Age-specific reproductive performance in red-billed choughs Pyrrhocorax pyrrhocorax: patterns and processes in a natural population

Using data from a 20-year study of individually marked red-billed choughs, we examine how reproductive performance varies with age in male and female breeders, and investigate whether population-level trends result from changes in individual performance and/or the phenotypic composition of the breeding population. Across the population, mean clutch size, the probability of breeding successfully and the number of offspring fledged during successful attempts increased and then declined with female age. Male age did not explain a significant proportion of the residual variation. All three measures of reproductive performance improved and then declined with age within individual females. Females that died young laid relatively small clutches and fledged few offspring before death. Thus mean performance improved across young age classes partly because some poor breeders were absent from older age classes. Females that ultimately reached the greatest ages had laid small clutches and fledged few offspring during their first few breeding attempts. Females that were more productive when they were young had relatively shorter lives. These data indicate a trade-off between early reproduction and future survival in choughs, and suggest that individuals that reach old age are phenotypically distinct from an early stage in their breeding lives.

M. Reid, E. M. Bignal, S. Bignal, D. I. McCracken and P. Monaghan, Journal of Animal Ecology 72 (5), 765-776