Polygyny in marsh wrens: asynchronous settlement as an alternative to the polygyny-threshold model

Five predictions of the polygyny threshold model (PTM) were tested for a population of Cistothorus palustris. Contrary to the predictions of the PTM, male and territory quality were not correlated with male pairing success, male pairing success was not correlated with female settlement order, and the success of secondary females was not correlated with the order in which they settled. However, the order of settlement of 1st and 2nd females was correlated, and the reproductive success of monogamous females and that of secondary females settling at the same time were equivalent. These latter results are consistent with the PTM, but they are also consistent with an alternative model based on the asynchronous settlement of harem females. Settlement of female marsh wrens in the same territory is asynchronous. In addition, nestling weight at 8 days correlates positively with the number of days between females. Staggered settlement reduces the overlap in nestling stages and presumably reduces competition for male help and food in the territory. Females could, therefore, reduce the costs of polygyny by staggering their settlement. -Author