BIOLOGY AND CONSERVATION OF THE COMMON MURRE 53 



(Briggs et al. 1992) in late June 1989. Owing to 

 numerous problems (i.e., different survey techniques 

 and incomplete surveys), data from these surveys are 

 not discussed in this chapter (see Appendix A). In 1995, 

 three replicate aerial surveys were conducted to 

 determine variability in counts over a four week period 

 (Table 2.6). Although a few individual colony counts 

 did show much variation (i.e., Colony numbers 219-003, 

 219-010, 219-026), overall variation among the 15 

 colonies was small (Lowe and Pitkin 1 996). 



The number of murres at sample colonies in Oregon 

 increased from 1988 to 1990, then declined slightly 

 before severe El Nino breeding conditions in 1993 

 (Figure 2.8; Appendix H). In 1993, warm marine waters 

 persisted along much of the Oregon coast, which 

 resulted in complete murre reproductive failure. Colony 

 abandonment began in late May, prior to the annual 

 aerial photographic survey in early June. Abandonment 

 of this magnitude had not been reported previously in 

 Oregon. Murres returned in large numbers in 1994 and 

 increased further in 1995. The effects of the 1982-83 El 

 Nino were apparently not as severe as in 1993; however, 

 reduced breeding success and. possibly, greater adult 

 and subadult mortality was observed (Hodder and 

 Graybill 1985; Bayer 1986b; Bayer etal. 1991). Effects 

 of the 1 992-93 El Nino did not result in large changes 

 in the numbers of breeding murres in Oregon. The 

 breeding population in Oregon has been relatively 



Seven colony formations occurred during 1988- 

 95 (Table 2.4). One colony formed in 1989 on Seal Rock 

 (Colony number 219-057) and persisted until 1991, but 

 was then abandoned, possibly because of disruptions 

 from Steller sea lions Eumetopias jubatus that "haul 

 out" on the rock (R. W. Lowe, personal observation). 

 Other colonies formed in 1990, 1991, and 1994 when 

 murre numbers in Oregon reached high levels. One 

 colony formed in 1993, during the 1992-93 El Nino, 

 when the number of murres attending colonies was at a 

 record low. Six of seven new colonies (i.e., except 

 Unnamed Rock, Colony number 219-036) were 

 established at rocks nearby (i.e., within 250 m) large 

 colonies, probably reflecting intercolony movements 

 within colony complexes. For example, colony 

 formation at Seal Rock occurred in close association 

 with the large colony complex at Three Arch Rocks 

 National Wildlife Refuge. Six of the seven colony 

 formations (i.e., except Seal Rock) also occurred in 

 conjunction with newly-formed colonies of Brandt's 

 cormorants. Colony formation at Unnamed Rock 

 (Colony number 219-036) in 1994-95 occurred 5-6 

 km from the next nearest active murre colony but also 

 was associated with nesting cormorants. Six new 

 colonies still existed in 1995 (i.e.. except Seal Rock), 

 despite poor breeding conditions associated with 

 elevated sea-surface temperatures since 1991 (R. W. 

 Lowe, unpublished data). 



