Master of Science (MSc)
Faculty of Science
An integrative approach to biological research has facilitated the study not only of specific phenomena, but of the connections between these phenomena. A particularly striking example is that of the relationships between testosterone, social behavior, and social context. Increased levels of testosterone increase the frequency of aggressive behaviors and reduce the quality of parental care in many songbird species, and these changes in behavior can affect the surrounding social environment. Different social contexts, population density as a readily studied example, affect the cues that control the release of testosterone into the bloodstream. The distinct tan-stripe and white-stripe phenotypic morphs of white-throated sparrows (Zonotrichia albicollis) allowed these relationships to be closely examined in this species. Radioimmunoassay of blood samples obtained from tan-stripe and white-stripe males living in populations of high and low density did not reveal significant differences in testosterone levels across morphs or population densities. Population density and phenotype had an interaction effect on dawn chorus length, but no effect of testosterone on dawn chorus performance was found. White-stripe males sing more vigorously at dawn than tan-stripe males. Path analyses established that significant relationships existed between phenotype and dawn chorus performance, and that population density and testosterone levels did not have significant effects. In conclusion, the relationships between testosterone, social behaviour and social context could not be found in white-throated sparrows when dawn chorus and population density were taken as measures of social behavior and context, respectively. Evaluating non-androgen hormones, androgen sensitivity, daytime singing or different stages of the breeding season might reveal trends not detected in this study.
Hall, Simon Richard, "Population Density, Circulating Testosterone and Dawn Chorus Behaviour in White-Throated Sparrows (Zonotrichia albicollis)" (2009). Theses and Dissertations (Comprehensive). 935.