UC Davis

Animal courtship—a set of behaviors with critical fitness consequences—is, at its core, a dyadic interaction between two individuals. However, the environment in which courtship occurs can be complex. In addition to the physical structure of the environment, which can influence courtship signaling and signaling behaviors, there is often a complex social environment as well. Individuals may have to contend with multiple competitors and potential mating partners simultaneously. Additionally, this complexity is rarely static; the habitat or social structure may be spatially or temporally variable. The ability for animals to flexibility adjust their courtship behaviors in response to the surrounding context can help animals successfully find a mate; individual differences in behavioral plasticity have far-reaching fitness consequences.In this dissertation, we investigate how some of this natural complexity influences courtship behaviors. Using greater sage-grouse (Centrocercus urophasianus), a species of lekking bird, as a model species, we conducted a series of experiments in wild populations to better understand sage-grouse courtship behavior in response to changes in the social environment and to variable habitat structures. In Chapter 1, using robotic female stimuluses, we experimentally induced a courtship encounter and then introduced a potential second courtship partner to compare the relationship between male display effort and partner number. In Chapter 2, we investigated the role of social information in sage-grouse display behavior and tested whether the transmission pathways of this social information varied with environmental context. In Chapter 3, we tested whether the visibility of locations in sage-grouse courtship environments was predictive of male strutting behavior. Chapters are described in more detail below. Chapter 1 details the results of a field experiment conducted to investigate the relationship between male sage-grouse display effort and female number. Considering a lek as a mating marketplace has served as a useful framework to understand courtship dynamics. This chapter develops this framework by investigating the economic idea of outside options—the investment decisions made during an ongoing negotiation when a second potential partner approaches. To test the hypothesis that male sage-grouse will adjust their courtship display effort in response to outside options in ways that influence their mating success, we first introduced a single biomimetic robotic female onto our two study leks to allow males to initiate a courtship display. Then, we either maintained the same social context for the entire experimental trial or introduced a second robot and scored male display behavior. By simultaneously modeling display rate and display persistence, we were able to measure multiple aspects of sage-grouse’s bout-structured display behaviors. While our results supported findings found in prior work—that sage-grouse males adjust their display effort in response to female behavior—we found no evidence that sage-grouse males adjusted their display behavior when a second female is introduced, contrary to our prediction. Our results highlight the usefulness using the mating marketplace as a framework in which to investigate complex courtship dynamics. Chapter 2 highlights the role of social information use and transmission in male sage-grouse courtship displays. Female sage-grouse partake in mate-choice copying, a type of social learning, and it has long been theorized that males use social information to inform their display behavior. In this chapter, we experimentally introduced a cue of female presence (through either a robot or a playback) to a sage-grouse lek that was either visually open or experimentally manipulated (with a barrier) to be visually occluded. We then tracked the male behavioral response to our cue and used network-based analyses to quantify the use of social information about female presence on sage-grouse leks. We found evidence that, across all contexts and modalities, male sage-grouse use social information to inform their strutting behavior. Additionally, by comparing multiple potential transmission pathways, we demonstrate that sage-grouse flexibly use social information through different pathways depending on the treatment type. We also provide evidence that, in some transmission pathways, adding a visual obstruction changes the degree of social information use. Lastly, we found a bias in social information flow depending on male mating success in some networks. In addition to quantifying social information use in sage-grouse males, our work shows that animals may exhibit plasticity in gathering social information across complex natural habitats. Understanding the role of social information use and pathways of transmission, especially in fitness-critical behaviors such as courtship, can inform better conservation methods and habitat management strategies. Chapter 3 demonstrates how fine-scale mapping technologies can be used alongside behavioral experiments to test the influence of habitat structure on animal behavior. Sensory drive predicts that the characteristics of an animal’s environment will shape its signals and signaling behavior. The effects of habitat structure on signal structure are well demonstrated but the impacts on habitat choice at the individual scale is less understood. We experimentally induced courtship behavior in sage-grouse by presenting males in sage-dense, visually occluded areas with a female stimulus (either a robot or a playback) and recorded male display behavior. We combined this behavioral data with fine-scale habitat renderings of our study sites. In doing so, we were able to test the hypothesis that visibility (both horizontally and directly between the male and female) predicts locations where sage-grouse strutted (as opposed to random, nearby locations). We found that lower horizontal visibility indicated a higher chance that a location was a strut location and, counter to our prediction, that direct line-of-sight visibility did not predict strut location.