Monitoring Nesting Seabirds: Reply to a Commentary by Ian C. T. Nisbet

Johnson and Krohn (2001) addressed the importance of timing when conducting surveys, and the effect of this variable on the ability of a monitoring program to statistically detect trends in numbers of breeding seabirds. However, Nisbet's commentary on our paper concentrates in general on the use of counts based on aerial photographs as a reliable survey measure, and on the precision and accuracy of gull counts that were conducted as part of our study. While comparisons of different survey techniques and associated accuracy assessments are important, this was not the subject of our paper. Our focus was on the temporal variability in numbers of nesting Double-crested Cormorants (Phalocrocorax auritus), Great Blackbacked Gulls (Larus marinus) and Herring Gulls (Larus argentatus) in coastal Maine across the breeding season, and the potential effect that survey protocols (e.g., conducting surveys at different times of year, for different survey windows or for different island sample sizes) could have on the ability of a survey program to detect long-term population trends.