BIOLOGY AND CONSERVATION OF THE COMMON MURRE 65 



Current Population Size and Distribution of 

 Breeding Colonies in British Columbia 



In British Columbia, murres now breed almost 

 entirely at Triangle Island (Table 2.7), and breeding no 

 longer occurs at four of five other known colonies 

 (Rodway 1991). Murres have not bred recently at 

 Cleland Island, Florencia Island, or Starlight Reef in 

 1982, 1984, and since 1990 (Rodway and Lemon 1990; 

 BCNRS; A. Dorst, personal communication). At Sartine 

 Island, no murres attended cliffs in 1987 and 1989. but 

 440 and 113 murres were observed in nearby waters 

 (Rodway et al. 1990b). At the Kerouard Islands, the 

 highest numbers (400 murres) were counted on cliffs in 

 1987 (Rodway et al. 1990a). Annual records kept by 

 tour-boat operators indicated intermittent attendance 

 of small numbers of birds from 1989 to 1991, and 1994 

 to 1996 (200 murres in 1995), but none were observed 

 in 1 992-93 or 1 997 (R. W. Campbell, unpublished data). 

 On occasion, murres also have been noted on land at 

 other locations wherein no breeding occurred on 2 

 July 1974, five murres in breeding plumage were 

 observed in intertidal habitats at Vivian Island and on 7 

 July 1974, two murres were noted on a breakwater off 

 the jetty at the Tsawassen ferry terminal (R. W. 

 Campbell, unpublished data). 



Triangle Island was examined extensively from 

 1980 to 1985 (Vallee and Cannings 1983; Vallee and 

 Carter 1987; Rodway 1990: Rodway et al. 1990b). 

 During this period, murres bred in four main areas: Puffin 

 Rock, Murre Rock, Castle Rock, and Southeast Point 

 (Rodway 1990). On 10 July 1982, a partial count of 

 4,910 murres was obtained at the main colony on Puffin 

 Rock. In 1984, about 12,000 murres were estimated on 

 the water in early July, but all breeding attempts failed 

 (see below) and only small numbers were present on the 

 breeding slopes. In 1985, murres bred successfully, and 

 3,956 murres were counted in different breeding areas 

 between 9 and 19 July. 



The most complete estimate of colony size for 

 Triangle Island was made in 1989 (Rodway 1990). An 

 average of 5,839 murres (range, 3,335-6,144) was 

 derived from replicated counts of murres from boat 

 photographs between 27 July and 17 August 1989. 

 Numbers from four complete counts (between 1 800 and 



2000 h [PDT] when daily attendance was highest) ranged 

 from 5,846 to 6.144 birds. To determine a total number 

 of birds attending the colony, the 5,839 mean count 

 was adjusted with a "ground-truthing" or "g" correction 

 factor of 1 .44. This correction factor was determined by 

 averaging the difference between telescope and photo 

 counts over the 0700-2100 period. Thus, 8,408 birds 

 were estimated to attend photographed areas. An average 

 of 1.535 murres in other areas (i.e., not photographed) 

 were added to obtain a total of 9,943 birds. To derive an 

 estimate of the number of breeding adults at the colony, 

 a k correction factor of 0.82 was applied to derive 8, 1 53 

 breeding birds or 4,077 breeding pairs. This estimate 

 was higher than previous estimates due mainly to more 

 complete coverage of the colony. A repeat of the survey 

 using similar methodology in 1996 probably 

 underestimated total numbers because some chicks and 

 adults had departed from the colony before the count 

 was completed (Parrish 1997). 



By adding recent complete counts of murres at 

 Triangle Island and the Kerouard Islands, we obtained a 

 total of 10,296 birds which corresponded to a total 

 breeding population estimate for British Columbia of 

 about 8,300 breeding birds (Table 2.7). 



Population Trends in British Columbia 



Historical records and recent data were inadequate 

 to determine population trends in British Columbia. 

 Colonization and abandonment of colonies along the 

 west coast of Vancouver Island in the late 1960s and 

 1970s are difficult to interpret and may indicate an 

 intermittent colonization event, perhaps during a period 

 of colony growth at Triangle Island and colonies in 

 Washington. 



Replicated counts at three subcolony sites on 

 Triangle Island in 1982, 1985, and 1989 were highest 

 in 1982 and lowest in 1985 (Table 2.8; Rodway 1990). 

 Counts were conducted at different times in the 3 years, 

 but decrease between 1982 and 1985 and limited 

 increase between 1 985 and 1 989 were similar to trends 

 at certain northern Washington colony complexes (see 

 Washington section). No murres bred successfully at 

 Triangle Island in 1984 when complete breeding failure 

 of murres and most other surface-breeding species 

 occurred because of severe weather and prey shortage 



Table 2.8. Comparison of counts of common murres at subcolony sites on Triangle Island 

 in 3 years from 1 982 to 1 989 (from Rodway 1 990). 



Location 



Site number 



1982 



1985 



1389 



