The specific glaucescens is Neo-Latin for "glaucous" from the Ancient Greek, glaukos, denoting the grey color of its wings.

[5] It is an exceptionally rare vagrant to the Western Palearctic region, with records from Morocco, the Canary Islands and, most recently, from Ireland in February and March 2016.

During the winter, the head and nape is darker with a varied smudged or mottled pattern, and the bill colour becomes duller, often with dark markings near the tip.

In urban areas it is well known for its tendency to accept food from people and peck open unprotected garbage bags in search of edibles.

In the Puget Sound area, hybrids may outnumber pure birds and backcross with either parent species leading to further identification problems.

Referred to as the Olympic gull,[9] this hybrid is found along the Pacific coast from British Columbia south to California.

[11] In the central part of the hybrid zone, clutch size was larger among pairs with hybrid males, many of which established breeding grounds in more vegetative cover than pure western gull males, which preferred sand habitat resulting in heavier predation.

[12] This hybrid combination may be found along the Pacific coast from Alaska down to southern California, and are highly variable, sometimes resembling Thayer's gull but with a larger bill and inconsistent wing pattern.

Hybrids with Slaty-backed gull are uncommon but have been known to breed on the east coast of the Kamchatka Peninsula and Commander Islands, reaching south to Japan in winter.