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Short-Lived Repeatabilities in Long-Lived Great Skuas: Implications for the Study of Individual Quality

P. Catry, G. D. Ruxton, N. Ratcliffe, K. C. Hamer and R. W. Furness
Oikos
Vol. 84, No. 3 (Mar., 1999), pp. 473-479
Published by: Wiley on behalf of Nordic Society Oikos
DOI: 10.2307/3546426
Stable URL: http://www.jstor.org/stable/3546426
Page Count: 7
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Short-Lived Repeatabilities in Long-Lived Great Skuas: Implications for the Study of Individual Quality
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Abstract

Excluding age and experience effects, individual quality is frequently assumed to be a fixed trait. This paper tests whether an individual's apparent quality, as indicated by its timing of breeding, is indeed permanent. This is assessed by studying the repeatability of laying dates of a long-lived seabird, the great skua Catharacta skua. Laying date is known to be an important component of fitness in many seabirds, including great skuas. Mathematical models were constructed to evaluate the effect of age-specific timing of breeding on repeatability estimates. Simulations show that, in short-term studies (lasting 2 or 3 years), age-specific laying dates can produce spurious repeatabilities with values ranging between 0.1 and 0.2, when the value should be zero. Field observations showed that individual consistency of timing of breeding was high over short time intervals, but disappeared over longer periods (4 or 5 years). A comparison between field data and the simulations demonstrated that the observed high repeatabilities in consecutive years, and the fast subsequent declines, cannot be fully accounted for by age effects. The mechanisms underlying this surprising pattern are completely unknown, but results clearly suggest that apparent individual quality is a transient attribute in these birds.

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