Female-female aggression explains polyterritoriality in male pied flycatchers

Abstract

Many male pied flycatchers, Ficedula hypoleuca, try to attract a second mate in a distant territory around the time their initial mate lays her clutch. In this study their success at becoming polygynous increased with the distance between the two territories. Two hypotheses may explain this result: either females are prevented from settling close to the male's initial nest because of aggression from the initial female (the female aggression hypothesis), or males can more easily hide their mating status and deceive females into polygyny the further apart the nests are (the deception hypothesis). These hypotheses were tested by presenting a female in a cage near a male's secondary nestbox during 3-h trials. (1) Females (and males) were able to locate and identify their mates a long distance from their own nests. (2) The male's initial mate often visited the male's secondary territory and (3) she was aggressive towards the caged female. (4) The proportion of initial mates visiting the male's secondary territory decreased with the distance from their own nests. (5) The initial mates spent less time in the male's secondary territory during their incubation periods than they did earlier on. (6) The already-mated males were more often absent from their secondary territories the further they were from their initial nests; this occurred despite the presence of the caged female. These results are most, consistent with the female aggression hypothesis.