Fairly common in Gulfstream in summer, scarce in winter. Thick-necked and muscular. ID: Variable in head pattern, extent of white on neck and rump, and back color (probably multiple species but we have poor knowledge of breeding grounds - note head pattern). Usually show strong contrast in underwing, and also between white underparts, nape and rump which contrast with dark cap and upperparts. 'M' on upperparts subtle. Arcs high in bad weather. Sits in small groups, often with storm-petrels. Often sits over food with wings raised.