On the right is a typical adult Western Gull. You can see that the mantle is much darker gray than that of the Herring Gull on the left. Notice how white and unmarked the head and breast of the Western Gull is. Pure Western Gull adults always show unmarked heads; apparent Western Gulls with winter head streaks are likely hybrids with Glaucous-winged Gulls. Pure Western Gulls are rare inland, away from the immediate coastline. The winter Herring Gull on the left is perhaps less heavily mottled on the head and breast than is typical for early winter, but more typical for March.

The Western Gull in flight is quite unique. Not only are the undersides of the black primary tips dark, but the entire undersides of the flight feathers on the primaries and secondaries are dark gray. This creates a dark trailing edge on the wing which is visible at a great distance, such as birds out over the sea. In contrast, the underwing of Herring Gull is quite white with black under primary tips which mirror the black on the upper wing.

First-winter Western Gulls are big and dark. They are the darkest gull on the beach in winter. The primaries and secondaries (usually not visible on the folded wing, but this bird is holding its wing so that they are exposed) are blackish, as is the tail. The wing coverts have dark brown centers and brown edges. The head, breast, and belly are evenly brown. The bill is large, heavy, and black.

In contrast, the first-winter Herring Gull is much paler, especially about the head. The wing coverts are brown, but have whitish edges and internal bars. By late winter the base of the bill usually becomes pale pinkish.

By the second winter the eye of Herring Gull has turned pale. The longish bill is pink with a black tip. The massive bill of the Western Gull is still mostly black. The backs of both birds have turned adult gray; the gray back of Herring is much paler than the dark gray back on the Western Gull.

Third-winter gulls look quite similar to adults with the following exceptions. The bill usually is not yellow with a red gonys spot. Rather, it is pinkish with black tip. The body plumage is more mottled on the head and breast. The tail is mostly white with a few remnant of a smudged tail band. The wings lack the large white mirrors and apical spots or, if present, they are much smaller than in adult winter plumage.