Nest positioning by male Daito White-eyes Zosterops japonicus daitoensis improves with age to reduce nest predation risk

Abstract

Age-related improvement in reproductive success is widely observed in birds, and the mechanisms by which productivity is enhanced have received considerable attention. However, little is known about how parental age affects the loss of eggs or nestlings despite the fact that age effects on nesting success are often reported. We examined parental age effects on reproductive success in relation to the avoidance of nest predation in an island subspecies of the Japanese White-eye, the Daito White-eye Zosterops japonicus daitoensis. Clutch size and annual number of breeding attempts did not differ between parental age classes. Reproductive success was affected only by male age through an increase in nesting success. Nest failure was attributed only to predation in this species and nest concealment and nest height were important nest characteristics promoting successful fledging. Older males built their nests in more concealed and higher positions than first-year birds, regardless of vegetation status around the nest. Analysis of individual birds suggested that by shifting the nest to a safer position, male White-eyes achieved higher nesting success than in the previous year. Of three hypotheses of age-related improvement in reproductive success considered, our data favoured the hypothesis that as individuals grow older, their breeding competence improves. © 2012 The Authors. Ibis © 2012 British Ornithologists' Union.