BIOLOGY AND CONSERVATION OF THE COMMON MURRE 47 



21 August 1980(Sowlsetal. 1980, unpublished survey 

 data). 



Sowls et al. (1980) reported four suspected new 

 colonies in 1979-80 not thought to have been present 

 in 1969-70 (Osborne and Reynolds 1971; Osborne 

 1972): Sister Rocks, Blank Rock. Pilot Rock, and Cape 

 Vizcaino. However, we considered that some or all of 

 these colonies may have been overlooked in earlier 

 surveys (i.e., these focused on large colonies) or sporadic 

 attendance may have reflected intercolony movements 

 within colony complexes. For instance, murres were 

 noted by other observers at Blank Rock in March 1965 

 and at Pilot Rock in 1966-69 (Appendix B). No birds 

 were reported at Blank Rock in 1979. but small numbers 

 were present in 1980-81. On the other hand. Cape 

 Vizcaino was surveyed in August 1969, at a time when 

 breeding may have been finished. We considered small 

 numbers of murres attending Sister Rocks in 1980-82 

 to represent an active colony because about 30 

 "brooding" birds were reported on 20 June 1980 and 

 birds were present on 19 May and 25 July 1980 (Sowls 

 et al. 1980, unpublished survey data). However, no birds 

 were reported there on 22 May 1979 and breeding has 

 not been confirmed subsequently. 



Overall, the increase in the northern California 

 population (1979-82) seemed to reflect continuation 

 of a long-term increase over several decades, owing to a 

 reduction in levels of human disturbance (Appendix 

 B). For instance, from 1970 to 1979, murre counts 

 increased at Castle Rock (i.e., from about 32,000 to 

 76,000 birds). Green Rock (i.e., from about 20.000 to 

 25.000 birds), and Flatiron Rock (i.e., from about 5,000 

 to 15,000 birds). Although counting techniques were 

 not directly comparable between 1970 and 1979. 

 substantial increase seemed to have occurred during 

 this extended period with continued increases through 

 1982. 



Between 1979 and 1989, little change was noted at 

 many colony complexes in northern California (Figures 

 2.5 and 2.6). A notable exception was Castle Rock where 

 numbers were much lower in 1986 and 1989 than in 

 1979-82 (Figure 2.5: Appendixes C and D). However, 

 upon inspection of archived aerial photographs (J. E. 

 Takekawa, H. R. Carter, and K. T. Briggs. personal 

 communication), there was no visible difference in 

 breeding densities or in breeding areas used (Takekawa 

 et al. 1990). Differences seemed to be related primarily 

 to different aerial survey methods used at this large 

 colony (see Appendix I: Figure 1-20). In 1979-82, few 

 photographs were taken per survey and numbers were 

 estimated roughly within blocks of high-density murres. 

 In 1986 and 1989, many photographs per survey 



provided better viewing of all parts of the colony and 

 all murres were counted individually. Survey and 

 counting methods used in 1986 and 1989 were 

 considered to more accurately reflect colony size 

 (Takekawa et al. 1990; Carter et al. 1992). The severe 

 1982-83 El Nino may have caused lower attendance 

 and breeding success at Castle Rock in 1983, but the 

 lack of a large or sustained decline at most other colonies 

 from 1982 to 1986 supports the view that Castle Rock 

 probably had not declined to a large degree. 



In 1983, establishment of the California Islands 

 Wildlife Sanctuary, which prohibited disturbance to 

 seabirds and marine mammals, may have reduced human 

 disturbance at several murre colonies, especially in the 

 Trinidad and Cape Mendocino colony complexes. In 

 1989, total numbers in the Trinidad complex were 

 similar to 1980-81. (Appendixes C and D). Continued 

 variation in murre numbers occurred at Redding Rock 

 (i.e., low numbers in 1986 and high numbers in 1989). 

 probably reflecting continued disturbance by U.S. Coast 

 Guard personnel. Of interest. Redding Rock was not 

 specifically identified as "withdrawn for lighthouse 

 purposes" when the California Islands Wildlife 

 Sanctuary was created in 1983. The Cape Mendocino 

 and Cape Vizcaino complexes increased from 1 982 to 

 1989. Most growth within the Cape Vizcaino complex 

 occurred at the newly recolonized Rockport Rocks 

 colony where breeding was first noted in 1989. 



The northern California population remained 

 relatively stable from 1979 to 1989 (Figure 2.6; 

 Takekawa et al. 1990; Carter et al. 1992: Appendix H). 

 In fact, total whole-colony counts (excluding Castle 

 Rock) were similar in 1982 (88.962) and 1989 (92.080). 

 By not considering early survey problems to be 

 significant at Castle Rock nor examining trends at other 

 colonies, other sources have indicated that the northern 

 California population (or Castle Rock colony) declined 

 greatly between 1979 and 1989 (Ainley et al. 1994; 

 Jaques and Strong 2001 ). However, as noted above, the 

 large change in numbers at Castle Rock between 1982 

 and 1986 was not visually evident in aerial photographs 

 (Takekawa et al. 1990). In central California, major 

 declines between 1982 and 1985-86 were obvious in a 

 comparison of aerial photographs (Carter and Ainley 

 1987; Takekawa et al. 1990; McChesney et al. 1998, 

 1999). We considered data at Castle Rock to be 

 reasonably comparable within the periods 1979-82 and 

 1986-89. but not between these periods. Additional 

 efforts are needed to evaluate comparability of data sets 

 and trends at Castle Rock, especially reexamining 

 1979-82 photographs and counting archived aerial 

 photographs for several years between 1985 and 1995 

 (Appendixes C and D). 



