A young gull's mottled brown plumage acts as a 'not a threat' signal to territorial adults‎

Birds are known for their distinctive plumage that helps them attract mates during the breeding season. For some birds, the path to adulthood is quite linear. One day they are chicks, and a few months later they are fully grown adults with their mature plumage, all set to find and fight for a mate. However, some seabirds linger much longer in the awkward adolescent phase. Species like the American herring gull take several years to develop their adult feathers, a process called delayed plumage maturation.