66 USGS/BRD/ITR-2000-0012 



(Rodway et al. 1990b, 1992). A partial failure also 

 occurred in 1989. Large numbers of murre eggs had 

 been eaten by glaucous-winged gulls (Larus 

 glaucescens), but it was unknown whether predation 

 contributed to abandonment or occurred afterward 

 (Rodway 1990). Incubating murres that remained at 

 breeding sites sat tight on their eggs when approached 

 by bald eagles or peregrine falcons. Thus, it seemed 

 unlikely that avian predators were the sole cause of 

 failure. Large numbers of murres were killed by the 1988 

 Nestucca oil spill, but a distinct change in the breeding 

 colony at Triangle Island could not be detected 

 (Rodway et al. 1989, 1990b; Burger 1992). 



Overall Population Assessment 



Current Population Size and Distribution of 

 Breeding Colonies 



A complete assessment of the total size and 

 distribution of the overall breeding population of the 

 common murre in California, Oregon, Washington, and 

 British Columbia has been made only once, over a 2-year 

 period from 1988 to 1989. During this period, the overall 

 estimated breeding population was approximately 1 . 1 

 million breeding birds (Table 2.9; see Carter et al. 1995). 

 Several previous population estimates of common 

 murres for this portion of western North America were 

 lower and less reliable. Tuck (1961) roughly estimated 

 not more than 1 million murres for California and 

 Oregon without details, and it was not clear if breeding 

 and nonbreeding birds were included in the estimate. 

 Byrd et al. (1993) used a combination of 1979-89 data 

 and reported a total of about 826,000 breeding murres: 

 California (363,000 in 1979-80; Sowls et al. 1980), 

 Oregon (426,000 in 1988; R. W. Lowe, unpublished 

 data), Washington (3 1 ,000 in 1 978-79; Speich and Wahl 

 1989), and British Columbia (6,000 in 1988-89; 

 Campbell et al. 1990). However, large population 

 declines occurred in central California and Washington 

 between 1979 and 1989, which makes this combination 

 of data less reliable. Tyler et al. (1993) reported 810,500 

 breeding murres (minus British Columbia): California 



(35 1,000 in 1989; Carter etal. 1992), Oregon (438,100 

 in 1989; Briggs et al. 1992), and Washington (21,400 

 in 1989; Briggs et al. 1992). We relied on data largely 

 from the USFWS for murre numbers in Washington and 

 Oregon to maximize compatibility among data sets used 

 to generate population estimates. Rodway (1991) 

 reported 8,640 breeding birds for British Columbia; this 

 estimate was based on the same information as the 8,300 

 breeding birds estimated in this report. 



From 13.0 to 20.7 million breeding individuals, or 

 6.5 to 10.3 million breeding pairs, of common murre 

 have been estimated in the world, with 54-57% and 

 43-46% in the Pacific and Atlantic Oceans (including 

 adjacent areas of the Arctic Ocean), respectively 

 (Nettleship and Evans 1985; Byrd et al. 1993; Ainley et 

 al., in preparation). The breeding population in 

 California, Oregon, Washington, and British Columbia 

 (about 1.1 million breeding birds) constitutes 5-8% 

 and 13-28% of the breeding population size of the world 

 and the Pacific Ocean, respectively. 



The common murre is the most abundant breeding 

 species of seabird in central California, northern 

 California, and Oregon (Sowls et al. 1980; Varoujean 

 and Pitman 1980; Carter et al. 1992, 1995; Tyler et al. 

 1993; R. W. Lowe, unpublished data). Suitable habitat 

 (small, bare, nearshore rocks) is abundant and widely 

 distributed along these coasts. Habitat availability and 

 the ability of murres to exploit various abundant prey 

 resources in many different marine habitats near shore 

 and throughout the continental shelf have enabled 

 murres to exist in high abundance within this 

 geographic area. In Washington, Cassin's auklets, 

 rhinoceros auklets (Cerorhinca monocerata), and 

 glaucous-winged gulls are more numerous than murres 

 (Speich and Wahl 1989). In south-central California, 

 the Brandt's cormorant becomes the most numerous 

 species of breeding seabird and murres no longer breed 

 south of Monterey County (Hunt et al. 1980; Sowls et 

 al. 1980; Carter etal. 1992). Murres have achieved large 

 breeding populations at most colonies in northern 

 California and Oregon in recent decades, probably in 



Table 2.9. Total sum of common murres counted and numbers of breeding adults estimated in 

 California, Oregon, Washington, and British Columbia in 1 988-1 989. 



a Sum of whole-colony counts at all colonies in a geographic area. 



