Abstract and Summary
Female red-winged blackbirds (Agelaius phoeniceus) often vocalize near their nests and so risk divulging nest locations. In a field study conducted during the 1983 breeding season in south-central Washington, USA, females vocalized upon departing and arriving at their nests during their pre-incubation, incubation and nestling-feeding phases. Females tended to utter Type 1 songs in these situations, a type thought to be used for pair-bond maintenance. One hypothesis to explain these vocalizations, that they are directed at mates to signal them of female movements, was rejected because the vocalizations were given regardless of male presence on territory. Another hypothesis, that the vocalizations are directed at other females to coordinate group departures, was rejected because most females departed singly and females did not leave their nests in response to playback of Type 1 song. We present an alternative hypothesis, that Type 1 song given in nest-associated contexts functions in intra-pair communication and particularly in individual and reproductivestatus identification of females. Males would benefit from such a system by being able to differentiate polygynous mates from each other and from other females, while females would benefit by constantly reinforcing pair-bonds and obtaining sexual non-interference during incubation and nestling phases.