The brown seagulls you’re seeing are almost always young birds. Most gull species hatch with brown, mottled feathers and don’t develop the familiar white-and-gray adult plumage for two to four years, depending on the species. That long transition is why beaches and parking lots seem to have two completely different types of “seagulls” standing side by side.
Brown Means Young, Not a Different Species
A first-year Herring Gull, one of the most common large gulls in North America, is mottled brown from head to tail with a black bill. It looks nothing like its parents. The juveniles have tan-and-white checkerboarding on their backs, dark wing tips without the white spots adults show, and a thick dark band across the tail. If you didn’t know better, you’d assume it was an entirely separate bird.
This is true across dozens of gull species. Ring-billed Gulls, Great Black-backed Gulls, Western Gulls, and many others all start life in shades of brown and tan. Smaller species like Bonaparte’s Gull reach adult plumage in about two years. Larger species like the Herring Gull take three to four years, cycling through several intermediate stages where brown gradually gives way to gray and white. Second-year Herring Gulls, for instance, are still mostly brown but start showing gray feathers on the back.
What Makes the Feathers Brown
The brown color comes from pigments called melanins, the same family of molecules that colors human skin and hair. Bird feathers contain two forms: eumelanin, which produces black, brown, and gray shades, and pheomelanin, which creates yellowish to reddish tones. The mottled brown of a juvenile gull comes from a mix of both types deposited in the feather structure as it grows. As the bird matures and replaces its feathers through molting, the new feathers contain different concentrations of these pigments, producing the clean grays and whites of adulthood.
Melanin also makes feathers physically tougher. This matters for young birds still learning to fly and forage, since their feathers take more of a beating than those of experienced adults. The pigment-rich brown feathers are more resistant to wear and bacterial breakdown than pure white ones would be.
How Gulls Transition to Adult Plumage
The shift from brown to adult coloring happens through a series of molts, where old feathers fall out and new ones grow in. It doesn’t happen all at once. In Western Gulls, the first signs of molting out of juvenile plumage appear in late August or September, starting with new feathers on the back and shoulder area. These replacement feathers often have broad pale tips that wear off over time to reveal gray-brown underneath.
The molt follows a predictable sequence. It typically begins with the shorter feathers on the back, then moves to the sides of the chest and face, progressing through the head, neck, and flanks. The last feathers to be replaced are usually on the back of the neck and the largest shoulder feathers. This gradual process is why you’ll see gulls that look patchy, with a mix of brown juvenile feathers and newer gray or white ones. These “in-between” birds can be the hardest to identify, even for experienced birdwatchers.
Each successive molt brings the bird closer to its final look. A third-year Herring Gull has mostly gray wings and a white body but might still show brown flecking on the wings or a smudgy tail band. By the fourth winter, it finally looks like the classic gray-backed, white-bodied gull with yellow bill and pale eyes.
Why Juvenile Brown Coloring Helps
Young gulls benefit from being brown in several ways. The mottled pattern provides camouflage, especially for chicks and fledglings that spend time on the ground near nests, where predators like foxes, hawks, and larger gulls are a real threat. A bright white chick sitting on a rocky shoreline would be far more conspicuous than a brown, speckled one.
The dull coloring also serves a social function. Adult gulls are territorial and can be aggressive toward competitors. Looking visibly different from adults may signal to other gulls that a young bird isn’t a rival for mates or nesting sites, reducing the chance of being attacked. In colonial species where thousands of gulls nest in close quarters, this kind of visual signal matters.
When It’s Not a Young Gull
Occasionally the brown bird you’re looking at isn’t a gull at all. Jaegers and skuas are seabird relatives of gulls that are naturally dark brown or gray-brown as adults. Parasitic Jaegers, which show up along coastlines during migration, come in multiple color forms, including a fully dark morph that could easily be mistaken for an unusual gull. They’re slightly smaller and sleeker than most gulls, with more pointed wings and a more aggressive flight style, often chasing other seabirds to steal their food.
Some adult gulls also retain darker plumage naturally. Heermann’s Gull, common along the Pacific coast, has a gray body and dark wings year-round. Laughing Gulls have dark gray backs. These species can look brownish in certain lighting, but their coloring is consistent across adults rather than a sign of immaturity. If you’re trying to figure out what you’re looking at, the bill color is a helpful clue: juvenile gulls of most large species have dark or black bills, while adults have yellow or red-marked ones.