This is the third and final article in a series on the identification of the various plumages of the common gulls of northern California. Part 1 defined basic terms, and described molt sequence and the various plumages of ring-billed, California and herring gulls. Part 2 described the plumages of the western and glaucous-winged gulls and their hybrids. This article summarizes the identification of the other gulls which are relatively common in the area: Bonaparte's, Mew, Heermann's and Thayer's gulls. (Editor's note: If you missed the first two parts of this series, they are available in the November 2000 Newsletter).

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.

A common migrant along the coast, the Bonaparte's gull is a rare to uncommon migrant in the interior of the state. This small gull has a delicate appearance and flies with rapid wingbeats. They have small pointed black bills which may have a reddish base. Like most small gulls, Bonaparte's gulls take only two years to obtain their adult plumage.

Bonaparte's gull - juvenile. The juvenile plumage is very similar to the 1st winter plumage, except the back, scapulars and sides of the breast are brown instead of gray, and the upper surface of the outer wings have more black in the feathers.

Bonaparte's gull - 1st year. The 1st winter plumage has a pale gray back, scapulars and sides of the breast, and a black trailing edge with a narrow white border on the wings. There is also a dark brown diagonal band on the upper surface of the wing. The tail has a narrow black subterminal band. A blackish ear spot is prominent. The leg color is a pale flesh. 1st summer birds have partial to complete hoods, and the dark markings in the wings are faded.

Bonaparte's gull - adult. The adult plumage has a pale gray back, secondaries and inner primaries with a long wedge of white on the outer wing. The black trailing edge is confined to the primaries and is visible from above and below. The tail is all white. The wintering adult has a white head with a small black crescent in front of the eye and a black ear spot. The legs are usually pink in color. Breeding adults are similar to wintering adults except they have all black heads with white crescents above and below the eyes, and bright red legs. They occasionally show a variable pink flush on the underparts.

Mew gulls are fairly common wintering gulls along the coast. This medium-sized gull is distinctly smaller than a ring-billed gull. They are round headed with large dark eyes. Their wings are roundish in flight due to the last two primaries being approximately the same length compared with other species where the outer primary is longer than the adjacent one. Mew gulls swim with a distinct posture holding the tail and wing tips raised high above the water surface. The bill is narrow at the base and slightly decurved with no prominent gonydeal angle. The small plover-like bill and small size is distinctive in all plumages. They take three years to obtain the adult plumage.

Mew gull - juvenile. Juveniles are similar to 1st winter birds, except they have more brown on the head and back, and are darker brown below.

Mew gull - 1st year. The 1st winter bird has a body which is heavily mottled with gray-brown above and below, showing a variable amount of pure medium-gray on the back. Pale inner primaries contrast with dark brown outer primaries and secondaries. There is no visible bar on the forewing. The tertials have broad buffy tips. The underwing linings are uniform brown. The tail is almost entirely brown contrasting with a pale terminal edge and whitish rump that is heavily barred. The head and belly is heavily mottled with brown, particularly in winter. There is often a dark smudge in front of the eye. The pink-gray bill has a black tip. The legs are pinkish-gray in color. Summer birds are paler than 1st winter birds, but the darker back and scapulars contrast with the paler secondaries and wing coverts.

Mew gull - 2nd year. 2nd winter birds resemble adults but usually they have broken dark subterminal tail bands, more extensive black in the outer primaries and primary coverts, less white tips to the primaries, dark markings on the secondaries and tertials, and grayish bills with dark tips. Compared with ring-billed gulls, the outer primaries form a narrower dark wing tip with a dark brown trailing edge on the inner primaries. The eyes are sometimes pale. The legs are blue-gray to pale flesh.

Mew gull - adult. The medium-gray back is dark like a California gull's, darker than on ring-billed and herring gulls. They have large white mirrors on the black tips of the outer two primaries and white separates the gray and black on the other primaries. This gives the impression of a very white wing tip. There is a broad white trailing edge to the wing. From below the gray shading to the secondaries contrasts with whitish underwing coverts similar to the pattern of California gulls. There is also a broad white tip to the tertials. The head, tail and underparts are white with extensive gray-brown mottling or wash on the head, neck, and sides of the breast during the winter. The head is pure white in the breeding season with a bright yellow bill and red eye ring. The bill is duller and may have dusky color near the tip in winter. The eye color varies from dull yellow to dark amber. The legs are usually greenish-yellow in color.

Most references identify the Heermann's gull as a three-year gull. However, Jon Dunn in "The Advanced Birding Video Series" presents evidence that they actually take four years to obtain the adult plumage. The species is a slender, medium-sized gull similar in size to the ring-billed gull. They have a strong purposeful flight and immatures in flight may be confused with jaegers at a distance. The legs are black in all plumages. Heermann's gulls are a post-breeding visitor along the coast with most present from June to December.

Heermann's gull - juvenile. Juveniles are all dark brown with pale fringes to the back, scapulars and wing coverts giving them a scaly pattern. The primaries, secondaries, under wing and tail feathers are plain blackish-brown.

Heermann's gull - 1st year. The 1st year bird has an overall dark chocolate-brown plumage with no gray coloration in the back, and no contrasting white trailing edge on the wings and tip of the tail. Most of the juvenile wing coverts are retained which contrast with the uniform brown body and upperparts. The flesh-colored bill has a dark tip.

Heermann's gull - 2nd year. 2nd winter birds have a gray wash to the brown upperparts and white tips to the tertials. The underwing and underparts are uniform gray-brown. The body is grayer, slightly darker above and lighter gray below, showing less brown than 1st year birds. The hood is slightly darker than the back of the head. They may have narrow white trailing edges to the wings in flight and narrow white or buffy tail tips. The slate-gray rump contrasts with the darker tail and back. The bill is orange or reddish at the base with a black tip. They usually have thin pale eye crescents.

Heermann's gull - 3rd year. 3rd winter Heermann's gulls are like adults with duskier hoods which have a brownish cast. Their hoods are noticeably darker than the hoods of adults and they show greater contrast with the gray neck and back: the adult's head is lighter than the back of the neck. They have a partial eye ring. The bill is more orange than in the adult. The primaries lack white tips.

Heermann's gull - adult. Adults have dark gray bodies with black tails and primaries. The combination of dark upper and lower surfaces of the wings is unique. They have a white trailing edge to the wing in flight formed by narrow white tips to the secondaries and primaries, except on the three outer primaries which lack white tips. The tail has a white tip. Adults have strong white tertial and scapular crescents. The head is streaked gray-brown with a paler forehead and lores in winter. The chin and throat are white. A partial eyering is present. In breeding plumage they have an all white hood grading into gray on the neck. The black-tipped bill is bright red during the breeding season and dull red in the winter. The legs are blackish.

The Thayer's gull is an uncommon to fairly common winter visitor to the California coast. They are intermediate in appearance between Iceland and herring gulls, and have been regarded as subspecies of each of these two species in the past. Thayer's gulls are slightly smaller than herring gulls. They usually have rounder heads and short, relatively slender bills giving a "gentle" look similar to a mew gull. In all plumages, the dark on the outer primaries is on the outer web of each feather, except at the tip where it extends onto the inner side. This means that the dark is visible mainly from above. From below, only the pale inner portion of the primaries is visible, so that the under wing appears whitish except at the extreme tips where the small area of dark on both sides of each feather is visible. The leg color of all ages of Thayer's gull is pink, often being brighter than in related species. The eye is dark brown in all plumages, although a few adults have a yellow eye that is flecked with brown. Thayer's gulls require four years to mature.

Thayer's gull - juvenile. The juvenile plumage is similar to the 1st winter plumage although it is usually darker, sooty brown. This plumage is rarely seen away from their arctic breeding grounds

Thayer's gull - 1st year. The 1st winter plumage is quite variable in overall color but is typically a uniform buffy brown with a distinctly checkered appearance to the back and wing coverts. The primaries are uniform grayish-brown or chocolate brown, only slightly darker than the back, and never black as in most herring gulls. The primaries have pale buffy fringes. The secondaries and tertials are gray-brown, usually lighter in color than the primaries. The underwing is mostly uniform pale gray-brown shading to whitish on the outer, unmarked primaries. The tail is uniform brown in color which contrasts with mottled tail coverts giving the bird the appearance of having a broad uniform tail band. The head and neck is streaked gray-brown, paler on the face and back of the head. However, they do not typically show the white-headed appearance often seen in 1st winter herring gulls. Many individuals show a dark smudge in front of the eye. The bill is all black for the first year, whereas, herring gull's have pale bases by the 1st winter.

Thayer's gull - 2nd year. 2nd year birds retain the pattern of the wings and tail similar to a 1st year bird, except the dark areas on the outer primaries and tail band are a paler brown, but still darker than the rest of the upperparts. The back and scapulars are gray like a 3rd year Thayer's (slightly darker than a herring gull's), but the tertials and wing coverts are plain pale creamy-brown giving the upperparts a "washed-out" look. The bill has a pink base and dark tip. The overall look recalls that of a 1st winter mew gull.

Thayer's gull - 3rd year. 3rd winter birds look essentially like adults, except the gray on the wings sometimes is faintly washed with brown, and the tail is usually marked with gray in a subterminal band. The pattern of black on the wing tips is often less sharply defined than on an adult, sometimes extending onto the greater primary coverts. The flesh, yellow or greenish-yellow bill usually has a dark tip or subterminal mark or band, often with some reddish near the gonys.

Thayer's gull - adult. The adult is similar to adult herring gulls except it has brown eyes or pale eyes flecked with brown. The eye often appears large and prominent giving the bird a gentle appearance. They have a slightly darker back and wings which show less black on the upper and under surfaces of the wing tips - the black is confined to the outer web of each primary. Mirrors are present on at least the outer four primaries. Compared with a herring gull in flight, the black on the wing tip is much less extensive on the upper surface, often showing a black-and-white lined effect, and the under surface of the outer wing is white with small dark spots on the tips of the outer primaries forming a thin, dark trailing edge. In winter, they have more uniform pale brown head and neck markings as compared to the grayish streaking found on adult herring gulls. The pale yellow or greenish-yellow bill has a red spot near the gonys (the bill on a herring gull does not have a greenish tone). In the breeding plumage, the dark red or purple eye ring is more obvious than during the winter. The legs are dark pink in color, darker than on adult herring gulls.