Staffan Bensch , Dennis Hasselquist Molecular Population Biology , Department of Ecology , Lund University , Sweden. The great reed warbler Acrocephalus arundinaceus breeds in highly productive lakes and reed marshes over a large part of the Palaearctic temperate region. It is a long distance migrant that spends the winter in tropical Africa. The population of great reed warblers at Lake Kvismaren has been studied since 1983 whereafter almost all males, females and nestlings have been ringed. The frequency of polygyny in great reed warblers is one of the highest among European passerines.
Males arrive to the breeding area about two weeks before the females.
In an experiment with females tagged with radiotransmitters , we found that they visit the territories of three to twelve males before choosing a breeding partner . Females that choose to breed with already mated males enjoy similar fledging and recruitment success as females that choose to breed with unmated males, and this supports the view that the polygyny threshold model can explain this polygynous mating system. The fitness gain seems to be increased survival of young to adulthood as male song repertoire size correlates with the relative post-fledging survival of offspring. Females engaging in extra-pair copulations obtain no direct benefits from the cuckolderer. This suggests that good singers are attractive because they carry genes that promote fledgling survival.