Meeting Abstract

44.2  Sunday, Jan. 5 10:45  Individual variation in provisioning effort does not result in larger offspring at fledging FOWLER, MA*; WILLIAMS, TD; Simon Fraser University; Simon Fraser University melinda.a.f@gmail.com

Parents that work harder at raising young should obtain fitness benefits but, theoretically, these benefits should come at some ‘cost of reproduction’. However, the predicted positive relationship between workload and fitness, in terms of chick quality, appears to be surprisingly poorly supported in the literature. We analyzed 7 years of provisioning (nest visit rate) and breeding success data in European starlings (Sturnus vulgaris) to investigate the causes and consequences of individual variation in parental care. Provisioning rate was extremely variable among individuals; when controlling for brood size, it varied up to 16 fold. Provisioning rate was negatively related to daily temperature, but was not impacted by rainfall. Mean fledgling mass was equal across brood sizes and independent of the presence of male provisioning effort. Total provisioning rate (at day 6-8) predicted fledging mass at day 17, but when assessed as provisioning per chick there was no effect on fledging mass. Individual birds appear to adjust workload to the number of chicks in the brood. However, there is large residual variation in provisioning which is independent of offspring quality (17 day mass) i.e. variation in provisioning per chick does not provide a payoff in the form of heavier chicks. This disconnect suggests either that : a) provisioning rate is not a good proxy for ‘work’ effort; or b) working harder to provision chicks does not have an immediate cost; or c) individuals do not bear the costs of work equally. Increased provisioning rate may not be reflective of increased work load in individuals that forage more efficiently. Alternatively, individual quality in exercise ability may explain some of the variation in provisioning rate.