BIOLOGY AND CONSERVATION OF THE COMMON MURRE 67 



response to the relatively low levels of colony 

 disturbance and anthropogenic mortality, and excellent 

 prey conditions within the central part of the California 

 Current upwelling system (Briggs et al. 1987; Ainley 

 and Boekelheide 1990; Tyler et al. 1993; Manuwal and 

 Carter 2001). 



About 66% of the overall breeding population of 

 common murres (U. a. califomica) is present in Oregon 

 (Table 2.9). More than 420,000 murres were estimated 

 breeding along the central and north coasts of Oregon 

 with the largest colonies at Bird Rocks, Three Arch 

 Rocks, Two Arches Rock complex, and Gull and Colony 

 Rocks near Newport. The southern Oregon coast 

 contained approximately 290,000 breeding murres with 

 the largest colonies at Cat and Kittens, Gull Rock (Cape 

 Blanco). Orford Reef. Island Rock, Hubbard Mound 

 Reef, Mack Arch, and outer Whaleshead. Significant 

 numbers (24%) also bred in northern California, mainly 

 on several large offshore rocks in Del Norte and 

 Humboldt Counties (especially Castle Rock, False 

 Klamath Rock, Green Rock, Flatiron Rock, and False 

 Cape Rocks). Combined. Oregon and northern 

 California comprise the current population "core" or 

 90% of the breeding birds which form the geographic 

 center of the entire U. a. califomica population. This 

 "core" area is located in the central part of the California 

 Current upwelling system, characterized by strong and 

 persistent upwelling during the spring and summer 

 (Briggs et al. 1987; Tyler et al. 1993). Prey resources 

 and breeding habitat in the area appear to have been 

 sufficient to sustain this major part of the population 

 from 1979 to 1995. 



Historically, very large numbers of murres were 

 present in central California, which also is located within 

 the central part of the California Current upwelling 

 system (Briggs et al. 1987; Ainley and Boekelheide 

 1 990; Tyler et al. 1 993). In the early nineteenth century, 

 central California had a much larger proportion of 

 breeding murres before near extirpation of the immense 

 colony at the South Farallon Islands. This colony may 

 have totaled 1-3 million breeding birds at its peak. By 

 1989, the number of breeding murres in central 

 California was at the lowest recorded level between 1979 

 and 1995 and comprised only about 8% of the total 

 population of breeding murres (Table 2.9). In 1979-82, 

 more than twice as many murres bred in central 

 California than in 1989. The largest colonies were 

 present at the South Farallon Islands. North Farallon 

 Islands, and Point Reyes. Presently, the southernmost 

 colony in California is in central California at Hurricane 

 Point Rocks. In the past, murres bred as far south as 

 Prince Island in the Channel Islands off southern 

 California. 



The southern limit of the breeding range of the 

 common murre in the eastern Pacific Ocean is roughly 

 aligned with the southern edge of the California Current 

 upwelling system off southern California and western 

 Baja California, where colder subarctic waters are diluted 

 by warmer waters from the central ocean gyre (Tyler et 

 al. 1993). Several other alcids also reach their southern 

 limit in southern or central California (i.e.. pigeon 

 guillemot [Cepphus columba], marbled murrelet 

 [Brachyramphus marmoratus], rhinoceros auklet. and 

 tufted puffin) or their northern limit (i.e., Xantus's 

 murrelet [Synthliboramphus hypoleucus]: Hunt et al. 

 1980; Sowls et al. 1980; Carter et al. 1992; Gaston and 

 Jones 1998). A major change in climate, breeding 

 habitats, prey resources, and natural predators occurs in 

 this area, which affects breeding by several breeding 

 seabird species (Hunt et al. 1980; Briggs et al. 1987; 

 Carter et al. 1992; Tyler et al. 1993). In addition, large 

 populations of native peoples used mainly marine food 

 resources and probably prevented breeding in many 

 parts of the Channel Islands off southern California for 

 thousands of years (e.g., Glassow 1980) until they were 

 extirpated from the area in the mid-nineteenth century. 

 In the nineteenth and twentieth centuries, early European 

 and American settlers also affected seabird populations 

 in southern California and northwestern Baja California, 

 with egg-collecting activities, introduction of predators 

 to islands (McChesney and Tershy 1998). and other 

 activities. Thus, the southern limit of breeding murres 

 U. a. califomica may have occurred in the southern 

 California or possibly northwestern Baja California for 

 at least tens of thousands of years. 



Breeding murres in Washington represented less 

 than 1% of the total breeding population of U. a. 

 califomica in 1988-89 (Table 2.9) but were several 

 times more numerous between 1979 and 1982. The few 

 colonies in British Columbia also comprised less than 

 1% of total breeding population (Table 2.9). Most birds 

 in British Columbia bred at one isolated colony at 

 Triangle Island, at the north tip of Vancouver Island. 

 Other colonies are small, widely separated, and 

 irregularly attended. The northernmost colony of U. a. 

 califomica is located at the Kerouard Islands at the 

 southern end of the Queen Charlotte Islands. There is 

 no evidence that murres ever bred more widely in British 

 Columbia. 



A major change in breeding habitat occurs on the 

 west coast of Vancouver Island, British Columbia, where 

 most of the outer coast islands become forested, and 

 those that are not tend to be small, low and rounded, 

 and less suitable for breeding by murres and some other 

 seabirds (Beebe 1960; Campbell et al. 1990). In 

 comparison with Washington, Oregon, and California. 



