Ashy Storm-Petrel (Oceanodroma homochroa) 



World Breeding Range 



Ashy Storm-Petrels, like other storm-petrels, 

 are diminutive birds well suited to oceanic life. 

 Their breeding range overlaps with that of their 

 close relative, the Leach's Storm-Petrel, but they 

 occupy different feeding niches. The Ashy 

 Storm-Petrel forages in the waters of the California 

 Current, just off the continental shelf, while the 

 Leach's Storm-Petrel feeds over a vast pelagic 

 range (Ainley et al. 1974). 



Ashy Storm-Petrels and other members of 

 the family Hydrobatidae feed on small inverte- 

 brates and fish caught at the ocean surface. All 

 hydrobatid young are fed a peculiar smelling oil 

 which the adults regurgitate. This oil, or "petro- 

 leum," as labelled by Grinnell (1897), provides a 

 concentrated energy source for growth of the 

 young and allows adults to carry more food than 

 if they return with whole prey. 



Ashy Storm-Petrels usually nest in natural 

 rock crevices, although the Farallon Island 

 population uses rock walls and building foundations 

 as well (Ainley et al. 1974). Adults are nocturnal 

 at the colonies and may only return with food 

 every few nights. Foraging trips lasting several 

 days probably allow storm-petrels to feed over a 

 larger range to optimize their effort. 



The nocturnal habits of Ashy Storm-Petrels 

 may serve to reduce predation by normally 

 diurnal Western Gulls. On the Farallon Islands, 

 Ainley et al. (1974) foundthat only one percent 

 of the storm-petrels were taken by Western Gulls 

 each year. In addition, Ashy Storm-Petrel young 



fledge late in the year after many of the gulls have 

 left the Farallon Islands and by this strategy may 

 avoid a potentially serious post-fledging mortality. 



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CALIFORNIA COLONIES 



With the exception of one small colony in 

 the Los Coronados Islands of Mexico, estimated 

 to contain about six birds (Jehl pers. comm.), the 

 entire known world's population of Ashy Storm- 

 Petrels inests on islands off the California coast. 

 More than 75 percent (4,000 birds) of the recorded 

 population nests on the Farallon Islands (429 

 012). The remainder of the population, except 

 for a small colony at Bird Rock (404 010), nests 

 in the Channel Islands. 



Nine colony sites have been found in the 

 Channel Islands. Major colonies are located on 

 Prince Island (501 004) with 600 birds, Castle 

 Rock (501 005) with 200 birds, and Santa 

 Barbara Island (524 009) with 250 birds. Addi- 

 tional small colonies are located on San Miguel 

 Island (501 006), and small islets offshore of 

 Santa Barbara and Santa Cruz Islands. Although 

 additional small colonies of Ashy Storm-Petrels 

 may exist in the Channel Islands and elsewhere 

 along the California coast, the largest colonies 

 have probably been identified. All identified 

 colonies together contain approximately 5,200 

 birds. It seems unlikely that the population 

 exceeds 10,000 birds, allowing for possible under- 

 estimation of known colonies and the existence 



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