BIOLOGY AND CONSERVATION OF THE COMMON MURRE 69 



attended colonies during severe El Ninos in 1983-84 

 and 1992-93. These events probably caused lower prey 

 availability or accessibility over the short term (e.g., 

 Ainley and Boekelheide 1990). Resultant depressions 

 in reproductive performance apparently have not had 

 long-term effects on the size of the "core" populations 

 in northern California and Oregon. Few anthropogenic 

 factors have affected murres in Oregon and northern 

 California in recent decades except in fall and winter 

 when most Oregon birds move north to Washington 

 and British Columbia. Some Oregon birds undoubtedly 

 have been killed in gill nets and by oil spills in 

 Washington and British Columbia (especially the 1988 

 Nestucca and 1991 Tenyo Maru oil spills) between 

 1979-95. Yet, despite such deaths, the "core" of the 

 overall population did not change to a large degree. 

 The large population size and the wide dispersal of 

 anthropogenic deaths among many colonies may have 

 lessened effects on the Oregon population. 



To reach current population levels, murres in 

 northern California and Oregon had to recover over many 

 decades (mainly from the 1940s to the 1970s) from 

 extensive human impacts that occurred in the late 

 nineteenth and early twentieth centuries. As impacts 

 from native peoples and early settlers declined, the 

 numbers and range of breeding murres increased to the 

 current high population levels. During this period, 

 colony formations (including recolonization events) 

 occurred widely. Adequate prey resources, available 

 breeding habitat, and relatively low natural or 

 anthropogenic deaths must have existed for this recovery 

 to occur. In northern California, extensive recovery has 

 occurred in Del Norte and Humboldt Counties but 

 recovery is still occurring in Mendocino and Sonoma 

 Counties where recolonization events and population 

 increase are ongoing. 



In central California, historical effects by early 

 settlers reduced this population to low levels. 

 Extirpation of colonies in Sonoma and. possibly, 

 Mendocino counties may have caused the geographic 

 gap between murres breeding in central and northern 

 California. Colony extirpation was recorded at San Pedro 

 Rock and near extirpation at the South Farallon Islands. 

 By the early 1980s, many colonies had increased 

 substantially, but were still well below known historical 

 levels. As in northern California, adequate prey 

 resources, available breeding habitat, and relatively low 

 natural and anthropogenic mortality existed for this 

 limited partial recovery to occur. Breeding habitat at 

 the South Farallon Islands has been reduced from 

 historical conditions, thus, it is unlikely this colony 

 will ever return to levels reached in the early nineteenth 

 century. Declines between 1982 and 1989 occurred at 



all colonies in central California and one colony 

 (Devil's Slide Rock) was extirpated. Partial recovery in 

 central California between 1989 and 1995 has been 

 slow and limited, possibly reflecting the relative severity 

 of the original decline, as well as continuing effects. 

 Breeding success has remained high at the South 

 Farallon Islands (except during severe El Ninos) and is 

 not a factor impeding recovery at most colonies 

 (Hastings et al. 1997; Sydeman et al. 1997; McChesney 

 et al. 1998. 1999; M. W. Parker, unpublished data). 

 However, mortality from recent oil spills (e.g., 1996 

 Mohican, 1997-98 Point Reyes Tarball Incidents, and 

 1998 Command) and the recent resurgence of significant 

 deaths in gill nets in Monterey Bay have increased 

 anthropogenic impacts since 1995 (P. R. Kelly, personal 

 communication). 



In Washington, numbers of murres attending 

 colonies in 1979-82 reflected growth since the early 

 twentieth century. Decline and little recovery between 

 1982 and 1995 in Washington appear to have resulted 

 from severe effects (from natural and anthropogenic 

 factors) on the murre population over the long term 

 (Figure 2.16). Murre attendance at the largest colonies 

 in southern Washington (i.e.. Split Rock, Willoughby 

 Island, Grenville Arch, and Rounded Island) plummeted 

 to small numbers of irregularly-occurring birds and 

 evidence of reproductive effort and success has been 

 largely absent since the initial decline. Small colonies 

 in northern Washington also declined, but to a lesser 

 degree and have shown limited growth in recent years, 

 possibly because of intercolony movements from 

 southern Washington colonies. Massive decline and a 

 lack of recovery in southern Washington may be related 

 to the lower initial population size in Washington before 

 the decline (compared with populations in Oregon and 

 California), the high magnitude of natural and 

 anthropogenic impacts over an extended period of time, 

 and intercolony movements of birds to northern 

 Washington colonies. However, small numbers of birds 

 still attend traditional breeding colony locations in 

 southern Washington and some recovery may be 

 possible in the future. The likelihood of rapid natural 

 recovery in Washington is very low because of continued 

 anthropogenic and natural effects and the slow rate of 

 murre recovery documented at severely reduced colonies 

 elsewhere along the Pacific coast. 



Overall, murre numbers in central California and 

 Washington have declined substantially since the early 

 1980s and currently exist well below historical 

 population levels and distribution (Figure 2.16). Major 

 declines occurred rapidly between 1982-86. and low 

 numbers have remained over extended periods of time 

 following these declines. Although limited increase has 



