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 asp ects of breeding ecology in birds, yet few studies have tried to quant ify such mortality. We studied disappearance of Pied Flycatchers (Fice dula hypoleuca) during four breeding seasons in a woodland area in Nor way provided with nest boxes. The main cause of disappearance was prob ably predation by the European Sparrowhawk (Accipiter nisus). Disappea rance was nonsignificantly higher in females (10% per season, n = 305) than in males (7% per season, n = 269). Female disappearance peaked d uring egg-laying (0.53% per day), but was also high during the nest-bu ilding (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 spe nt outside the nest. Low risk of predation during incubation may help to explain why female body mass remains high during this stage of bree ding but drops soon after hatching. Females with selected flight feath ers experimentally removed to simulate molt suffered a much higher dis appearance per season (24%, n = 109) than did control females (10%, n = 305). This may help to explain why breeding and molt usually are tem porally segregated activities in birds. Variation in female body mass and size (wing length, tarsus length), age, previous breeding experien ce, mating date, laying date, clutch size, and mating status could not account for the variation found in female disappearance. Disappearanc e was lower in males than in females during the nest-building period, despite the more conspicuous plumage color of males. This may be expla ined by the fact that only the female builds the nest. We suggest that risk of predation is an important constraint on sexual selection of m ale plumage color in species in which males take part in nest building .