Manipulations of male parental investment in polygynous pied flycatchers, Ficedula hypoleuca

We designed three experiments to identify important cues as to how bigamous male pied flycatchers (Ficedula hypoleuca) apportion nestling feeding between their broods. Normally, males give priority to their primary brood, that is, the brood of their first-acquired mate. In the first experiment, we reversed the hatching order of primary and secondary broods by substituting eggs. Males responded by reallocating their efforts in favor of secondary broods. Males thus favored the brood that hatched first, irrespective of female mating order. In the second experiment, carried out on the same males when the younger brood was 4 or 5 days old, we transferred the older brood to the nest of the younger, and vice versa; the males changed their investment pattern accordingly, still giving priority to the older brood. In the third experiment, primary and secondary broods were made to hatch on the same day. In these cases, males divided their nestling feeding efforts fairly equally between the broods. The results reveal a remarkable flexibility of male investment decisions, which is discussed in light of parental investment theory. The fact that the degree of male assistance to secondary mates is variable and that it is to a large extent predictable from the nest initiation asynchrony of the two females has important implications for our understanding of the polyterritorial mating system of this species. [Behav Ecol 1990;1:48-54]