The Black-vented Shearwater is a small, nocturnal seabird found in the eastern Pacific, known for its dark brown upperparts, speckled white underparts, and exceptional free-diving abilities. It primarily inhabits waters over the continental shelf, preferring warmer seas, and nests in burrows on offshore islands off Baja California and the Gulf of California.
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Black-vented Shearwater in flight over the Pacific, underside view.
Learning lesson · openly licensed photographs, labelled by BirdBot; labels checked against the cited sources and approved by AI
Dark brown upperparts: dark brown head, back and upperwings. Dingy head and throat: brown smudging around the head and throat. Smudgy white underparts: white below with brown specks and smudges. Dark under the tail: dark under the base of the tail. Dark vent separates it from the whiter Manx Shearwater.
Manx Shearwater is rare off the west coast and whiter below.
Sources: Audubon Guide to North American Birds: Black-vented Shearwater · Wikipedia: Black-vented shearwater (revision 1359377586)
Photo: Madeleine Claire, CC BY 4.0, via Wikimedia Commons; labels added by BirdBot.
Adults measure 30–38 cm in length with a wingspan of 76–89 cm and weigh approximately 400 g. The species exhibits countershading, a common camouflage strategy in marine birds, with dark brown heads and dorsal plumage contrasting with lighter ventral plumage that is often white with specks and smudges of brown. There is no sexual dimorphism; males are only slightly larger than females, a difference that is minimal in the field. Juveniles resemble adults but are darker and more contrasted, while chicks hatch with grey down feathers that lighten over time.
This pelagic species occurs in the Pacific Ocean and the Gulf of California, staying relatively close to its breeding colonies year-round rather than undertaking long migrations. It prefers warmer waters, reportedly above 14 °C, and primarily inhabits waters over the continental shelf. Notably, it forages closer to shore than many other shearwaters, sometimes in waters reaching depths of over 2 kilometers near breeding colonies. Its breeding range includes Isla Natividad (home to about 95% of the nesting population), Isla de Guadalupe, and Islas San Benito, with recent observations of nesting on Isla Rasa and Isla Partida in the Gulf of California.
Black-vented Shearwaters are nocturnal, a behavior theorized to help them avoid diurnal predators like the Western Gull. They are exceptional free-divers, the best performers in the Puffinus genus, with a maximum dive duration of 88 seconds and a depth of 52 meters. During the breeding season, they dive even deeper. Their diet consists mainly of small fish such as sardines, herring, and anchovies, as well as Mastegoteuthid squid. Unlike some other marine birds, they do not follow ships or respond to chum.
With few recorded calls, their vocalizations are described as a moaning growl, similar to a dentist's drill and suction. They call only at night, particularly when there is little to no moonlight. These calls play a significant role in mating, helping individuals recognize each other in the absence of visual sexual dimorphism.
Colonial nesters, they construct burrows in sandy soil or use pre-existing rock crevices, particularly on San Benito Island. Burrow formation is suggested to occur between late November and January. Clutches usually contain one egg, with occasional second eggs likely resulting from egg-dumping or leftovers from a previous season. Both parents share incubation duties in shifts of three to five days, with a total incubation period of about 49 days. Chicks are altricial and require significant parental care.
Because this species is nocturnal and sensitive to light, the best ethical observation strategy is to view them from a distance during low light or night. As a pelagic species that forages near shore, observation is typically conducted from boats or stable shorelines rather than from land-based dark locations. Avoid using bright lights that could disturb their natural behavior or increase their vulnerability to predators. Observing from a boat or shoreline during the colder months, when they are relatively common along the central and southern California coast, offers the best chance for a respectful encounter.
Note: Behavioral and diving claims are summarized from the pinned Wikipedia revision, which cites underlying primary studies. For detailed acoustic or taxonomic comparisons, consult the primary literature referenced in the BirdLife factsheet.
