Seabird Abstracts

Recruitment to a seabird population depends on

environmental factors and on population size

Crespin L, Harris MP, Lebreton J-D, Frederiksen M & Wanless S (2006) J Animal Ecol 75:228-238

1. A novel capture-mark-recapture (CMR) method was used to build a multistage model of recruitment by young birds to a breeding population of Common Guillemots Uria aalge on the Isle of May, Scotland. Recruitment of a total of 2757 individually marked guillemots over 17 years was modelled as a process where individuals had to move from an unobservable state at sea, through a non-breeding state present in the colony, to the breeding state. The probabilities of individuals returning to the colony in a given year, at age 2 and 3-4 years, were positively correlated with an environmental covariate, the winter North Atlantic Oscillation index (WNAO) in the previous years.

2. For 2 year olds, there was a negative relationship with breeding population size, suggesting that density dependence operated in this colony through limitation of food or some other resource.

3. Survival over the first 2 years of life varied with cohort, but was unrelated to the WNAO. Mean survival over this 2-year period was high at 0.576 (95% CI: 0.444; 0.708).

4. This high survival, combined with a low ‘local’ survival after age 5 years of 0.695 (0.654; 0.733) and observations of the Isle of May chicks at other colonies, suggests that most surviving chicks return to the natal colony before deciding whether to recruit there or move elsewhere.

Keywords: capture–mark–recapture, common guillemot, density dependence, North Atlantic Oscillation, recruitment


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