Allocation of parental investment by polygynous Pied Flycatcher males

Abstrakti

The parental roles in the feeding of nestlings were studied in the polygynous Pied Flycatcher Ficedula hypoleuca, with special emphasis on how the males allocated their investment between their broods. The study was carried out near Oslo, southern Norway, mainly during 1985 and 1986 . In general, primary females received more male assistance in raising their young than did secondary (including tertiary) ones, but there was a considerable variation in the investment pattern of individual males. This variation was apparently related to two main factors. First, maleassistance at secondary nests was less frequent in one of the study years (1985) with unfavourable weather conditions . Second, the males invested more heavily in their secondary broods when the hatching interval between the primary and the secondary broods was short . Consequently, the body weight of primary broods on day 13 increased with increasing degree of breeding asynchrony between the broods, whereas the body weight of secondary broods declined. There was also a tendency of reduced male assistance at the secondary nest when it was located far from the primary nest. The variation in male investment pattern could not be explained by any differences in brood size, nutritional condition of the young, or body reserves of the females ofthe two respective nests. The results are discussed in light of the polyterritorial breeding system of this species . We suggest that competition for maleparental investment is the reason why mated females are aggressive towards female intruders and that males show long-distance polyterritoriality in order to reduce the likelihood of female-female interactions, thereby increasing their chances of obtaining a secondary mate .