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Abstract

Many models proposed to explain the occurrence of polygyny in birds implicitly assume that females actively choose males offering the highest quality breeding situations. However, strong evidence of active mate choice by females in polygynous bird species is scarce. This study asked whether females in a polygynous population of house wrens Troglodytes aedon, a small, cavity-nesting songbird, base their choice of a mate at least partly on characteristics of the nest site that he controls. Already-mated males were randomly assigned one of two types of nest boxes to which they could attempt to attract secondary mates. Some males were given standard-type boxes with small entrance holes in the front sides of boxes, while other males were given boxes with larger entrance holes located in the boxes' roofs. A preliminary experiment revealed that female house wrens overwhelmingly prefer front-entrance to roof-entrance boxes when both types of boxes are available on the same territory. Females chose mated males with front-entrance boxes over mated males with roof-entrance boxes significantly more often than expected by chance. This preference demonstrates that female house wrens do discriminate among potential mates and base their choice of a mate at least partly on characteristics of the nest site he has to offer. This observation is compatible with the hypothesis that female house wrens choose mated males because they gain access to high-quality nest sites.