CalKornia Population 



Catalog Total 



704 birds 

 = nest sites 



Percent of California 

 Breeding Population. 



Breeding Chronology 



Northern California 



dutch- 2 3 > 



Incubation Period -25-30 day* 

 Nettling Period - 35 40 dayl 



W laying 



i 



adults pfMwit 



Farallon Islands 



Channel Island! 



(29) 



Jan.\ Feb. I Mar. | Apt. \Mty | June | July 1 Au. | Sep. | Oct. T No. 



Farallon Islands in the 1860's, possibly as a result 

 of too much human disturbance. A few birds 

 were seen in 1903, but oystercatchers were not 

 observed there on a regular basis until 1956. The 

 breeding population of Black Oystercatchers on 

 the Farallon Islands increased to 16 by 1959 and 

 to 40 in 1972 (Ainley and Lewis 1974). Since 

 that time the population has stabilized and 

 may be at its maximum (Ainley pers. comm.). 

 Historical population information for areas other 

 than the Farallon Islands is almost nonexistent. 

 Black Oystercatchers require clean and 

 undisturbed rocky coastlines for nesting and 

 feeding. To the extent that these areas are 

 disturbed by humans, reproductive success will be 

 reduced. Oil spills, which foul rocky coastlines 

 where oystercatchers feed, could seriously affect 

 the food supplies of this species, but losses of 

 birds from direct oiling would probably be low. 

 Long-term degradation of intertidal habitat would 

 almost certainly cause population declines. 



i'i 



1 



. n 



\Black Oystercatchers Photo by Ian C. Tait 



37 



