RISK-TAKING DURING PARENTAL CARE - A TEST OF 3 HYPOTHESES APPLIED TO THE PIED FLYCATCHER

According to life-history theory, there will often be a conflict betwe en investment in current versus future reproduction. If a predator app ears during breeding, parents must make a compromise between ensuing t he growth and survival of offspring (nest defence, feeding and broodin g of young), and reducing the risk of predation to ensure their own su rvival. We model three hypotheses for the outcome of this conflict whi ch are particularly relevant for altricial birds. They are not mutuall y exclusive, but focus on different costs and benefits. (1) Parental i nvestment is determined by the parents' own risk of predation. This hy pothesis predicts that a lone parent should take smaller risks than a parent that has a mate. (2) Parental investment is related to the repr oductive value of the offspring: Parents are predicted to take greater risks for larger broods, larger-sized or older offspring. (3) Finally , we present the new hypothesis that parental investment is related to the harm that offspring would suffer during a period of no parental c are (incubation, brooding, feeding). This hypothesis predicts that par ents should take greater risks for younger offspring, or for offspring in poorer condition, because the marginal benefit of parental care is largest in such cases. Hence, one may also expect that lone parents s hould take greater risks than two parents because their offspring are more in need of care. We tested these hypotheses on the pied flycatche r (Ficedula hypoleuca) by presenting a stuffed predator of the parents (a sparrowhawk, Accipiter nisus) close to the nest when parents were feeding the young. Risk taking was measured as the time that elapsed u ntil the first visit to the nest. Most support was found for the ''har m to offspring'' hypothesis. Previous studies have usually measured th e intensity of nest defence against typical nest predators, and have f ound evidence for the ''reproductive value of offspring'' hypothesis. However, our model predicts that the importance of the reproductive va lue of the offspring should decrease relative to the harm that offspri ng would suffer if they were not cared for when the predator type chan ges from a nest predator to a predator of adults, and when conditions for breeding turn from good to bad.