Adult Survival of the Black Guillemot in Iceland

We studied adult survival of the Black Guillemot (Cepphus grylle) based on a capture-recapture data set collected in 1974-1995 in a colony in western Iceland. A total of 1,483 individuals were observed once or more as breeders; some of these were local or immigrant recruits. There was no evidence that adult survival varied over time; the estimated constant survival was 0.870 (95% confidence limits 0.855-0.884). This was similar to previous estimates for this species, but precision was very high. Because many guillemots drowned in fishing nets near our study site, we attempted to model survival as a function of local fishery effort; we were unable to do this because of excessive variation in capture effort. The final model also included a separate survival estimate for the first year after the first capture as breeder. This apparent first-year survival declined over time from 0.900 to 0.562. Both the lower apparent first-year survival and the negative trend were likely due to the presence of low-capturability individuals in the data set. We suggest that some birds were very difficult to capture because their nests were in shorebird or tern territories. The lower adult survival of Black Guillemots compared to other Atlantic alcids (murres, puffins) is presumably related to their inshore feeding habits, which also allow this species to raise two chicks to fledging.