This is the most numerous breeding seabird on the cliffs of Saint Paul Island. The northern counterpart to the Common Murre, Thick-billed Murres can be identified by their black upperparts (brown in Common), white stripe down the upper mandible, shorter and thicker based bill, and pointed upper margin to the white breast. In general Thick-billed Murres breed in long strings of single birds on narrow ledges (Commons prefer to breed on wider ledges, often in tight bunches). Saint Paul provides a unique opportunity to study large numbers of both species in close association. Thick-billed (and Common) Murres are largely resident around the Pribilofs, moving out to the continental shelf break (40 miles west of Saint Paul) in winter. Murres are capable of truly amazing dive depths, with individuals recorded more than 300 feet down, in search of small fish, shrimp or Euphasids.