NEST-SITE QUALITY, FEMALE MATE CHOICE, AND POLYGYNY IN THE HOUSE WRENTROGLODYTES AEDON

Many models proposed to explain the occurrence of polygyny in birds im plicitly assume that females actively choose males offering the highes t quality breeding situations. However, strong evidence of active mate choice by females in polygynous bird species is scarce. This study as ked whether females in a polygynous population of house wrens Troglody tes aedon, a small, cavity-nesting songbird, base their choice of a ma te at least partly on characteristics of the nest site that he control s. Already-mated males were randomly assigned one of two types of nest boxes to which they could attempt to attract secondary mates. Some ma les were given standard-type boxes with small entrance holes in the fr ont sides of boxes, while other males were given boxes with larger ent rance holes located in tile boxes' roofs. A preliminary experiment rev ealed 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 m ated males with roof-entrance boxes significantly more often than expe cted by chance. This preference demonstrates that female house wrens d o discriminate among potential mates and base their choice of a mate a t least partly on characteristics of the nest site he has to offer. Th is observation is compatible with the hypothesis that fern ale house w rens choose mated males because they gain access to high-quality nest sites.