Seabird Abstracts

Within- and between-year variation in the

juvenile survival of Common Guillemots Uria aalge

Harris MP, Frederiksen M & Wanless S (2007) Ibis 149:472-481

We studied juvenile survival of 20 cohorts of Common Guillemots Uria aalge chicks colour-ringed on the Isle of May, Scotland, using both live observations at the colony and dead recoveries, allowing an estimation of fidelity of the colony as well as survival. In this seabird, chicks leave the colony when only partly grown and are cared for by the male parent for several week afterwards. First-year survival varied strongly between cohorts, with a mean of 56% (range 30% - 91%). We did not identify any covariates which could explain this variation, whether relating to climate, population size or prey density. Survival was low during two regime shift episodes in the North Sea (1987-1990 and 2000 onwards). Early hatched chicks were substantially more likely to survive than those hatching later in most years, whereas body condition at ringing had no detectable effect. Ringing recoveries indicated that mortality was highest in mid-winter, i.e. well after the cessation of paternal care. These results do not support the hypothesis that variation in prey quantity or energy content before fledging is a primary driver of variation in juvenile survival. Rather, it seems that chicks of high-quality parents are more likely to survive, as high-quality females tend to lay earlier in the season, and high-quality males presumably are better able to prepare their chicks to survive their first winter at sea. Very few (4%) Guillemots emigrated permanently before age 3, but from age 5 onwards 25-30% of the birds annually left the colony or otherwise became unobservable.

Keywords: none


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