The use of k values to convert counts of individual razorbills Alca torda to breeding pairs

A 32-year study of Razorbills Alca torda on the Isle of May, southeast Scotland,showed that the mean value of k, used to convert counts of individual birds to breeding pairs, averaged 0.795 ± 0.019 SE and increased ignificantly over the period. This value was much higher than the 0.67 used to convert counts of birds during censuses of colonies for Britain and Ireland in both 1985–88 and 1998–2002. Assuming that the average values recorded at the Isle of May at the time (0.767 and 0.851, respectively) were representative of other colonies, the total British and Irish populations would have been 14% and 27%, respectively higher than the published totals. Given plans for another nationwide survey in the next few years it would be useful to obtain k values from additional colonies to provide better assessment of changes in breeding numbers.