POLYGYNY IN BIRDS - THE ROLE OF COMPETITION BETWEEN FEMALES FOR MALE PARENTAL CARE

In many polygynous birds the reproductive success of females is strongly dependent on male parental care, and females mated with the same male will compete for a limited amount of male assistance. Mated females may benefit from trying to prevent or delay the settlement of other females. Hence, female aggression may affect male mating success and thus play a role in the evolution of avian mating systems. We present a modified version of the polygyny threshold model that takes female aggression into account. A review on female aggression, male allocation of parental care, and delayed breeding of secondary females supports the model. An alternative model also predicts delayed breeding of secondary females when they benefit from reducing the breeding overlap with the respective primary females. However, recent studies suggest that secondary females may benefit from breeding as early as possible relative to the primary female. Our review also shows that secondary females generally have a reduced reproductive success compared with simultaneous, monogamous females. This difference may arise from a restricted mate search by females and does not necessarily contradict the polygyny threshold model.