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.

In this dissertation, I investigate the roles that aquatically derived resources play in the community structure and foraging behavior of wild birds in high-elevation regions of the Sierra Nevada mountains of California. Wilderness designations protect ecologically important areas from intense human development, which is critical to conserving them but also poses a challenge in accessibility to studying them. To address the need for data-rich methodology in wilderness, I piloted the use of passive acoustic monitoring (PAM) to collect data on the community composition and activity of birds breeding in alpine areas in 6 headwater basins throughout Sequoia and Kings Canyon National Parks (SEKI). In my first chapter, I investigated the potential for acoustic indices—mathematical measurements of variation in acoustic activity—to be used as proxies for avian diversity within three large acoustic datasets from U.S. National Parks that differ in spatial breadth and gamma diversity. Using a Random Forest with several widely used acoustic indices to predict observed species richness in 5,670 minutes of audio recording, I found that acoustic indices predict coarse but not fine differences in species richness. I discuss opportunities and limits in the application of acoustic indices as reliable measures of avian diversity in research and management contexts. Trout introductions to historically fishless high-elevation lakes cause trophic cascades within the aquatic system, resulting in simplified, species-poor food webs and major reductions in aquatic insect emergences. In the Sierra Nevada, over half of all historically fishless lakes now contain self-sustaining populations of trout, but the effects of this landscape-level disturbance on the surrounding terrestrial food web are largely unknown. In my second chapter, I investigated whether introduced trout impact the adjacent avian community via a reduction in aquatic insect emergences, a potentially valuable food source for birds. While avian alpha diversity (species richness) did not differ between lake types, I documented significant turnover in community composition, with fish-containing and fishless lakes diverging in the relative abundances of several alpine bird species common in the regional species pool. Differences in overall avian abundance between lake types approached statistical significance but were subtle: estimated avian abundance at fishless lakes was higher by roughly 1 individual per 300m sampling radius. Preliminary analysis of a Before-After, Control-Impact experiment involving fish removal at a study lake revealed a significant twofold increase in overall bird abundance following trout removal. The magnitude of this increase in bird abundance may be indicative of a response to a short-term increase in aquatic primary production but may also suggest that currently fish-containing lakes would be capable of hosting a greater abundance of birds in the absence of trout. The third chapter investigates how seasonality shapes the role of aquatic resources in the diets of breeding mountain white-crowned sparrows (MWCS). I used stable isotope analysis of carbon and nitrogen to quantify both trophic position and origin (aquatic or terrestrial) of the diets of nestling MWCS. Both trophic position and the proportion of food of aquatic origin of nestling diet changed directionally over the course of the season, with late-hatching nestlings being provisioned a diet both lower in trophic position and in aquatically derived prey than early-season nestlings. I discuss the nutritional benefits of aquatic prey items to consumers and how both seasonality and resource availability may impact both adult provisioning behavior and nestling quality. As global climate change accelerates warming and drying, especially in the alpine and at high latitudes, I argue that understanding the dynamic connections between the aquatic and terrestrial food webs is necessary to identifying, managing, and conserving climate refugia in these areas. Through observational and experimental field study at both the landscape and individual scales, I elucidate previously undocumented links between aquatic and terrestrial systems, demonstrate how the introduction of fishes to high-elevation waterways disrupts those linkages, and provide information about methodologies that can aid in efficient, data-rich, and minimally invasive research in critically important and imperiled wilderness areas.

With increased development and expanding urbanization, there has been a rise in anthropogenic noise pollution. This alteration to the natural acoustic environment has significant impacts on a wide variety of species. However, not all species—nor individuals within a species—respond to noise pollution in the same way. Intrinsic factors such as sex, age, and behavioral tendency all contribute to intraspecific variation to responsiveness to environmental disturbances, including noise. Here, I explored how individual differences contribute to variation in response to noise during the breeding season. I did this by exposing nest boxes settled by established populations of tree swallows (Tachycineta bicolor) to experimental playbacks of traffic noise. First, I sought to determine whether relative differences in aggressive tendency of mated pairs explained differences in reproductive success under noise exposure. I found that in nest boxes exposed to low noise levels, pairs that were more similar in aggressiveness raised slightly larger nestlings than pairs that were more different in their aggressive tendencies, but under high noise, pairs that were more similar in aggressiveness exhibited a significant reduction in nestling size. I examined parental care to find a mechanism for this effect, but I found that noise exposure did not affect incubation, provisioning rate, nor vigilance behavior while at the nest box. However, I did find that aggressive tendency explained male provisioning rate, with a decrease in provisioning observed in highly aggressive males, but no effect in females. Upon observing an effect of mate pair similarity on reproductive success in the context of noise, I examined whether individual aggressiveness, sex and quality played a role in settlement decisions, and could potentially impact mate assortment, and thus reproductive success. In a second experiment, I began noise exposure at the breeding grounds prior to territory establishment. I found that for both males and females, aggressiveness significantly explained nest box choice in regard to noise exposure. Highly aggressive individuals avoided settling in boxes exposed to high noise levels. This resulted in positive assortative mating by aggressive tendency, with pairs in lower amplitude boxes exhibiting higher average aggressiveness than pairs in higher amplitude boxes. I found no relationship between noise and measures of adult quality (body condition, breast feather brightness, mantle feather saturation), and no measures of quality were correlated within mate pairs. Lastly, during the height of breeding of the settlement study, the tree swallow populations were exposed to an unprecedented spring cold snap, with temperatures dipping to approximately 15°C (59°F) during the day and 6.67°C (44°F) at night, resulting in high nestling mortality and nest failure. Therefore, my last chapter explored the effects this severe weather event on reproductive success in the context of noise. I evaluated what factors influenced nest failure, how mates rebounded after the storm, and whether noise exposure potentially exacerbated consequences to breeding. I found that nestling age played a large role in nest success, with most mortality observed in the mid-age nestlings, rather than the recently hatched nestlings, or nestlings close to fledging. We also saw impacts to time to fledging and growth from the cold snap, though we did not find evidence that exposure to noise exacerbated the effects from the cold snap. Nestlings that lived through the storm, exhibited a similar response to noise as found in prior studies, with nestling mass decreasing with exposure to noise. However, for nestlings that hatched later in the season, after the cold snap, we see no such effect of noise. Additionally, adults varied in their response to the cold snap. Second year females were the most likely adults to cease breeding after the cold snap, and females with brighter breast feathers renested after the cold snap the soonest. Overall, intrinsic differences between nestlings as well as adults explained variation in how our population of tree swallows coped with a sudden extreme weather event.

Chemical communication has been understudied in vertebrates, but no group has been more overlooked than birds, where scent guided behaviors are cryptic, and until recently, olfaction was considered unimportant. It is now well established that birds have a functional sense of smell, yet due to the relative infancy of this field, there is still little known about how chemicals inform the social lives of birds. The overarching objectives of this dissertation were two-fold. First, to increase our understanding of how chemical information aids avian breeding behavior; and second, to develop improved analytical methods for identifying and measuring bird-produced odors, with a focus on the volatile chemicals that may function in communication.With these two objectives in mind, I completed three projects to investigate how chemicals facilitate the reproductive lives of the Leach’s storm-petrel (Oceanodroma leucorhoa). This long-lived, monogamous seabird species is an ideal system for studying avian chemical communication. Leach’s storm-petrels perform their reproductive behaviors under the cover of darkness, but lack good vision in low light conditions, indicating a reliance on non-visual communication. Moreover, they have a large olfactory anatomy, an excellent sense of smell, and a pungent plumage odor. In the first chapter of this dissertation, I used gas-chromatography mass spectrometry to examine the social information present in the strong odor of Leach’s storm-petrels. I discovered that despite interannual variation, the feather chemicals reflected individual identity, which may help storm-petrels maintain their long-term mate bonds. In vertebrates, the immune genes of the Major Histocompatibility Complex (MHC) influence mate choice decisions and enable individual recognition. Moreover, MHC shapes body odor and organisms may use olfaction to evaluate the MHC genotype of conspecifics. In the second chapter of this dissertation, I tested the hypothesis that the plumage chemicals of Leach’s storm-petrels contain information about MHC. This study was motivated by a recent finding that male Leach’s storm-petrels make MHC-based mate choice decisions to select high quality females. I found that feather odors reflected two aspects of MHC genotype: similarity and diversity. These findings were particularly strong for females, which implicates olfaction as a likely mechanism enabling MHC-informed mate choice by males. Making trips to and from their nest is an important behavior that all birds must accomplish to ensure reproductive success. In the final chapter of this dissertation, I investigated how chemicals inform olfactory homing in Leach’s storm-petrels. I analyzed the odors associated with the colony floor, storm-petrel nests, and their avian occupants. I identified gradients of environmental chemicals across the colony, which may aid homing in storm-petrels. Furthermore, I discovered that storm-petrel chemicals are deposited inside the nest, creating unique nest odors that reflect the specific storm-petrel occupants. This is the first evidence of bird nests being scented by the owner’s body odor, which likely facilitates olfactory nest recognition in this species. In summary, the integrative research presented in this dissertation connects the fields of animal behavior, analytical chemistry, and molecular biology to highlight chemicals as an important source of information for breeding birds.