The moderately diverse group of birds in the family Corvidae includes crows, magpies, nutcrackers, and choughs. Their similarity to other large-brained, long-lived animals with complex social behavior suggested that it would be fruitful to explore the nature of their communication in light of their sociality. American Crows have an unusual breeding system among birds. They are cooperative breeders, which means that individuals other than parents assist in raising the young. In the case of American Crows, these helpers are the older siblings of the new offspring. By studying cooperative breeding in crows and the structure and function of their acoustic signals, we aimed to understand the evolution of complex communication more generally.
In Ann Arbor, Michigan, as in other populations, we found that the presence of helpers did not increase the reproductive success of parents (at least in the short term), but American Crows have an unusually fluid set of social options even among cooperative breeders. Some birds remain on and help defend their natal territories, year round, even while occasionally participating in smaller wandering flocks or large winter flocks. Other birds migrate as far south as Tennessee. Despite the graded and harsh nature of long-distance cawing, we were able to characterize stereotypy in rhythm and combinatorial complexity. Through seasonal field observations and controlled playback experimentation we determined that these song-like vocalizations are associated with territorial behavior. Thus the importance of fluid social situations appears to be reflected in the shaping of territorial vocalizations.
The dissertation can be obtained from UMI's Dissertation Express, publication number 9722061, or by interlibrary loan through your university.
Side projects on corvids include footedness, stone-carrying, neuroanatomy, and systematics in the genus Corvus.
My postdoctoral research with Jae Chun Choe and his students, Myung Bok Lee and Sang Im Lee and Youna Hwang, at Seoul National University extends this work on corvid behavioral ecology to address the molecular systematics of magpies in the genus Pica. Our results suggest that the two distinct magpie taxa in North America, both relatively social, are sister taxa most likely resulting from a single colonization from a more territorial Asian ancestor.