POLYGYNY IN THE RED-WINGED BLACKBIRD - DO FEMALES PREFER MONOGAMY OR POLYGAMY

Five hypotheses have been proposed to explain polygyny in the red-wing ed blackbird (Agelaius phoeniceus). We categorized the hypotheses into three groups based on female preference for unmated versus monogamous ly mated males: (1) the ''polygyny threshold'' model, ''sexy son'' hyp othesis and the ''asynchronous settlement'' model, which assume that f emales prefer unmated males to mated males on breeding situations of h omogeneous quality; (2) the ''neutral mate choice'' hypothesis, which assumes that females have no preference; and (3) the ''cooperative fem ale choice'' model, which assumes that females prefer monogamously mat ed males to unmated males. We tested the direction of female preferenc e in two field experiments. In both experiments, newly settling female s were given a choice of two adjacent territories, one defended by an unmated male and the other by a monogamously mated male. Male mating s tatus was randomized with respect to the variation in territory qualit y and male quality. Early in the breeding season, significantly more f emales settled with the unmated males than with the mated males. Altho ugh more females settled with the unmated males than with the mated ma les late in the breeding season, the difference was no longer signific ant. Female settlement late in the season appeared to be related to th e tenure of the resident females: the new females avoided territories where the resident females were in early stages of their nesting, but settled on territories where the resident females were in late stages. The pattern of female settlement shows that females prefer unmated ma les to mated males. The preference is consistent with the polygyny thr eshold model, sexy son hypothesis and the asynchronous settlement mode l, and inconsistent with the neutral mate choice hypothesis and the co operative female choice model. For this reason, the latter two hypothe ses are unlikely to explain the occurrence of polygyny in our populati on of red-winged blackbirds.