Black-vented Shearwater Puffinus opisthomelas Scientific name definitions

The Cornell Lab of Ornithology dedicates this account in honor of Brandon Southall, member of the Lab of Ornithology's Administrative Board.

This small shearwater, endemic to the Pacific Coast of North America, is named for the dark undertail coverts that separate it from other closely related “white-vented shearwaters” in the genus Puffinus. Like most other Puffinus species, the Black-vented Shearwater is nocturnal when visiting land. When sandy substrate is not available for burrowing, this species lays its single white egg at the back of a natural rock crevice. Appearing deserted during the day, nesting colonies come alive with the moaning wail of shearwaters during moonless nights.

In contrast to its more pelagic relatives, the Black-vented Shearwater is a coastal species, most frequently observed within 25 km of shore. It is the only shearwater that breeds at sites within the California Current, nesting on remote desert islands near productive upwelling zones off the west coast of Baja California, Mexico. In feeding, this shearwater plunges from just above the sea surface or submerges from afloat and dives to depths over 20 m to catch schooling fishes, squid, and probably crustaceans.

A paucity of information on the breeding biology and status of this bird led the International Union for the Conservation of Nature (IUCN) to list it as a Species of Concern and Mexico to list it as Threatened. Although recent information shows that populations are larger than previous estimates suggested, more than 95% of the breeding population occurs solely on Natividad Island, Baja California Sur, Mexico. In addition, all breeding locales have historically had introduced mammals and permanent human residents, a situation that has reduced available nesting habitat and increased adult mortality.

The coastal foraging habits of this species and its erratic postbreeding dispersal stand in contrast with many other Puffinus shearwaters, making this an interesting species for study. Very little is known about the bird, owing primarily to its breeding on remote islands, and its nocturnal, burrow-nesting habits. Besides a collection of egg records from the three breeding islands, knowledge of reproduction is limited almost entirely to Natividad Island (Keitt 1998 Keitt, B. S. (1998). Ecology and conservation biology of the Black-vented Shearwater (Puffinus opisthomelas) on Natividad Island, Vizcaino Biosphere Reserve, Baja California Sur, Mexico. Master's Thesis, Univ. of California, Santa Cruz. Close ). However, postbreeding movements northward are well known from observations off California, and these movements have been linked to ocean temperatures (Ainley 1976 Ainley, D. G. (1976). The occurrence of seabirds in the coastal region of California. Western Birds 7:33–68. Close , Briggs et al. 1987b Briggs, K. T., W. B. Tyler, D. B. Lewis, and D. R. Carlson (1987). Bird communities at sea off California: 1975 to 1983. Studies in Avian Biology 11:1–74. Close , Tyler et al. 1993 Tyler, W. B., K. T. Briggs, D. B. Lewis and R. G. Ford. (1993). "Seabird distribution and abundance in relation to oceanographic processes in the California Current system." In The status, ecology and conservation of marine birds of the North Pacific., edited by K. Vermeer, K. T. Briggs, K. H. Morgan and D. Siegal-Causey, 48-60. Ottawa: Can. Wildl. Serv. Spec. Publ. Close , Ainley et al. 1995d Ainley, D. G., R. R. Veit, S. G. Allen, L. B. Spear, and P. Pyle (1995). Variations in seabird numbers in the California Current, 1986–1994. California Cooperative Oceanic Fisheries Investigations Report 36:72–77. Close , Veit et al. 1996 Veit, R. R., P. Pyle and J. A. McGowan. (1996). Ocean warming and long-term change in pelagic bird abundance within the California current system. Marine Ecology Progress Series 139:11-18. Close ). Future research on foraging energetics and food provisioning of young of this coastal species should prove rewarding.