Bird of the Month: Glaucous-winged Gull
Written by Andy McCormick
Andy McCormick, 2024 Audubon Washington Helen Engle Volunteer of the Year
The omnipresent large, pink-legged gull of the Pacific Northwest, Glaucous-winged Gull breeds in coastal colonies and spends most of its life traversing the world of sea and shore.
“No other large gray-mantled gull shows primaries that are uniform in darkness with the upperparts” (Alderfer). The plumage of a mature Glaucous-winged Gull presents a continuous and uniform medium gray mantle across the back and wings including to the wingtips. This gull has no black in the wingtips in any of its four-year plumages. This is an important and unique difference among the large, white-headed gulls most of which have dark primary feathers which extend beyond the tail when the wing is folded giving those gulls a dark-wingtip look. Glaucous-winged Gulls most closely resemble Iceland Gull (L. glaucoides) which has slightly darker gray wingtips, and Glaucous Gull (L. hyperboreus) which has white wingtips.
A Glaucous-winged Gull reaches adulthood in its fourth year and breeds for the first time then or in its following year. A pair will fashion a nest in a shallow depression lined with a combination of grass, seaweed, or moss in colonies ranging in size from a dozen pair to thousands of pairs. Usually, two or three eggs are deposited, and the parents share incubation time for about four weeks. The chicks hatch downy and leave the nest within days. Then they are nurtured by the parents until they make their first flight at various times between five to eight-weeks after hatching (Kaufman).
Glaucous-winged Gull is placed in the genus Larus from the Greek laros, a ravenous seabird. It is a large genus which contains 24 species of gulls, 17 of which have been recorded in North America. The species name glaucescens, refers to its blueish-gray color. The term glaucus is also an old word for the Glaucous Gull (L. hyperboreus) which, when combined with the suffix -escens, means “somewhat like” comparing the similar appearance of these two gulls (Holloway). These and many other large, white-headed gulls are also similar in size, yellow leg color, and overall structure making identification among birds in this suite of gulls quite challenging.
Glaucous-winged Gull
Scientific Name: Larus glaucescens
Length: 26”
Wingspan: 58”
Weight: 2.2 lbs (1000 g)
AOU Alpha Code: GWGU
NORTH PACIFIC COAST DISTRIBUTION
The Glaucous-winged Gull is generally restricted to the Pacific coast of North America and part of the northeastern coast of Asia. It tends to be a coastal gull with primary breeding colonies located on islands in the Bering Sea from Kamchatka, Russia to southern Alaska. However, there are scattered breeding colonies in coastal Oregon and Washington including on Protection Island in the Salish Sea. Glaucous-winged Gulls populate bays and river mouths, but they are also known to stray inland at times. Others will follow fishing boats and feed pelagically as much as 100 km offshore.
Glaucous-winged Gulls are present in the Pacific Northwest for most of the year, but they stay along the coast during breeding and move into more protected areas such as the Salish Sea in winter. They are short-distance migrants moving with the seasons. As with many migratory bird species, individuals that breed in the most northly latitudes will migrate the farthest south. Many northern Alaskan Glaucous-wings migrate as far south as Mexico in winter.
CONSERVATION AND MANAGEMENT
The North American population of Glaucous-winged Gulls is stable and is estimated to total about 200,000 pairs. However, competing factors have had an impact on some specific nesting colonies. Some local populations have decreased due to suspected factors including a decline in forage fish, predation of colonies by Bald Eagles, and nest raiding by other adult gulls within the breeding colonies. However, increases in Glaucous-winged Gull populations in other locations have been attributed to their propensity to add substitute feeding on human garbage at landfills, a decline in Bald Eagle predation in some areas, and decreased persecution by humans (Hayward and Verbeek).
A WORD ON HYBRIDIZATION
Glaucous-winged Gull is well-known to interbreed with other gulls of its genus. In the southern portion of its breeding range, it hybridizes with Western Gull (L. occidentalis) forming a Glaucous-winged Gull X Western Gull Hybrid. The geographical region along the Washington and Oregon coast covers the middle third of the large hybrid zone. As many as 75% of nesting colonies for these two species in these two states comprise hybrids which are often referred to as “Olympic Gulls” referencing Washington’s Olympic Peninsula (Howell and Dunn). The zone extends north into British Columbia and Haida Gwaii and south to the central California coast with thinning of the hybrid population at both extremes. The vast amount of hybridization including backcrosses with adults of both species creates a wide range of plumage and structural characteristics making identification of large, white-headed gulls in this region very difficult. The hybrids migrate into Puget Sound and other areas of the Salish Sea and the Oregon Coast in winter creating an environment of identifying gulls amidst a “hybrid swarm” (Tweit). North of the hybrid zone Glaucous-winged Gull interbreeds with Herring Gull (L. argentatus) and Glaucous Gull.
Photo credit: Mick Thompson
References available upon request from amccormick@eastsideaudubon.org.