The Conflict Between Male Polygamy and Female Monogamy: The Case of the Pied Flycatcher Ficedula hypoleuca

Abstract

Some males of the pied flycatcher enhance their individual fitness by mating with 2 females, one of which receives their full support in caring for the brood, while the other is given very little or no aid and therefore, on average, produces a much reduced brood. These so-called secondary females have a low fitness. The theories of differential territory quality and of sexy sons to explain the bigamous strategy in this species and which argue that the male cheats some females into the role of being secondary are refuted. The trick used by the male is maintaining 2 spatially separate territories (polyterritorialism). Secondary females lay fewer eggs and take this as evidence that, at some point, they become aware of their true marital status and then, adaptively, reduce their clutch size. The alternative explanation that secondary females are intrinsically low-productive, for example, because of relatively younger age, can probably be refuted. Large males were overrepresented among the bigamists. Male fitness is relatively variable under the mating system of the pied flycatcher; this encourages strong sex dimorphism.