Disappearance of female pied flycatchers in relation to breeding stage and experimentally induced molt

According to life history theory, adult mortality during the breeding season may have an important influence on the evolution of several aspects of breeding ecology in birds, yet few studies have tried to quantify such mortality. We studied disappearance of Pied Flycatchers (Ficedula hypoleuca) during four breeding seasons in a woodland area in Norway provided with nest boxes. The main cause of disappearance was probably predation by the European Sparrowhawk (Accipiter nisus). Disappearance was nonsignificantly higher in females (10% per season, n = 305) than in males (7% per season, n = 269). Female disappearance peaked during egg-laying (0.53% per day), but was also high during the nest-building (0.42% per day) and nestling (0.36% per day) stages. It was low during incubation (0.05% per day), probably because less time was spent outside the nest. Low risk of predation during incubation may help to explain why female body mass remains high during this stage of breeding but drops soon after hatching. Females with selected flight feathers experimentally removed to simulate molt suffered a much higher disappearance per season (24%, n = 109) than did control females (10%, n = 305). This may help to explain why breeding and molt usually are temporally segregated activities in birds. Variation in female body mass and size (wing length, tarsus length), age, previous breeding experience, mating date, laying date, clutch size, and mating status could not account for the variation found in female disappearance. Disappearance was lower in males than in females during the nest-building period, despite the more conspicuous plumage color of males. This may be explained by the fact that only the female builds the nest. We suggest that risk of predation is an important constraint on sexual selection of male plumage color in species in which males take part in nest building. Key words: adult predation; body mass; Ficedula hypoleuca; molt; physiological stress; sexual dimorphism.
INTRODUCTION In birds, one or both of the parents may sometimes disappear from an apparently successful nesting attempt. This may be for several reasons. For instance, they may desert the [...]