Tuesday, February 8, 2011

THE GULLS OF PUGET SOUND

Gulls can be best viewed where we concentrate them, anywhere from fast-food restaurants (French fries are a favorite) to waterfront parks (white bread a staple of the menu) to a meat- or fish-processing plant where they relish the offal, awful as it is. For the most part, the large gulls dominate these assemblages, although if there are few of them, smaller species may be in attendance. The smallest species, Mew and Bonaparte’s Gulls, have different feeding habits and are not part of these spectacles.

As pointed out in a previous blog, the Glaucous-winged is the most common and certainly most ubiquitous gull in Puget Sound. It and the much smaller Mew Gull are the ones you see everywhere throughout the winter. During spring and fall migration, large numbers of Bonaparte’s Gulls appear, and during fall migration there are even larger numbers of California and Heermann’s Gulls.

In addition to these five species, several others are seen in much smaller numbers. Thayer’s and Western Gulls are uncommon during winter, Herring and Ring-billed Gulls even less common. After these nine regularly occurring species, any other species is much rarer. This discussion will concern itself with adult plumages; the immature plumages are usually quite different.

Heermann’s Gulls (Larus heermanni) are medium-sized and stand out by their entirely gray body and black tail; the bill is red, the legs black. In breeding season, the head is white, but we don’t see it in that plumage, as it is a fall visitor from breeding colonies in Baja California. It is more common in the northern part of Puget Sound, mostly in September and October.

Bonaparte’s Gulls (Larus philadelphia), usually seen in migration but remaining for the winter in small numbers, are easily distinguished by their small size, black bill and red legs, and extensively white wingtips. In breeding plumage, they have a black head. They tend to be in flocks, sometimes large ones, and they often feed along convergence lines, or “tide rips.”

All the other gulls have gray mantles, yellow bills, and white heads, bodies, and tails in breeding plumage. Mew Gulls (Larus canus) are the smallest of these, not much larger than Bonaparte’s. Adults have thin, almost pigeonlike, yellow bills and yellow legs. The eyes are brown, the mantle (back and upper surfaces of wings) medium gray. In nonbreeding plumage, the head and neck are strongly marked with gray. The extreme wingtips are black, with large white spots that furnish a characteristic field mark. Like Bonaparte’s, this species is most commonly seen feeding along convergence lines but is common and widespread throughout the region in winter.

The next larger is Ring-billed (Larus delawarensis), with mantle paler gray and contrasty black wingtips. The white tip spots are smaller than in Mew. The bill is yellow with a black ring, the legs yellow, and the iris yellow. This freshwater species is only occasionally seen on Puget Sound but is noteworthy for its very contrasty markings.

A bit larger, the California Gull (Larus californicus) is patterned about like the Ring-billed but has a darker gray mantle, like the Mew, and brown eyes. Note both mantle color and eye color alternate with progression from Mew to Ring-billed to California. The yellow bill features a black spot in front of the red spot characteristic of all the larger species.


The rest of the regularly occurring gulls, larger yet, have yellow bills with a red spot on the lower mandible and pink feet. Thayer’s (Larus thayeri) and Herring (Larus argentatus) are very similar, both with pale gray mantles and less black at the wingtips than either California or Ring-billed. Herring always has a yellow eye, Thayer’s usually a brown eye, but the eye is pale in some individuals. Thayer’s is slightly smaller, with a distinctly smaller bill and more rounded head shape. The wingtips of Herring are blackish above and below, while in Thayer’s, there is not only less black but it shows up scarcely at all from below. So wingtips black above and pale below are characteristic of Thayer’s.


Finally, the two largest species, Glaucous-winged (Larus glaucescens) and Western (Larus occidentalis), differ primarily in mantle and wingtip color. In Glaucous-winged, the mantle and wingtips are gray and darker gray, in Western dark gray and black, respectively. Very different-looking birds, they unfortunately (for the birdwatcher) hybridize freely in the Puget Sound area, and the hybrids come in all shades of gray. These have been called “Olympic gulls,” and they complicate field identification. The wings are always more uniform than they are in Herring and Thayer’s, in which the light gray mantle and black wingtips contrast strongly.

Western Gulls have slightly larger bills than Glaucous-winged and are more likely to have yellowish eyes. The skin around their eyes is yellow, the same in Glaucous-winged is pink. But again, the hybrids complicate the issue. Western is much less common in Puget Sound, but there are pure Westerns along with the hybrids. A pure Western usually retains a white head throughout the winter and doesn’t acquire a black smudge on the red bill spot as does Glaucous-winged.

See the Slater Museum’s gull web page (http://www.pugetsound.edu/academics/academic-resources/slater-museum/biodiversity-resources/birds/identification-of-pacific-nort/) for more images and further information on identification.

Dennis Paulson

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