The Blue Petrel is a unique, prion-like petrel of the Southern Ocean. It resembles the prions (Pachyptila) in its bluish-gray upperparts, black "M" pattern above, and stocky, short-tailed structure. It differs from prions in having a white terminal band to the tail, a black hood, and a relatively slender bill. It breeds on Diego Ramírez Island in Cape Horn and South Georgia Island as well as islands elsewhere in the subantarctic. Non-breeders, perhaps mostly young birds, wander north to waters off Peru and northern Argentina, as well as elsewhere through the Southern Ocean. Blue Petrels often feed in flocks, and also nest colonially in burrows excavated in soft soil with grass cover.