Hydrobates leucorhous

Formerly (AOU 1983, 1998) included only the single species H. pelagicus, but genetic data (Penhallurick and Wink 2004, Robertson et al. 2011, Wallace et al. 2017) indicate that Oceanodroma as previously constituted was paraphyletic with respect to Hydrobates, resulting in the transfer of all species of Oceanodroma to Hydrobates, as in Dickinson and Remsen (2013) (AOS 2019).

Oceanodroma leucorhoa socorroensis, and O. l. cheimomnestes are now recognized as distinct species based on differences in vocalizations and morphology (Ainley 1980 in AOU 2016). Over the years, taxonomy has been confused and controversial (Huntington et al. 1996, AOU 1998, Sibley 2001). As of 2016, only two subspecies are recognized; Oceanodroma leucorhoa leucorhoa, O. l. chapmani. O. l. leucorhoa is found in the North Pacific and Atlantic Oceans, including Alaska, and is the largest of the subspecies. Possible incipient speciation (see Huntington et al. 1996 for discussion).

Some authors have regarded O. leucorhoa and O. monorhis as conspecific.

Large nesting range; abundant; populations appear to be increasing.

Breeding range in the northwestern Pacific Ocean extends from the Commander Islands south to the Kuril Islands and Hokkaido, Japan (AOU 1998). Breeding range in the eastern Pacific Ocean includes southern Alaska (including the Aleutian Islands), British Columbia, Washington, Oregon, California, and Baja California (Los Coronados, San Benito, and Guadalupe Islands, and Alijos Rocks). Breeding range in the western Atlantic Ocean extends from southern Labrador to Maine (Casco Bay) and Massachusetts (Penikese Islands). Breeding range in the eastern Atlantic Ocean includes Iceland, Faeroe Islands, Norway, Scotland, and Ireland (AOU 1998).

Southern Hemisphere: Potential for colonizing Southern Hemisphere: New Zealand and South Africa. Whittington et al. (2001) reported the first confirmed breeding (20 pairs) on Dyer Island off the coast of South Africa (AOU 1998).

This storm-petrel ranges at sea in the Pacific Ocean from the breeding areas south to the Hawaiian, Revillagigedo, and Galapagos lands, and in the western Pacific to Indonesia and New Guinea; and in the Atlantic Ocean south along both coasts to Florida, the West Indies, Caribbean Sea, Brazil, and South Africa, rarely but regularly also to the west coast of Greenland (AOU 1998).

Casual occurrences extend to the west coast of Greenland and eastern Atlantic islands, Mediterranean Sea, and western Europe (Huntington et al. 1996, AOU 1998).

This species is represented by a large number of occurrences (subpopulations).

Predation: Introduction (accidental or intentional) of predatory mammals to islands is the most significant threat. Storm-petrels have suffered from introductions of domestic cats and dogs, rats, mongoose, and other ground predators on many offshore nesting islands (Brown and Nettleship 1984). Even mice can kill adult storm-petrels (Sibley 2001). Introduced foxes and rats exterminated colonies on some islands in Alaska (Lensink 1984). Cattle, sheep, and horses trample burrows and erode hillsides. Known native predators include short-eared owl (Holt 1987) and slaty-backed gull (Watanuki 1986). Increasing presence of predatory gulls and some raptors near landfills and dumps in the last century has probably impacted storm-petrel populations (Sibley 2001).

Pesticides: Pesticides and contaminants such as DDE and polychlorinated biphenyls (PCBs) were present in tissue samples collected in eastern Canada from 1968 to 1984 (Pearce et al. 1989). Long-term data from this study, however, showed decreasing levels of contaminants in seabird tissue samples.

Pollution: Plastics are commonly ingested by storm-petrels but may be expelled when the birds regurgitate (Boersma 1981). Ingested plastic particles may impede digestion (Blight and Burger 1997). Reproductive success may be reduced by exposure to crude oil or oil emulsion (Butler et al. 1988).

Disturbance at colonies: Leach's storm-petrels may be disturbed by picnickers, researchers, and aircraft bombing/testing (Buckley and Buckley 1984), as well as fires, livestock grazing, and introduced predators.

Climate change: Shifts in oceanic circulation patterns that alter seabird food supplies and distribution have been tied to climatic changes; a recent example of this impact may be the 90% reduction of sooty shearwaters (Puffinus griseus) in the eastern North Pacific over the last 20 years (Sibley 2001).