Diet or exercise? How do birds cope with transitions in workload associated with parental care or fledging?

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Exercise can be defined as physical activity involving movement supported by sustained locomotor performance, cardiovascular adaptations, and increases in energy expenditure above basal levels. Such a broad definition can theoretically be applied to many routine activities in free-living animals, e.g. foraging, escaping predators, finding mates, providing parental care. These activities are essential for reproduction and survival, and costs of under-performing' are a matter of life and death for free-living animals unlike human athletes at the Olympics. However, it's unclear if concepts such as “exercise” and “training” apply to free-living animals? Do natural populations harbour “couch potatoes” and athletes? Do free-living animals “train” to improve their performance in fitness-related activities (e.g. feeding chicks) and how do animals prepare for, and deal with, rapid transitions in workload or locomotor performance (i.e. “getting up off the couch”)?In a free-living population of European starlings (Sturnus vulgaris) we focus on two phases of breeding that involve natural, abrupt changes in “workload”: a) from incubation (relatively sedentary) to chick-rearing (highly active) in adult females, and b) from enforced inactivity as nestlings to sustained flight at fledging in young birds. Research will integrate life-history, ecology, behaviour and physiology. In adults, we will directly manipulate costs of workload (using wing-clipping) or the benefit of workload (using egg removal to delay hatching and, thus, reproductive value' of investing in chicks). We will monitor activity of all females 24/7 using an automated radio tracking, obtain detailed information on foraging behaviour using accelerometers, night-vision and video cameras, and combine this with comprehensive physiological analysis (a suite of 15 physiological traits). We will test the hypotheses that female parents use a relatively simple physiological adaptation (mass loss) to adjust to varying workload demands, i.e. they “diet”. We will also explore the significance of novel' aspects of behaviour associated with parental care (e.g. nocturnal activity). Are these important behaviours allowing foraging for self-maintenance, or perhaps even opportunities for “exercise” allowing birds to get in shape ready for chick-rearing? In chicks, we will directly manipulate development (e.g. using hormonal treatment) to test the hypothesis that individual variation in growth rate is constrained by physiological mechanisms and that physiological maturity at fledging (not somatic maturity) is the main determinant of post-fledging behaviour, flight ability and survival. In addition, we will test the idea that chicks use “push-ups” as a form of pre-fledging exercise to assess their body mass and determine their required pre-fledging mass recession to optimise flight ability after fledging.