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Population Dynamics of Common Guillemots Uria aalge on Skomer Island, Wales

B. J. Hatchwell and T. R. Birkhead
Ornis Scandinavica (Scandinavian Journal of Ornithology)
Vol. 22, No. 1 (Jan. - Mar., 1991), pp. 55-59
Published by: Wiley on behalf of Nordic Society Oikos
DOI: 10.2307/3676621
Stable URL: http://www.jstor.org/stable/3676621
Page Count: 5
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Population Dynamics of Common Guillemots Uria aalge on Skomer Island, Wales
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Abstract

The Common Guillemot population on Skomer Island, Wales, has recently increased following a long period of decline. We measured population parameters in 1985-89 and compared them with parameters measured in 1973-75 to identify the processes responsible for these population changes. Productivity increased significantly from $0.72\ \text{chicks pair}^{-1}\ {\rm yr}^{-1}$ in 1973-75 to $0.79\ \text{chicks pair}^{-1}\ {\rm yr}^{-1}$ in 1986-87. Adult survival was higher in 1986-89 (94.0%) than in 1973-75 (91.5%), but the difference was not significant. Information is not yet available to determine whether survival to breeding age, and therefore recruitment, has also increased. A model of population growth is presented, incorporating observed changes in productivity and adult survival, and employing three values for survival to breeding. A close fit to observed population changes was obtained with a survival rate to first breeding at five years of 41.1%, the highest survival rate previously recorded for Common Guillemots.

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