glaucous-winged gull is a four-year gull.

Glaucous-winged gull - juvenile. Juveniles are similar to 1st winter birds except they are not as pale, especially on the upper breast and back of the head and neck.

Glaucous-winged gull - 1st year. 1st winter birds are uniform grayish to grayish-brown in color, not heavily patterned above. They often show a faint bar in the secondaries, and have a diffuse gray-brown tail band visible from above. Overall, they show a pale mottling and paler primaries than similarly plumaged western gulls. The wingtips are uniform with the color of the rest of the upperparts. Even in flight they are paler than 1st winter western gulls. The underwings appear uniform and pale. The bill is black, obtaining a pale base in the 1st summer plumage.

Glaucous-winged gull - 2nd year. The 2nd winter plumage has a pale gray back and scapulars. The rest of the body and wings are pale buff to white with little mottling. The white rump and base of the tail contrasts with a pale gray tail band. The bill is mostly dark, as are the eyes.

Glaucous-winged gull - 3rd year. The 3rd winter bird resembles an adult but has a partial gray band on the tail, buff mottling on the head and chest, and extensive amounts of dark color on their bills.

Glaucous-winged gull - adult winter. Adults are similar to adult western gulls but they have paler gray backs, scapulars, upper wing coverts and secondaries, and very pale gray primaries showing varying amounts of slightly darker gray near the tips. The gray of the upperparts is intermediate between the pale gray of herring gulls and the medium gray of California gulls. The wing tips are approximately the same darkness as the back with one white mirror in the outer primary. The undersurface of the wings is white. Winter adults show much gray-brown mottling on the head, neck and chest (more extensive than on western gulls). The eye color varies from pale brown to brown, usually looking dark. The eye ring is purplish in color.

Glaucous-winged gull - adult summer. The adult summer plumage is similar to the adult winter, except the head, neck and chest are white.

Glaucous-winged gulls freely hybridize with western gulls where their breeding ranges overlap in Washington and British Columbia. They also occasionally hybridize with herring and glaucous gulls in parts of Alaska. Although more commonly encountered on the breeding grounds, hybrids can be encountered in California during the winter. When observing a possible hybrid, concentrate on the following features: (1) the tone of the gray on an adult's upperparts, (2) the paler or darker contrast of the closed wing-tip compared with the rest of the upperparts - this can be important in distinguishing pure western and glaucous-winged gulls from their hybrids, (3) the degree of contrast of any darkness on the tail with the rest of the upperparts, (4) the bill pattern of 1st year gulls, (5) the bill, head structure and body size which is important for telling Thayer's gulls from hybrids which can show Thayer's gull-like plumage patterns, and (6) the colors of an adult gull's eye and eye ring.

The glaucous-winged x western gull hybrid can be extremely variable, showing every shade intermediate between the parents. Adult hybrids generally show backs and upper wings which are intermediate between the pale gray of glaucous-winged gulls and the dark gray of western gulls. The primaries are usually darker than the mantle but are not usually black like a pure western gull's - they are usually dark gray instead. The underside of the primaries of a hybrid are always paler than they are on a western gull. In addition, since wintering adult western gulls do not usually show extensive streaking on the head, an adult "western" gull with an extensive grayish or brownish wash on the head is probably a hybrid. An immature hybrid is also intermediate in characteristics between those of western and glaucous-winged gulls of the same age.