Collaborative Research: Testing Alternative Hypotheses for the Maintenance of Behavioral Differences among Populations

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This project will be a continuation of combined field and laboratory studies designed to determine the factors responsible for the maintenance of vocal dialects in the brown-headed cowbird. The research will be carried out collaboratively by Dr. Stephen I. Rothstein of the University of California, Santa Barbara, and Dr. Robert C. Fleischer of the University of Hawaii. Their research will include (1) an intensive study of vocal variation within one large dialect, to determine if variation at different geographic scales is important to communication, (2) investigations of additional vocalizations besides the one emphasized so far, to determine if all vocalizations vary in the same manner, and (3) extensive banding, morphological, and biochemical studies, to determine if dialects are differentiated genetically and the degree to which birds disperse from one dialect to another. Such studies are important because dialects are prevalent among songbirds, yet are poorly understood. One hypothesis for the maintenance of dialects asserts that vocal differences facilitate reproductive isolation among populations. This hypothesis attributes major evolutionary significance to dialects and even suggests that they may influence rates of speciation. Because avian studies have played a major role in the formulation of modern theory about the origin of new species, dialect studies may contribute to our understanding of this critical aspect of evolutionary biology. Dialects are also important because the vocal differences that characterize them are learned and, therefore, represent cultural differences. These avian cultural differences may be the best analogs among animals of the cultural differences that characterize human populations. Information that Drs. Rothstein and Fleischer have gathered so far on the cowbird does not support the reproductive-isolation hypothesis. Instead, males seem to disperse and learn new dialects, but are at an initial disadvantage until they learn their new dialect. This process parallels human behavior in that people moving from one country or one profession to another are also at a disadvantage until they learn the language of their new country or the jargon and technical terms of their new profession. Lastly, this project is also important because the cowbird is a parasitic species that is a threat to several endangered bird species. Basic knowledge derived from the project may be used to increase the effectiveness of intensive cowbird-control programs currently being conducted by Federal and State governments in parts of Michigan and California.