northern California. 



Twelve of the 23 species discussed in this 

 catalog reach either the northern or southern 

 limits of their breeding ranges within California. 

 Elegant Tems breed only as far north as San 

 Diego Bay. Black Storm-Petrels, Brown Pelicans 

 and Xantus' Murrelets breed as far north as the 

 Channel Islands, although they are much more 

 abundant farther south. The breeding range of 

 Ashy Storm-Petrels is restricted to coasts between 

 northern Baja California, Mexico, and Marin 

 County in northern California. Fork-tailed 

 Storm-Petrels, Pelagic Cormorants, Common 

 Murres, Pigeon Guillemots, Marbled Murrelets, 

 Rhinoceros Auklets, and Tufted Puffins are all 

 cool water species and reach the southern limits 

 of their breeding range within California. Pelagic 

 Cormorants and Pigeon Guillemots breed as far 

 south as the northern Channel Islands, as did 

 Common Murres and Tufted Puffins until the 

 early part of this century. Breeding Common 

 Murres and Tufted Puffins can now be found only 

 as far south as Monterey County in central 

 California. Marbled Murrelets probably breed no 

 farther south than the coastal forests in Santa 

 Cruz County, although they have been observed 

 as far south as Point Sal during the breeding 

 season. Probably the southernmost breeding 

 location of the Rhinoceros Auklet is at Point 

 Arguello (501 Oil). The southern range limit of 

 breeding Fork-tailed Storm-Petrels lies in the 

 islands of Trinidad Bay. 



Point Conception and the northern Channel 

 Islands are considered the boundary zone between 

 warm and cold waters in California. There 

 is no clean division of water masses in this area, 

 however. The region is, instead, a complex 

 oceanographic zone. The principal oceanographic 

 components are a cold southerly-flowing offshore 

 current (the California Current), a cold northerly- 

 flowing offshoot of the California Current (the 

 Southern California Countercurrent), and a cold 

 southerly-flowing inshore current (the Southern 

 California Coastal Current), all of which are 

 separated in part by bodies of warm water. At 

 this complex junction of water masses, Black 

 Storm-Petrels, Brown Pelicans, Pelagic Cormorants, 

 Pigeon Guillemots, and Xantus' Murrelets reach 

 the limits of their breeding ranges. 



Populations of seabirds living at the edges of 

 their breeding ranges are often small. This is 

 best illustrated in California by Fork-tailed Storm- 

 Petrels, Black Storm-Petrels, and Tufted Puffins. 

 These populations may be particularly susceptible 

 to changing environmental conditions and distur- 



bance. If local extinction should occur, as it has 

 in the case of the Tufted Puffin in the Channel 

 Islands, re-establishment could take a very long 

 time. 



Breeding activity of seabirds in California is 

 related to the hydrographic cycle by its synchrony 

 with a period of upwelling that usually begins in 

 March. During this period, strong northwest 

 winds develop and surface waters along the 

 coast move southerly and offshore. Cold, high- 

 salinity waters upwell along the coast to replace 

 surface waters moving away from the shore. 

 Once these cold, nutrient-rich waters reach the 

 photosynthetic zone, they trigger a phytoplankton 

 bloom which in turn triggers an increase first of 

 zooplankton and later of fish and squid. Bolin and 

 Abbot (1963) have shown that in Monterey Bay, 

 phytoplankton begins increasing in late January 

 and peaks in June. Seabirds of all species in 

 California concentrate their breeding activites 

 from as early as late winter through June and 

 early July, coinciding with the time of peak 

 plankton production. 



Productivity of plankton along the coast 

 decreases in late summer and early fall during the 

 oceanic period of the hydrographic cycle (Bolin 

 and Abbot 1963). At this time of year, the 

 strong northwest winds abate. Cold, surface 

 waters sink and are replaced by warm, low- 

 nutrient waters from offshore. Lack of food at 

 this time of year may help explain the cessation 

 of breeding activity and the occurence of periodic 

 die-offs of young birds, especially Common 

 Murres. 



The intensity and duration of the upwelling 

 period may influence the number of birds breeding 

 and their productivity. This may explain the 

 decreases in numbers of Brandt's Cormorants 

 which we observed at many sites in California in 

 1980 from the numbers we observed in 1979, 

 which was apparently a banner year for seabirds 

 in California. 



During the fall and winter, warm, nutrient- 

 depleted waters intrude into the California coastal 

 zone. These coastal waters move slowly northward, 

 pushed by predominantly southerly winds to 

 form a countercurrent (Schwartzlose 1963). If, 

 during the following period of upwelling, north- 

 west winds are not strong and persistent, upwelling 

 will be weak. Water temperatures will be higher, 

 plankton productivity lower, and the numbers of 

 breeding seabirds and their productivity will 

 decline. Fluctuations in these oceanic conditions 

 occur yearly, so variation in the number of 

 breeding seabirds and their productivity is 



16 



