Reproductive success of monogamous and polygynous pied flycatchers (Ficedula hypoleuca)

One of the most interesting aspects of the mating system of pied flycatcher s is the regular occurrence of polygyny. Here we present data on the reprod uctive success of polygynously paired pied flycatcher males compared to mon ogamous males based on paternity analyses through DNA fingerprinting. Males paired with two females suffered a higher loss in reproductive output per female compared to monogamous males due to (1) a greater proportion of unha tched eggs in their broods, (2) greater nestling mortality and (3) a greate r probability of being cuckolded. Nevertheless, the number of fledglings wa s significantly greater for polygynous males. Based on the number of nestli ngs that returned for subsequent breeding seasons, however, the reproductiv e success of monogamous and polygynous males did not differ significantly. These data raise the question as to why males attempt polygyny.