Date of Award
Doctor of Philosophy
Avian vocal communication and its role in agonistic encounters is well-studied, but many of its roles remain unclear. Studies suggest that exposure to conspecific calls activate the hypothalamo-pituitary-gonadal (HPG) and/or hypothalamo-pituitary-adrenal (HPA) axes in some species. Additionally, while vocal communication research has been dominated by research on male song, recent research has increasingly examined the role of females. I conducted a series of experiments in Florida scrub-jays (Aphelocoma coerulescens), a year-round territorial and highly vocal corvid that uses both intersex and female-specific calls, to investigate the role of vocal territory defense as an ecologically-relevant stressor in nestlings and adults, as well as the role of female vocalizations and aggression. I investigated the effect of vocal territory defense on nestlings by exposing broods to conspecific call playback. Nestlings exposed to call playback showed no difference in their levels of circulating corticosterone or testosterone over controls. However, nestlings exposed to conspecific playback exhibited a marginally higher corticosterone response to handling than control nestlings. To assess the role of female-specific calls in territory defense, I conducted call playback of male 'weep' and female 'rattle' calls throughout the breeding and nonbreeding season. Additionally, I captured males to test their corticosterone and testosterone responses following playback. In another experiment, I tested teh response of breeders to simulated 'pairs' using a dual-speaker playback design. Males and females each exhibited high intra- and inter-sexual aggression during both single- and dual-speaker playback, while females were more vocal and males approached playback sources more closesly. Males did not elevate testosterone or corticosterone in response to either call. Finally, I conducted playback of rattle calls at two sites with distinct dialects to explore the role of female vocalizations in sexual selection. Males and females at each site exhibited elevated aggression toward their local call dialect. Together, these results suggest that vocal communication does not stimulate HPG or HPA resposnes in this species; however, female vocalizations play a significant role in territory defense and sexual selection. This has implications both for future conservation of the declining Florida scrub-jay and the study of other species in which female aggression is prominent.
Dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.
Ferguson, Stephen Michael, "Vocal Aggression in the Florida Scrub-Jay (Aphelocoma coerulescens): Behavior, Hormones, and the Role of Females" (2017). Electronic Theses and Dissertations. 1682.