Glaucous-winged Gull, at sea off Newport, Oregon on 6 March 2010 by Greg Gillson.
In the 1953 book, Birds of Washington State, Jewett, Taylor, Shaw, and Aldrich described the southern edge of the breeding range of Glaucous-winged Gull as Destruction Island, Washington, nearly due west of Mt. Olympus on the Olympic Peninsula. Likewise, that island about 4 miles offshore was the northern edge of the breeding range of the much darker Western Gull.
Today the situation is much different--for the Glaucous-winged Gull, anyway. This pale gray gull, with upper wingtips concolorous (in all plumages) with the rest of the upper wing and back, now breeds south to the central Oregon coast.
The range expansion created a new population dynamic. In the 200 miles where the two ranges now overlap, Glaucous-winged and Western Gulls hybridize extensively. The fertile crosses and back-crosses span the entire spectrum from looking quite pale like Glaucous-winged Gull to very dark like Western Gulls. The hybrid swarm is often referred to by birders in the Pacific NW as "Olympic Gulls." In fact, many birders along the central Washington coast do not try to differentiate them, even when surveying seabirds.
In winter, Glaucous-winged and hybrid gulls are common along the coastline south to San Francisco or farther, in the Puget Sound area, and inland in the larger towns west of the Cascades, and increasingly as vagrants across North America. In contrast, "pure-looking" Western Gulls are rare away from the immediate coast.
As with most larger gulls, they are omnivorous, eating anything they can swallow. They are common in garbage dumps and parking lots of fast-food establishments.