The common loon or great northern diver (Gavia immer) is a large member of the loon, or diver, family of birds. Common loons eat a variety of animal prey including fish, crustaceans, insect larvae, molluscs, and occasionally aquatic plant life. Adults have a plumage that includes a broad black head and neck with a greenish, purplish, or bluish sheen, black.. The wailing call of the loon is widely used in film and television to evoke wilderness and suspense, very mysterious bird.