Mew Gulls are one of the smallest of the "white-headed" gulls and are a common sight along the North American Pacific coasts. They are known as Common Gulls in Eurasia.
Adults are medium-sized to small gulls with an unmarked yellow bill, white head and underparts, medium gray upperparts, black wingtips with white spots, and yellow legs. Juveniles have a dirty, grayish brown head, back, and chest. Their back feathers with light tips, giving a scaly appearance. The underparts light brownish gray, barred on the flanks. The tail dark brown, with slightly paler base. Their wingtips are blackish. They posses a black bill, dark eyes, and pinkish legs. On their first winter, the gulls are like juveniles, but the head and belly are paler. During their first summer, they have a gray back. The wing coverts worn and white. They have a whitish head. The wingtips worn and pale. On their second winter, they have a mostly gray back with a few brown feathers. The head and neck are washed with grayish brown. The tail is white with an irregular black band near the tip. The feathers of wingtips black or blackish, with only small white spots.
Adults have a length of 16.1-18.1 inches (41-46 centimeters), a weight of 12.7-21.2 ounces (360-600 grams), and a wingspan of 42.1-44.9 inches (107-114 centimeters).
Mew Gulls occurr in northwestern North America, East Asia, and Europe. They breed in tundras, marshy areas, ponds, lakes, rivers, streams, islands, and coastal cliffs. They winters in nearshore waters and coasts, river estuaries, beaches, mudflats, harbors, and sewage outfalls and treatment ponds.
Mew Gulls eat fish, insects, earthworms, grain, garbage, marine invertebrates.
The nest is placed on the ground or a tree. It is a shallow cup of vegetation, made of dry grass, twigs, moss, lichens, small roots, or bark, frequently with a stone placed centrally in it. They will have one to five eggs in each clutch, the eggs being light olive with variable amount of dark brown speckles. At hatching, the hatchlings are semiprecocial and may leave nest cup in several days. They are covered in cryptically colored down.
The Mew Gull flutters over water with its head down and legs dangling to pick up bits of food from water surface. It sometimes paddles against the current, picking up food as it floats past. They occasionally dives into water for fish.
They call a high, sharp squeak, that is more abrupt than whining of most other gulls.
Mew Gulls are not threatened in any part of its range.
- The Mew Gull has an extensive breeding range, with three distinct forms that are sometimes considered different species. The European form, known as the "Common Gull" has less white in the wingtips than the American form, or "Short-billed Gull," and its first-year plumage is much paler. The eastern Asian form known as "Kamchatka Gull" is larger, with a larger bill, and pale yellow eyes.
- The Mew Gull is the only "white-headed" gull that regularly uses trees for nesting.
- The oldest recorded Mew Gull was at least 20 years and 8 months old when it was found in British Columbia in 2007. It had been banded in Alaska in 1986.
- Mew Gulls are called Gaviota Cana (in Spanish) and Goéland cendré (in French).