Offspring provisioning rates in an urban passerine : do they change with parental age?

Abstract

Studies have shown that offspring provisioning is one of the most demanding of parental activities in terms of both time and energy. European starlings (<i>Sturnus vulgaris</i>) are a socially monogamous yet facultatively polygynous passerine species. They exhibit biparental care in which both parents incubate the eggs and provision the offspring. Adult European starlings return to the study site to breed every year, making them an ideal species to examine the relationship between parental age and offspring provisioning rates. They have hackle (throat) feathers whose iridescent length allows classification of adults into one of two age categories 1) second year (SY, first-time breeders), or 2) after second year (ASY). The objective of my study was to examine offspring provisioning rates by both male and female parents who have been observed over at least two years. I predicted that adult males and females would provision their offspring at a higher rate than they did when they were younger (in the prior year). In support of my predictions, ASY males tended to provision the brood at a higher rate on days 7 or 8 of the nestling period. However, ASY males on day 13 or 14 of the nestling period tended to have a lower provisioning rate (provisions/hr/nestling) than when they were a year younger. I found no significant differences between the provisioning rates of ASY females on days 7 or 8 and 13 or 14 of the nestling period, which did not support my predictions. There were no significant differences in the number of provisions/nestling/hr made by SY or ASY males or females on day 7 or 8 of the nestling period. Understanding whether parental investment changes with parental age and how this might affect the reproductive success of European starlings is important in aiding the global population decline in avian species.