Fork-tailed Storm -Petrel (Oceanodroma furcata) 



Fork-tailed Storm-Petrels are small seabirds 

 often found far from land over the open ocean. 

 They usually feed at the ocean's surface on 

 plankton but are known to follow fishing vessels 

 and to feed on scraps and fishing offal. Although 

 the species occurs in California, its center of 

 abundance appears to be the Aleutian Islands and 

 the Gulf of Alaska (Sowls et al. 1978). 



Fork-tailed Storm-Petrels breed on offshore 

 rocks and islands safe from mainland predators. 

 Throughout their range they nest in both rocky 

 crevices and, to a lesser extent, burrows in soil. 



To avoid diurnal predators, colony activity 

 occurs during the darkest hours of the night. 

 Adults mate, exchange incubation and brooding 

 duties, and feed chicks only during the night, 

 remaining in the burrow or returning to offshore 

 waters by day. For this reason Fork-tailed Storm- 

 Petrels are rarely seen at the breeding colonies 

 during the day. Their nocturnal habits make 

 detection of colonies difficult and estimation of 

 populations imprecise. 



CALIFORNIA COLONIES 



Fork-tailed Storm-Petrels have been iden- 

 tified at six sites in California, all north of Eureka 

 (Harris 1974, this study). The largest of these, 

 Little River Rock (325 035), is inhabited by 

 approximately 200 birds. The population at 

 Castle Rock (325 006) is estimated at 100 birds 

 (Osborne 1972), and the other four colonies 



together probably contain fewer than 100 birds 

 (Harris 1974, present study). All major colonies 

 of Fork-tailed Storm-Petrels in California have 

 probably been found, but additional small colonies 

 may still exist. 



HISTORICAL STATUS AND VULNERABILITY 



Published data indicate that since the 

 1930's, Fork-tailed Storm-Petrels have disappeared 

 from three California sites and been found at an 

 additional four sites. A major colony of storm- 

 petrels was extirpated from Whaler Island 

 (325 045), Del Norte County, after construc- 

 tion of a breakwater to the island in the 1930's 

 (Osborne 1972). Clay and Dawson found 

 Fork-tailed Storm-Petrels nesting on Blank 

 Rock (325 023) in 1916 (Dawson 1923) but this 

 species no longer breeds there (Osborne 1972). 

 Soil erosion probably led to their disappearance 

 from these two islands. Fork-tailed Storm-Petrels 

 have recently been found on Little River Rock 

 (325 035), Prisoner Rock (325 027), and Tolowa 

 Rocks (325 007) (Osborne 1972, Harris 1974, 

 this study). These recent discoveries probably 

 reflect a more thorough search for nests rather 

 than an increase in population and colonization 

 of new sites. 



Fork-tailed Storm-Petrels readily desert 

 their nests if disturbed by humans during incuba- 

 tion or while parents are brooding recently hatched 

 chicks. Evidence from studies of an Alaskan 



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