Polygyny in the yellow-headed blackbird: female choice versus male competition

Several assumptions and predictions of the polygyny threshold and sexy son hypotheses, which were proposed to explain the maintenance of polygyny on the basis of female choice, were examined. An alternative neutral mate choice hypothesis in which male competition is responsible for polygyny was also examined. For the yellow-headed blackbird, Xanthocephalus xanthocephalus, neither territory nor male features affected female choice of mate or female reproductive success. In the study population, polygyny occurred because males competed to hold territories in order to gain access to females. Since females settled apparently randomly, males that were more aggreessive and were therefore able to secure large territories had larger harems. Several criteria must be met in order for the neutral mate choice hypothesis to apply. Evidence from the literature suggests that for some species the criteria are not met and polygyny occurs due to female choice. However, several studies provide evidence that the neutral mate choice hypothesis may apply in some populations.