BIOLOGY AND CONSERVATION OF THE COMMON MURRE 89 



the k t correction factor is calculated using the formula 

 jfc f (lj) = fi e (2 V/i t (/, ) where n f = number of plot sites where 

 an egg was laid that season, which is then multiplied by 

 two breeding birds/site, and n ; = the number of murres 

 counted at time t. This calculation differs slightly from 

 it as described by Birkhead and Nettleship ( 1 980), which 

 calculates number of breeding pairs. Alternatively, a , 

 correction factor also has been used where n e equals the 

 number of egg-laying sites on the survey day (Takekawa 

 et al. 1990). Whereas little difference exists between 

 these versions of k at the South Farallon Islands 

 (Sydeman et al. 1997), the k, calculation is preferred 

 overall because it prevents possible biases relative to 

 the timing of the survey. Annual k values can be 

 determined by averaging counts from different days. 



Since 1979. various k ; and , values have been 

 used to adjust whole-colony counts to estimate the 

 number of breeding adults at colonies, which then can 

 be summed to estimate the breeding population in 

 California. A general k correction factor of 1 .67 was 

 used to adjust whole-colony counts in 1979-82 (Sowls 

 et al. 1980; Briggs et al. 1983) based on data from the 

 South Farallon Islands in the early 1970s (Ainley 1976, 

 and personal communication). Takekawa et al. (1990) 

 calculated an average k^ value of 1.68 by averaging 

 four years of data from 1980 to 1986. This average value 

 was applied to all colonies since 1980. except at the 

 South and North Farallon Islands where annual values 

 were applied. Carter et al. (1992) also used this A:, value 

 of 1.68 to estimate colony size at all colonies in 1989. 

 except at the Farallon Islands where an annual 1989 

 value was used. More details about k correction factors 

 developed at the South Farallon Islands are available 



elsewhere (Boekelheide et al. 1990; Takekawa et al. 

 1990; Carter et al. 1992). Sydeman et al. (1997) 

 reevaluated and corrected all data from 1985 to 1995 

 and calculated k } values that averaged 1.67 with 

 relatively little variation among years. Takekawa et al. 

 (1990) reported the general accuracy of estimates of 

 breeding adults at colonies in California to be within 

 10%. However, further work is required to better 

 determine error associated with these estimates. 



Oregon 



Murre colonies in Oregon were censused from 1966 

 to 1975 by USFWS biologists using fixed- wing aircraft. 

 These aerial censuses were generally flown in late June 

 or early July and relied on visual estimation, rather than 

 aerial photography, to determine the number of murres 

 present. This method often resulted in underestimation, 

 especially at larger colonies; 197475 estimates of 

 colony size were probably low. Aerial photographic 

 surveys were first used in 1979 during the first coastwide 

 survey of nesting seabirds in Oregon (Varoujean and 

 Pitman 1980). However, many of the photographs were 

 taken too late in the season to provide accurate counts 

 and the population estimate was low. 



In late June 1989. Ecological Consulting 

 Incorporated conducted murre colony counts in Oregon 

 (Briggs et al. 1992). The focus of their research was to 

 conduct offshore and coastal strip transects surveys of 

 marine mammals and seabirds using a fixed-wing 

 aircraft On June 27 and 28, they made a nonstandardized 

 aerial survey of murre colonies and counted murres at 

 coastal locations using visual estimates from aircraft 



Figure A-2. Aerial photographs 

 were projected onto a wall with 

 white sheets of paper, best 

 photographs were selected for 

 counting, and then each murre 

 was marked on the paper. In this 

 photo, the best close-up 

 photographs of Tillamook Rock, 

 Oregon, have been pieced 

 together, and murres on different 

 parts of the rock are being marked 

 (Photo by D. S. Pitkin). 



