Seagulls are usually gray or white, with black markings on the head or wings. They commonly have harsh wailing or squawking calls. Their bills are long and stout and their feet are webbed. Though their natural diet includes crabs and small fish, they are known to be scavengers and will gladly take human food and are often considered thieves. The main predators of seagulls are sharks, but they would also steer clear from dogs, cats, foxes and other larger animals.