As will be discussed below, the systematics of this group remains very complicated, although recent molecular analysis has shed new light on some of outstanding difficulties. I will group them here with Puffinus shearwaters simply because of the English names. Calonectris Genus of Shearwaters Birds of northern subtropical seas. An important difference from the both the Puffinus shearwaters and Procellaria petrels is the strong sexual dimorphism with respect to body size. Bill length x bill height for example can be used to sex birds in the field.
Sexual dimorphism extends to the voice, that of the female having a overall lower-pitch.
On breeding islands, will sing in flight as well as from the ground. It has been suggested that Cory's Shearwaters use echolocation to navigate nesting caves at night. The flight style is strong and at times albatross-like. Even at great distance, Cory's Shearwater can be identified by its deep, lazy, wing beats interspersed with long glides close to the water surface. Feed by 'dipping' and by 'surface-seizing'.