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Population Parameters for the Common Guillemot Uria aalge
T. R. Birkhead and P. J. Hudson
Ornis Scandinavica (Scandinavian Journal of Ornithology)
Vol. 8, No. 2 (Nov. 15, 1977), pp. 145-154
Stable URL: http://www.jstor.org/stable/3676099
Page Count: 10
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A number of population parameters for the Common Guillemot are presented, derived from a study of marked birds on Skomer Island, Wales, and from recoveries of ringed birds. Breeding success on Skomer averaged 0.7 chicks/pair, and in two years adult survival averaged 91.5%. Guillemots returned to Skomer in their second year, and prior to breeding birds congregated in clubs. Guillemots first bred at four years old, but most of them probably breed for the first time in their fifth year. Two different estimates for the survival rate of birds up to five years old were: 16% and 20%. Juvenile survival calculated from ringing recoveries varied from 27% for southern England, where numbers are stable or decreasing, to 41% in north-east Canada, where numbers have increased. Between 1972 and 1977 the Skomer Guillemot population remained at a similar level. If adult survival is 91.5% and 100 pairs of Guillemots produce 70 chicks, 17 (24%) of these must survive to breeding age to maintain a stable population. Factors influencing population size are discussed.
Ornis Scandinavica (Scandinavian Journal of Ornithology) © 1977 Nordic Society Oikos