Dominance Relationships in Harems of Female Red-Winged Blackbirds

We investigated the factors determining dominance in aggressive encounters between female Red-winged Blackbirds (Agelaius phoeniceus) resident on territories of single males. Three male territories were observed, with harems of 5, 5, and 3 females. Feeding platforms were placed on the territories to increase the sample of observable encounters between residents. Order of settlement on the territory was strongly related to dominance; in 19 of 23 dyads the earlier settler won the majority of encounters. Proximity to the nest at the encounter site was also related to dominance; in 30 of 45 dyads the female closer to her nest won the majority of interactions. The effect of proximity on dominance also was shown experimentally by moving the platforms from near one nest to near another, which caused the dominance relationships between the pairs of females to reverse. In a partial correlation analysis, both order of settlement and proximity to nest correlated independently with the percentage of encounters won within dyads. Size, age, and nesting stage were not related to dominance.