Comments: PREDATION: Accidental or intentional introduction of predatory mammals to breeding islands is the most significant threat. Introductions of domestic cats and dogs, rats, mongooses, river otters and other ground predators on offshore nesting islands have decimated many populations (Quinlan 1983, Brown and Nettleship 1984). Even mice can kill adult storm-petrels (Sibley 2001). Some colonies in California destroyed by cats (Everett and Anderson 1991). Introduced foxes exterminated colonies on some islands in Alaska (Lensink 1984). Cattle, sheep and horses trample burrows and erode hillsides. Breeders also vulnerable to avian predators: gulls, jaegers, skuas, owls, hawks and corvids (Watanuki 1986, Sibley 2001). Increasing numbers of predatory gulls in the last century because of food available at landfills and dumps have probably impacted storm-petrel populations (Sibley 2001).
PESTICIDES AND POLLUTION: Ingestion of weathered crude oil did not affect chick growth, perhaps because normal diet contains n-hexanes similar to oil; long-term impacts of oil ingestion on survival and reproductive success unknown (Boersma et al. 1988). High concentrations of organochlorine pesticides such as DDE and polychlorinated biphenyls (PCBs) have been found in eggs and adult tissue, but impact is unknown; significant egg-shell thinning has not been documented (Ohlendorf et al. 1978, Henny et al. 1982, Boersma 1986b). Plastics commonly ingested but may be expelled when birds regurgitate (Boersma 1981).
HUMAN DISTURBANCE: May be disturbed by campers, researchers, and aircraft bombing/testing (Buckley and Buckley 1984). Adults will desert nest if handled frequently (Boersma et al. 1980). At sea, attracted to lights from boats and may collide (Bent 1922).
CLIMATE CHANGE: Shifts in oceanic circulation patterns which alter food supplies and distribution have recently been tied to climatic changes. A possible example of impact is reduction by 90% of Sooty Shearwaters (Puffinus griseus) in the eastern North Pacific over the last 20 years (Sibley 2001). On the Barren Islands, chicks grew faster in the 1970s and 1980s than in the 1990s, and Boersma and Parrish (1998) presented evidence that chick growth is adjusted to changing resource availability, suggesting even small climate changes can impact demographics.
