Body size and age of recruitment in Snow Geese Anser c. caerulescens

Abstract

'At what age to start breeding?' is a question fundamental to analysis of life histories. VVhile there has been considerable interest in the theoretical aspects of age of first breeding, comparatively little work has been done on the problems of estimating recruitment rates in wild populations. Most studies to date have relied on ad hoc methods that rely on one or more assumptions which may be generally untenable. Recently, it has been suggested that mark-recapture analysis can provide a robust, statistically formal approach for the analysis of recruitment, by using 'reverse capture-histories' to estimate the probability of entering the population over a given interval. We applied this approach to data from the arctic-breeding Lesser Snow Goose Anser c. caerulescens¸, using data from a long-term study in subarctic Canada. We tested the hypothesis that recruitment rate in this species was influenced by structural size. Since arcticnesting geese rely heavily on endogenous nutrient reserves for reproduction, structurally smaller birds may be less able to recruit at a young age than larger birds. However, despite significant long-term changes in body size, and significant annual variation in recruitment rate, we found no evidence of correspondence between the two.