California Colonies 



Catalog Total 

 15,870 birds 

 = colony sites 



12% 



Percent of California 

 Breeding Population. 



Breeding Chronology 



(35,37,39) 



Farallon Islands 



adults prBiont 



1 



hatching 



(1) 



(29) 



Jin. | Feb. ] Mac. | Apr. | May I Jun | Julvl Au> j Sp. | Oct. j No. 



HISTORICAL STATUS AND VULNERABILITY 



Detailed information on the historical status 

 of Pelagic Cormorants exists for only limited 

 portions of the California coast. In the Channel 

 Islands there has been little change in either total 

 number or distribution during the last century 

 (Hunt et al. 1979). In contrast, Pelagic Cormorant 

 populations on the Farallon Islands (429 012) 

 -declined greatly in size during the 1850 to 1900 

 period of egg collecting (Ainley and Lewis 1974). 

 The population has been recovering throughout 

 this century and is still increasing in 1980 (Ainley 

 pers. comm.). 



Historical population estimates for northwest 

 California are available from Osborne and 

 Reynolds (1971), although differences in time of 

 survey and survey technique limit comparisons 

 with our 1979-80 data. The tendency of Pelagic 

 Cormorants to move nest sites in succeeding years 

 (Benz and Garrett 1978, Nysewander and 

 Barbour 1979), makes surveys of large areas 

 desirable for this species. 



Shoreline use and development pose a great 

 threat to Pelagic Cormorants in California. 

 Cormorants can be disturbed by any human 

 activity near colonies. Approach to nesting birds 

 by boats, planes, and humans on foot may force 

 adults off their nests, leaving eggs and young 

 chicks unprotected. Chicks and eggs may be 

 knocked from nests and predation by Western 

 Gulls and Common Raven may increase following 

 the adults' panicked retreat. 



Pelagic Cormorants, like other members of 

 the order Pelecaniformes, may be vulnerable to 

 pesticide pollution. The egg shell thinning, egg 

 breakage, and subsequent population declines 

 experienced by both Brown Pelicans and Double- 

 crested Cormorants in | southern California (Gress 

 et al. 1973) are yet undocumented for Pelagic 

 Cormorants (Hunt et al. 1979). 



Oil spills in California have resulted in few 

 known cormorant deaths to date (Aldrich 1938, 

 Moffitt and Orr 1938, Smail et al. 1972, and 

 Berkner pers. comm.). Because of their widespread 

 distribution and ability to shift colony sites, Pelagic 

 Cormorant populations are relatively resistant to 

 localized oil slicks. Individual cormorants may 

 avoid surface oil (Berkner pers. comm.), and their 

 habit of spending nights and much of the day 

 roosting on rocks further reduces vulnerability to 

 oil pollution (Smail et al. 1972). 



35 



