17% 



California Colonies 



Catalog Total 



363,154 birds 

 = colony sites 

 = former sites 



Percent of California 

 Breeding Population. 



Breeding Chronology 



(35) 



Clutch- 1 



Incubation Period -28-34 dyi 



Nettling Period - 2u 28 days 



(35) 



edulti preterit 



Channel Island! 



egg laying 



(29,31) 



No confirmed bnMdiny tine* 1912. 

 Cnph constructed from tittnot tggt 

 f/w Chlnnel tt/wtOt. 



hatching 

 ? 



fledging 



adulu present 

 7 7 



Jan. | Feb. | Mar. | Apr. | May | June | July 



. | Oct. | 



same Islands for other species. These islands are: 

 Sisters Rocks, Blank Rock (325 024), Pilot Rock 

 (325 026), and Cape Vizcaino (379 002). Murres 

 may have been present at Cape Vizcaino during 

 the years of Osborne's work but could have left 

 the colony prior to his survey in August. Second, 

 there are 1 4 breeding colonies of Common Murres 

 for which both Osborne and Reynolds (1971) and 

 we have estimates. Our estimates greatly exceed 

 theirs in all cases, usually by a factor of two, 

 three, four, or more. Even if the two-thirds 

 attendance factor is subtracted from our estimates, 

 our totals still exceed Osborne and Reynolds' in 

 all but two cases. In the two instances where ours 

 are lower, Castle Rock and Green Rock, the two 

 estimates are similar. 



Apparently murre numbers have been 

 increasing throughout much of this century. 

 Osborne (1972) found that the population of 

 Common Murres in the region from Cape 

 Mendocino to the Oregon border has increased 

 from a few thousand birds in the 191 0's to about 

 143,000 birds in 1970. The history of Common 

 Murre populations at two other sites also suggests 

 that numbers are increasing. Clay (unpubl. field 

 notes) makes no mention of Common Murres at 

 Flatiron Rock between 1910 and 1934, but 

 Osborne estimated that 10,000 birds were present 

 there in 1970. Our estimate for this site in 1979 

 is 24,000 birds. Clay (unpubl field notes) 

 estimated 2,000 birds at Green Rock in 1941, 

 compared to Osborne's estimate of 40,000 in 

 1970 and our estimate of 55,000 in 1980. 



Common Murres on the Farallon Islands are 

 also increasing in number but in this case the 



increase follows a documented severe population 

 reduction. Between 1854 and 1959 the population 

 dropped from 400,000 birds to between 6,000 

 and 7,000 birds. A commercial egg harvest and 

 oil pollution were the primary causes of this 

 reduction (Ainley and Lewis 1974). With strict 

 protection, the population increased to 20,500 

 birds in 1972 and to 60,000 birds or more at the 

 present time. 



Common Murres formerly bred on Prince 

 Island (501 004) in the Channel Islands but no 

 longer do so. Hunt et al. (1979) states, "Since 

 the tiny colony at Prince Island was so far south 

 of the nearest murre colony, it seems likely that 

 repeated visits by early egg collectors, coupled 

 with the slim possibility of recruitment from 

 other colonies, could have eliminated murres as a 

 breeding species. . . ." 



Nesting Common Murres are very sensitive 

 to disturbance by boats, low-flying aircraft, and 

 humans on foot. When disturbed, adults flush 

 from the colonies and may knock eggs and chicks 

 from nest sites. The remaining chicks and eggs 

 are subject to increased predation from gulls 

 and ravens. Common Murres are highly vulnerable 

 to oil contamination and were some of the most 

 frequently oiled birds in the 1971 San Francisco 

 oil spill (Smail et al. 1972). They are common in 

 the coastal zone of California throughout the year 

 and spend large amounts of time on the water. 

 They appear to be highly social during both the 

 breeding and non-breeding seasons and frequently 

 congregate on waters adjacent to their colonies. 

 Future oil spills along the California coast could 

 kill large numbers of this species. 



41 



