34 USGS/BRD/ITR-2000-0012 



whole-colony counts were conducted using 1 979-95 data. Complete data for all colonies were available only 

 in 1988-89 when the breeding murre population was estimated to be 1.1 million, about 5-8% of the world 

 population and 13-28% of the Pacific Ocean population. A summary of various natural and anthropogenic 

 factors affecting murre populations in western North America since 1 800, and particularly in 1 979-95, also 

 is provided. 



A relatively good history exists for murre colonies in central California. The well-known colony at the 

 South Farallon Islands may have numbered 1-3 million birds in the early 1 800s. Egging and human disturbance 

 throughout most of the nineteenth century, plus mortality from oil pollution in the early twentieth century, 

 caused the near extirpation of this colony by the 1930s. Since the 1950s, this colony has grown and, by the 

 early 1980s, again was the largest colony in central California. Two other large colonies also are present in 

 central California at the North Farallon Islands and Point Reyes. In the early twentieth century, Prince Island 

 in southern California was the southernmost breeding colony of U. a. califomica, but the colony was 

 extirpated in about 1912. Hurricane Point Rocks in central California is now the southernmost colony. In 

 1980-82, the central California breeding population was estimated at 194,000-224,000 breeding birds at nine 

 active colonies. From 1979 to 1989, this population declined 9.9% per annum (P = 0.002) because of 

 mortality from gill nets and oil spills, in concert with detrimental effects from the severe 1982-83 El Nino. All 

 colonies declined significantly and the Devil's Slide Rock colony was extirpated. In 1 989, the population was 

 estimated at 90,200 breeding birds at 8 active colonies (i.e., 8% of the U, a. califomica population). From 

 1985 to 1995, the population increased 5.9% per annum (/> = 0.002), mostly since 1989-90, but had only 

 partly recovered to 1979-82 levels by 1995. Increase since the late 1980s has occurred despite continuing 

 anthropogenic impacts and low reproduction during the severe 1992-93 El Nino. The Devil's Slide Rock 

 colony did not recover between 1986 and 1995, but breeding has been restored in 1996-2000, using social 

 attraction techniques. 



In northern California, limited historical data indicated that murre colonies were heavily affected by early 

 settlers in the late nineteenth century, as well as oil pollution in the early twentieth century. Only two colonies 

 (i.e., Castle and Green Rocks) were specifically known prior to the late 1 940s. Detrimental effects apparently 

 lessened in the mid-twentieth century, allowing substantial population growth over several decades since the 

 1 930s, including many recolonization events prior to the 1 970s. Little change in available population numbers 

 occurred from 1979 to 1989, which suggests a possible leveling of population numbers and little or no 

 long-term detrimental effects from the 1982-83 El Nino. Lower numbers at Castle Rock in 1986 and 1989 

 appear related to differences in survey techniques. In 1989, the breeding population was estimated at about 

 261,400 breeding birds at 1 1 active colonies (i.e., 24% of the U. a. califomica population). The largest 

 colonies were at Castle Rock, False Klamath Rock, Green Rock, Flatiron Rock, and False Cape Rocks. 

 Colonies had lower numbers in 1993 indicating short-term abandonment during the severe 1992-93 El Nino, 

 but with few long-term detrimental effects. Recolonization and population increase have continued since the 

 1970s at the southern end of this population. 



The vast majority of murres in western North America, south of Alaska, now breed in Oregon. Numbers 

 of murres in the nineteenth and early twentieth centuries were much lower owing to extensive use of coastal 

 rocks and islands by native peoples, followed by egging and human disturbance by early settlers. However, 

 the population increased for several decades in mid-twentieth century. By 1 988, about 7 1 1 ,900 breeding birds 

 were estimated at 66 active colonies (i.e., 66% of the U. a. califomica population). The largest colonies were 

 at Shag Rock, Finley Rock, Middle Rock, Gull Rock (Cape Blanco), 270- 1 10, Cat and Kittens, and 219-018. 

 A sample of 15 colony sites indicated that murre numbers changed little from 1988 to 1995, except for 

 short-term abandonment during the severe 1992-93 El Nino. Long-term detrimental effects from severe El 

 Ninos in 1982-83 or 1992-93 have not been detected. 



Historical accounts indicate that murre populations in Washington increased from 1907 to 1979. In 1979, 

 about 53,000 breeding birds were estimated at 18 active colonies. The largest colonies were at Split Rock, 

 Willoughby Rock, Grenville Arch, and Rounded Island. Between 1979 and 1986. a 43.7% per annum 

 (P = 0.006) decline occurred in the number of murres attending breeding colonies in southern Washington. 

 Overall numbers of murres in Washington declined 13.3% per annum (P = 0.003) from 1979 to 1995. By 

 1988, about 7,000 breeding birds (i.e., less than 1% of the U. a. califomica population) remained. Declines 

 apparently were related to the 1981 warm water event, the 1982-83 El Nino, and anthropogenic factors (i.e., 

 human disturbance at colonies and gillnet and oil-spill related deaths). No recovery occurred in southern 

 Washington from 1984 to 1995 but limited increase in the number of murres attending some colonies in 

 northern Washington was documented. Increase at Tatoosh Island from 1984 to 1995 involved intercolony 

 movements and intrinsic growth. The Washington murre population size has recovered little since its decline 

 in the early 1980s, and remained low through 1995. 



