Song Sharing in a Group-Living Songbird, the Australian Magpie. Part Ii. Vocal Sharing Between Territorial Neighbors, Within and Between Geographic Regions, and Between Sexes

Abstract

In this study we investigate the role of song in the social behavior of a cooperatively living songbird, the Australian magpie, Gymnorhina ticbicen (Cracticidae). In this species, kin and nonkin cooperative territorial groups exist in the same population. We sampled the vocal repertoire of 23 magpies in six territorial groups and the nonterritorial flock. Groups were located on two farms 2-3 km apart. This paper is the second of a two part paper. In Part I, we described song, and song and syllable repertoires; and we compared song sharing within and among kin and nonkin groups. Our results in Part II include: 1. Local geographic patterns in repertoire sharing. We found the average percentage of the repertoire shared between all pairwise combinations of birds to be lowest for birds in different localities, intermediate for birds in the same locality who are not neighbors, and highest for birds who are group mates or neighbors (p 0.79, Mann-Whitney rank sum test) than by birds of the opposite sex, when all birds of known sex were considered. However, when we considered sharing by group mates or neighbors only, birds did share a significantly (p<0.008) larger percentage of their repertoire with birds of the same sex than with birds of the opposite sex. 3. Sources of vocal imitation. To determine the sources of imitation, we calculated the proportion of a focal bird's repertoire that is shared with different social classes of birds. Birds share more syllables exclusively with group mates than with neighbors, and they share more complex syllables with group mates than with other birds (p<0.001, G test of association). From these data, we discuss the role of vocal imitation in song learning, the timing and social setting of vocal learning, and the territorial functions of song. We conclude that vocal sharing through imitation may function in social affiliation within the group and in territorial defense between groups.