Female Choice and the Causes and Adaptiveness of Polygyny in Great Reed Warblers

Abstract

(1) In a dense reedbed at Lake Biwa in Japan 30-80% of male great reed warblers were polygynous each year, whereas others remained monogamous or even unmated throughout the breeding season. (2) Males that had established territories by mid-May (early males) were more likely to be polygynous than those that established territories after mid-May (late males). Second females were attracted to the territories of early males, even though unmated late males held territories nearby. (3) Many late males attracted mates when all the first mates of early males either had not yet laid or had chicks. At these stages, males do not sing actively and hence did not attract females. Already mated early males attracted as many or more females as unmated late males as long as they were singing. (4) Early males held large territories early in the breeding season and late males established their territories by carving out a part of the former's territory. Territories of early males always included an area of dense vegetation which was never yielded to later arrivals.