Black-vented Shearwater
Puffinus opisthomelas
Black-vented shearwater adults are around 30–38 cm in length, have a 76–89 cm wingspan and weigh around 400 g. Males are generally slightly larger than females, though the size difference is minimal. Chicks have grey down feathers, lighter around their throat and breast areas. These down feathers lighten slightly over time. Adults have dark brown heads, and dorsal plumages, with lighter ventral plumage (often white with specks and smudges of brown). This is like many other diving and marine bird species, which use countershading as a method of camouflage. Voice: Although there are few records of black-vented shearwater calls, their vocalizations have been likened to a moaning growl, similar to the sound of a dentist's drill and suction. The black-vented shearwater only calls at night, when there is little to no moon. Vocalizations are believed to play a significant role in mating, as the species lacks sexual dimorphism, akin to the Manx shearwater.
ID text from Wikipedia, CC BY-SA 4.0
Manx Shearwater
Puffinus puffinus
The Manx shearwater is 30–38 cm (12–15 in) with a 76–89 cm (30–35 in) wingspan and weighs 350–575 g (12+1⁄2–20+1⁄2 oz). It has the typically "shearing" flight of the genus, dipping from side to side on stiff wings with few wingbeats, the wingtips almost touching the water. This bird looks like a flying cross, with its wings held at right angles to the body, and it changes from black to white as the black upper parts and white under sides are alternately exposed as it travels low over the sea. Voice: This shearwater is mainly silent at sea, even when birds are gathered off the breeding colonies. It calls on its nocturnal visits to the nesting burrows in flight, on the ground, and in the burrows, although moonlight depresses the amount of calling.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Black-vented Shearwater and Manx Shearwater.