Vocalization behavior of captive loggerhead shrikes was studied at the Avian Science and Conservation Centre of McGill University. In the first stage, calls of two pairs kept in indoor cages were individually recorded not only to catalogue these calls spectrographically and quantitatively but also to use them in identifying the birds sexually. Males vocalized 21 call figures for 16.50% of the observation time and females, 8 call figures for 2.64% of the observation time. Males contiguously delivered 1 to 11 bouts with a mean of 7.25 min for a rate of 6.06 bouts/h; females delivered 1 to 9 bouts with a mean of 4.07 min for a rate of 1.27 bouts/h. Males not only vocalized at a higher rate and longer than females, but also demonstrated trill calls which the females did not do. In the second stage, five pairs were paired in large outdoor breeding pens. Their calls were recorded and current visual displays observed in an effort to understand calls related to breeding behaviors. Two new calls figures vocalized by males as well as 2 call figures by young shrikes were recorded. Each male demonstrated distinctive calls that differed from those of other males during nest-site selection, nest building and copulation, but similar calls during food offering, aggressive and alarm behavior. Despite the call differences, all males performed similar visual displays during the above activities. Conversely, breeding females gave no calls, other than harsh calls during food offering, food begging, aggressive and alarm behaviors.

Sexual differences are dramatic and widespread across taxa. However, a common genome between males and females should hinder phenotypic divergence. In this thesis I have used experimental, genomic, and theoretical approaches to study processes that can facilitate and maintain differences between males and females. I studied two mechanisms for the evolution of sexual dimorphism - condition-dependence and gene duplication. If sex-specific traits are costly, then individuals should only express such traits when they possess enough resources to do so. I experimentally manipulated adult condition and found that the sex-biased gene expression depends on condition. Second, duplication events can permit different gene copies to adopt sex-specific expression. I showed that half of all duplicate families have paralogs with different sex-biased expression patterns between members. I investigated how current sexual dimorphism may support novel dimorphism. With regards gene duplication, I found that related duplicates did not always have different expression patterns. However, duplicating a pre-existing sex-biased gene effectively increases organismal sexual dimorphism overall. From a theoretical perspective, I investigated how sexually dimorphic recombination rates allow novel sexually antagonistic variation to invade. Male and female recombination rates separately affect invasion probabilities of new alleles. Finally, I examined the assumption that a common genetic architecture impedes the evolution of sexual dimorphism. First, I conducted a literature review to test whether additive genetic variances in shared traits were different between the sexes. There were few significant statistical differences. However, extreme male-biased variances were more common than extreme female-biased variances. Sexual dimorphism is expected to evolve easily in such traits. Second, I compared these results to findings from the multivariate literature. In contrast to single trait studies, almost all multivariate studies of sexual dimorphism have found variance differences, both in magnitude and orientation, between males and females. Overall, this thesis concludes that sexual dimorphism can evolve by processes that generate novel sexual dimorphism or that take advantage of pre-existing dimorphism. Furthermore, a common genome is not necessarily a strong barrier if genetic variances differ between the sexes. It will be an exciting challenge to understand how mutation and selection work together to allow organisms differ in their ability evolve sexual dimorphism.

This thesis investigates the evolution of two secondary sexual characters in birds, large male body size and exaggerated male tail length. To determine whether the elaboration of these two characters is associated with two correlates of sexual selection intensity, mating system and parental care, I collected and examined morphological information for 1,990 species and natural history data for 745 species. Comparative studies should account for the problem of related species sharing similarities through common descent, so here I investigate associations with contrast scores that measure the variation radiating from unique ancestral nodes in a phylogeny. I show that greater polygyny correlates strongly with increasing male size but only slightly with longer male tail length, and that lesser paternal care correlates strongly with both traits. These results indicate that the evolution of increased male body size and exaggerated male tail length in birds is substantially influenced by the intensity of sexual selection.

Bibliography: leaves 274-289. / xiii, 289 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The mechanisms underlying the evolution of sexual size dimorphism in honeyeaters were investigated the Crescent Honeyeater, Phylidonyris pyrrhoptera. Ecological data was acquired at the Cromer Conservation Park, and Parndana, South Australia. / Thesis (Ph.D.)--Adelaide University, Dept. of Environmental Biology, 2001

Dissertation (Ph.D.)--Auburn University, / Abstract. Includes bibliographic references.

Thesis (Ph. D.)--Illinois State University, 1981. / Title from title page screen, viewed March 22, 2005. Dissertation Committee: Mathew J. Nadakavukaren (chair), John L. Frehn, Derek A. McCracken, Arlan R. Richardson, Fritz E. Schwalm. Includes bibliographical references (leaves 113-124) and abstract. Also available in print.

Thesis (Ph. D.)--Australian National University, 2003. / Title from PDF title page (viewed May 12, 2005). Includes bibliographical references.

Thesis (M.A.)--Texas State University--San Marcos, 2009. / Vita. Appendix: leaves 28-40. Includes bibliographical references (leaves 41-43). Also available on microfilm.

Thesis (M. S.)--Biomedical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Boyan, Barbara; Committee Member: Bonassar, Lawrence; Committee Member: Sambanis, Anthanassios; Committee Member: Schwartz, Zvi; Committee Member: Wick, Timothy.

Thesis (M.S.)--Georgia Southern University, 2006. / "A thesis submitted to the Graduate Faculty of Georgia Southern University in partial fulfillment of the requirements for the degree Master of Science" ETD. Includes bibliographical references (p. 89-95) and appendices.