Diet quality during pre-laying and nestling periods influences growth and survival of Florida scrub-jay (Aphelocoma coerulescens) chicks

Abstract

Food availability is one of the most important determinants of successful reproduction in birds. In a previous study, it was shown that Florida scrub-jays Aphelocoma coerulescens maintained a third egg mass when supplemented with a high fat and high protein diet during pre-breeding, as opposed to birds that were not supplemented that laid third eggs markedly lighter in mass than first- and second-laid eggs. Increases in egg quality promote chick growth and survival in many avian species. In this study, scrub-jays were provided with supplements throughout the pre-laying and nestling periods of 2001 and 2002 to investigate whether diet quality influenced growth and survival of chicks. Fledging success and survival to independence of unsupplemented chicks were higher for 2002 compared with 2001 indicating that breeding conditions (e.g. natural food availability) for jays were probably improved in the former year. Consistent growth patterns were found during the first 11 days post-hatch between chicks on supplemented and those on unsupplemented territories. Of the three growth measures, only seventh primary feather growth tended to be greater for third-hatched chicks on supplemented territories compared with third-hatched chicks on control territories. Food supplementation influenced survival of chicks. Compared with chicks hatching on unsupplemented territories, fledging success of chicks hatching from second-laid eggs was significantly greater in 2001, but not in 2002. Chicks from third-laid eggs on supplemented territories also tended to survive better in 2001 compared with chicks from unsupplemented territories, but, again, no such effect was found in 2002. We conclude that food supplementation in the pre-laying and nestling periods results in little measurable improvement in chick growth. However, improvements were found in survival of chicks that may be mediated through improvements in egg quality, but also may be the result of changes in foraging strategies of provisioning birds on supplemented territories. Chicks on supplemented territories might be in better body condition than those on unsupplemented ones. Methods other than morphometrics may be required to detect elevations in body condition of chicks raised on supplemented territories.