common. 



More prolonged changes in climate can also 

 influence breeding populations of seabirds. 

 Cassin's Auklets, now the most abundant seabirds 

 on the Farallon Islands, were rare on those islands 

 in the mid-1 800's (Ainley and Lewis 1974). 

 These auklets are cold water birds found from the 

 Pacific coast of Baja California, Mexico, north to 

 the Gulf of Alaska and the Aleutian Islands. In 

 California, the breeding period of this species 

 coincides with the period of upwelling of cold, 

 nutrient-rich waters when zooplankton is most 

 abundant. According to Hubbs (1948), the ocean 

 climate from 1853 to the 1870's was dominated 

 by a northward intrusion of warm water. Ainley 

 and Lewis (1974) believe this northward intrusion 

 of warm water extended as far north as the San 

 Francisco-Farallones region and may explain the 

 scarcity of Cassin's Auklets on the Farallon 

 Islands during that time. Additional evidence of 

 this was found during two other warm water 

 periods in recent years when Cassin's Auklet 

 productivity on the Farallon Islands was signif- 

 icantly lower than in cold water years (Ainley and 

 Lewis 1974). 



Gradual changes in seabird populations may 

 also occur in response to the gradual degradation 

 and formation of nesting habitat. Many islands 

 and rocks along the California coast are eroding 

 away. During this process, the habitat changes 

 and it may become more suitable to some species 

 and less suitable to others. For example, younger 

 islands with deep soil layers are preferred by 

 burrowing species such as storm-petrels, Cassin's 

 Auklets, Rhinoceros Auklets, and Tufted Puffins. 

 As the soil erodes away, islands become less 

 suitable to these species. Cormorants may 

 colonize the barer regions of the island and speed 

 soil and vegetation loss. Once an island is stripped 

 of soil and vegetation it may be suitable only 

 for cormorants, murres, and, to a lesser extent, 

 Western Gulls. 



Examples of nesting islands in different 

 stages of their evolution are evident up and down 

 the California coast. Point Sur, at the north end 

 of Big Sur, and Trinidad Head in northern 

 California are obvious islands-in-the-making, 

 although they are still attached to the mainland. 

 Pewetole Island, north of Trinidad Head, is a 

 forested island recently cut off from the mainland, 

 still accessible to predators^ 1<^ tide, and at the 

 present time inhabited onty by Black Oyster- 

 catchers. This island appears to offer excellent 

 petrel habitat and could become an important 

 colony once the channel between it and the 



mainland deepens. Little River Rock (325 035) is 

 a treeless but heavily vegetated island in northern 

 California, accessible to humans by wading at low 

 tide. Little River Rock is the largest storm-petrel 

 colony in California but it has recently been 

 colonized by Double-crested Cormorants which 

 are degrading the habitat for burrowing species 

 (Harris pers. comm.). 



Flatiron Rock (325 023) is an almost bare 

 island in northern California presently inhabited 

 by large numbers of Common Murres, Brandt's 

 Cormorants, Western Gulls, and a very few Pigeon 

 Guillemots and Tufted Puffins. Clay (unpubl. 

 field notes) in 1911 reported Tufted Puffins as 

 numerous there and also found nests of Pigeon 

 Guillemots, Cassin's Auklets, and Leach's Storm- 

 Petrels. We found the burrow nesting habitat to 

 be poor in quality and used by few birds during 

 our visits to the island in 1980. 



These examples show a continuum in the 

 evolution of seabird nesting habitat from future 

 islands, to new islands with deep soil, to older 

 islands with less soil, suitable only for surface 

 nesting seabirds, and finally to wave-washed rocks 

 unsuitable for nesting. 



Seabirds themselves can be active agents in 

 the evolution of nesting habitat. Pelicans, cormo- 

 rants and gulls remove plants for nest building 

 and their excrement sometimes kills vegetation. 

 Burrowing species contribute to the destruction 

 of their own nesting habitat by digging burrows 

 and removing soil. Puffin Island, in the Chamisso 

 Island National Wildlife Refuge in Alaska, is a 

 vivid example. There, a burrowing population of 

 Horned Puffins has created long, deep furrows in 

 the sod where burrows have collapsed, accelerating 

 recession of the vegetative cover from the nesting 

 area and hastening the removal of soil through 

 erosion (DeGange and Sowls unpubl. data). 



Seabird numbers and productivity vary 

 naturally from year to year and also over longer 

 periods of time. Man's activites have in the 

 past had largely adverse effects on California's 

 seabirds. Additional conflicts in the future are 

 likely, but still avoidable. We hope that planners 

 will carefully consider the welfare of seabirds 

 when making coastal policy decisions. To this 

 end, the catalog of California seabird colonies will 

 be useful. Seabird populations in this state can 

 flourish indefinitely, as long as they can satisfy 

 their basic needs - food, sufficient habitat, a clean 

 environment, and freedom from disturbance. In 

 this sense, "management" of seabirds" should be 

 directed towards meeting these needs. 



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