Black-vented Shearwater

This species is pelagic, occurring in the Pacific Ocean and the Gulf of California. It comes closer to land than most other shearwaters It nests predominantly on offshore islands off north and western Baja California, Mexico, namely Isla Natividad (95% of the nesting population), Isla de Guadalupe, and Islas San Benito. It is relatively common along the central and southern California coast during the colder months. The species has recently been observed nesting on Isla Rasa and Isla Partida in the Gulf of California, showing an expansion to their previously known breeding range. Black-vented shearwaters have been spotted as far north as British Columbia, but it is considered an "accidental visitor". Black-vented shearwaters prefer warmer waters, reportedly greater than 14 °C, but the species is relatively plastic in terms of habitat choice and foraging strategies. The species primarily inhabits waters over the continental shelf. Near breeding colonies, the sea floor drops off significantly as one moves farther from the coast, and some individuals are believed to forage in waters that reach depths of over 2 kilometers. This species does not migrate far and tends to stay relatively close to its breeding colonies year-round.

Black-vented shearwaters are nocturnal, with activity levels influenced by ambient light. This is theorized to be a strategy to avoid predation by diurnal predators such as the Western Gull (Larus occidentalis), as they experience the highest predation rates during daylight hours.

Vocalizations. 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.

Diet and Foraging. The black-vented shearwater is thought to feed mainly on small fish. Individuals have been recorded eating sardines, herring, anchovies and Mastegoteuthid squid. They are not attracted to chum, and don't tend to follow ships for food live some other marine avian species. Black-vented shearwaters forage closer to shore than many other pelagic bird species and tend to avoid extended foraging trips. Like other species in the Puffinus genus, black-vented shearwaters are free-divers. They are the best performing free-diver in the Puffinus genus, with a maximum dive duration of 88 seconds and maximum depth of 52 meters. …