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The study of animal movement has remained of central importance to the study of animal behaviour, as a critical component of how animals survive and reproduce. Through an ever-increasing wealth of telemetry studies, the role of individual decision-making, in response to internal and external cues, has been recognised as important in shaping movement patterns. However, further work is required to better understand the mechanistic drivers and demographic consequences of these decisions, which underpin the long-term stability of populations. As the influence of anthropogenic stressors rapidly increases it becomes critically important to understand the capacity of different species to respond to possible threats. Here, I study a widespread and generalist seabird, the northern fulmar (Fulmarus glacialis), which has undergone a large population expansion in recent centuries but is currently in decline. Focussing on adult birds breeding at the colony of Eynhallow (Orkney Islands, UK) I build on recent tracking studies and past observational studies of this species, to better understand their individual movement patterns, possible drivers of these and links with breeding success. Fulmars from this colony use a range of movement strategies throughout the annual cycle, visiting the North Sea, the Norwegian Sea, the Mid-Atlantic Ocean and the Barents Sea, resulting in large variation in how far they travel from the colony (< 500 km to > 2000 km). In Chapter 3, I quantify individual consistency of movement patterns throughout their annual cycle. To separate behaviourally discrete periods throughout the year, I used a combination of daily summaries of location, light level and salt-water immersion, enabling me to quantify inter-annual variation in spatial distributions at individually relevant timescales. I find individual consistency throughout the non-breeding period, including in late winter, despite high levels of population-level consistency at this time and some instances of individual flexibility. In Chapter 4, I focus in more detail on late winter and pre-breeding, which in fulmars represent an extended period of central place foraging, where they associate with the breeding colony but still spend significant time at sea. There was large variation in trip-taking behaviour in both sexes. Males were more likely to remain resident, but large numbers of both sexes took multiple long foraging trips away from the colony, likely travelling thousands of kilometres more each year than their resident counterparts. I also find that females take longer trips than males and are more likely to revisit familiar areas on pre-laying exodus than males, suggesting biological differences in how fulmars trade off time spent foraging against time at the breeding colony. However, I find no evidence of variation between years, or of carry-over effects linking these behaviours with breeding success. In Chapter 5, I use high-resolution accelerometry data to describe almost instantaneous flight mechanics and provide insight into how fulmars achieve these highly transitory movements. I find surprising reliance on predominantly flapping flight for a Procellariiform seabird, and evidence that like other seabird species, fulmars moderate their energetic expenditure at different wind speeds, but no clear mechanistic link. Together, these findings suggest that in fulmars the importance of energy gain from dynamic wind features has possibly been over-estimated. This thesis expands our understanding of the movements of fulmars throughout their annual cycle, at broad and fine spatial and temporal scales. Making use of long-term data, I demonstrate how additional insight can be gained by using individually specific pattern recognition techniques, to augment the interpretation of low-resolution data. Additionally, I demonstrate the value of state-of-the-art high resolution data loggers, to mechanistically understand how broad-scale movements are achieved.

Recording animal movements is essential for understanding the distribution of species over time, with far-reaching consequences for fitness, population dynamics and conservation. Oceanic seabirds are some of the most mobile and threatened species on Earth, mainly because of incidental mortality (bycatch) in fisheries. Tracking these birds has improved our knowledge of how the environment and individual traits shape specific foraging and migratory strategies; however, this research is biased towards adult life-stages, which are easier to track. In particular, juveniles remain understudied, even though they are likely to differ in their critical habitats and overlap with fisheries, and hence bycatch risk, with implications for population trajectories. In this thesis, I capitalize on recent advances in tracking technology and the wealth of data collected on threatened albatross and large petrel species breeding at Bird Island, South Georgia, to investigate variation in spatial ecology and fisheries bycatch risk across multiple life-stages and species. In Chapter 1, I introduce the main topics of this thesis. In Chapters 2-4, I investigate how wind and resource availability shape divergent movement patterns between juveniles and adult life-stages, and identify age-specific bycatch risk. As high juvenile mortality is likely to result in an ageing population, in Chapter 5 I examine senescence in foraging behaviour, and consider the ramifications for population recovery. In Chapter 6, I then assess the effectiveness of existing fisheries bycatch mitigation measures by investigating the diving capabilities of the most bycaught species in the Southern Ocean. Finally, I conclude with a general discussion summarizing my main findings and suggesting future work. Overall, my results provide new insight into the capacity and motivation for movement in wide-ranging animals; highlighting the diversity of extrinsic and intrinsic processes shaping movements over the lifespans of individuals, and with implications for focusing conservation efforts in time and space.

Recent improvements in biotelemetry and analytical methods have increased our understanding of the at-sea movements and behaviour of elusive pelagic seabirds, many of which are becoming the focus of conservation efforts. In this thesis, I consider several issues related to the environmental correlates of the foraging movements and at-sea distributions of a critically endangered shearwater in UK waters and of two penguin species in Antarctic and sub-Antarctic waters; I also consider the use of the 'dual foraging strategy' (i.e., both short- and long-distance foraging) during chick-rearing of different seabird taxa. This thesis explores the associations of oceanographic variables and prey abundance with the at-sea distribution of both non-breeding seabirds (Balearic shearwater Puffinus mauretanicus, Chapter 2) and of breeding seabirds (macaroni penguins Eudyptes chrysolophus, Chapter 4). Chapter 2 combines 5 years of vessel-based surveys of post-breeding Balearic Shearwaters in the western English Channel and southern Celtic Sea with simultaneously collected bio-acoustics data of fish abundances and remote-sensed environmental data. I map Balearic shearwater presence across the area using both Generalized Additive Models (GAMs) and Random Forest (RF) models, providing the first estimate of the distribution of this critically endangered seabird in UK waters, information that is essential for the designation of a Special Protection Area (SPA). Oceanic variables associated with prey distributions were better predictors of seabird movements than direct measures of prey distribution, possibly because snapshots of prey availability cannot capture the dynamic nature of prey distributions. Using data from GPS and time-depth recorders, this thesis also investigates the presence and dynamic nature of prey depletion around breeding colonies in two penguin species (chinstrap penguins Pygoscelis antarcticus in Chapter 3, and macaroni penguins in Chapter 4) and estimates foraging patch quality based on time allocation during foraging dives. Foraging patch quality increased with increasing distance from the colony for both species, suggesting that birds depleted prey near their colony, providing evidence for "Ashmole's halo". However, neither species utilized the dual foraging strategy. Interestingly, habitat quality near the chinstrap penguin colonies improved over the breeding season, suggesting that chinstrap penguins, like some other seabirds, time their reproduction so that the period of maximum resource availability in the environment aligns with their period of maximum demand for resources. Finally, the drivers of dual foraging in different seabird families are identified in a systematic review (Chapter 5) that compiles published literature on the use of dual foraging by seabirds during chick-rearing with concurrent estimates of habitat quality around the colonies. We found the likelihood that seabirds use the dual foraging strategy increases with increasing magnitude of the difference in the quality of the habitat accessible during short- versus long-distance foraging trips. However, there were significant differences in the use of dual foraging across taxa: Albatrosses and Penguins were significantly less likely to dual forage than Procellariidae, while Sulids were significantly more likely to dual forage than Procellariidae. This suggests that other, taxon-specific factors - such as travel costs and the resilience of chicks against starvation - also play a role in determining the use of the dual foraging strategy by different seabird taxa. Overall, these findings advance our understanding of the environmental drivers of seabirds' foraging distributions and provide valuable information for their conservation.

This thesis brings together multiple strands of information at different temporal and spatial scales to shed new light on foraging behaviour. Foraging accounts for much of the time and energy budgets of wild animals and underpins many ecological and evolutionary processes. I used the central place foraging trips of a wide-ranging marine predator, the northern gannet Morus bassanus, as a model to study foraging ecology and the influences of fisheries and climate change. My five data chapters span a range of temporal scales, from two-second behavioural classification to interannual variation across 11 years, as well as a range of spatial scales from individual bird-boat interactions to a multi-colony comparison spanning 83% of the latitudinal range of breeding colonies. First, I found sex-specific foraging behaviour across a range of spatial, temporal and isotopic axes and that the extent of segregation varied inter-annually. Second, I examined the energetics of foraging behaviour, revealing the relative costs of different behaviours and how they relate to three-dimensional flight patterns. I found that effort was driven by the time spent performing behaviours rather than differences in the costs of behaviours per unit time. Furthermore, the proportions of each trip spent performing each behaviour were independent of trip length, meaning that foraging trip duration was a good metric of overall effort. Third, I used bird-borne videos cameras to reveal a high incidence of gannets scavenging from fisheries discards and trawl nets in the Celtic Sea. Scavenging is often thought to be an energy-saving strategy, but the energetic cost of scavenging was no different from that of natural foraging. Fourth, I found that gannets did not respond to nearby fishing vessels in Iceland, where discarding is banned and foraging effort suggested plentiful natural prey. Finally, I collated a large multi-colony dataset, which showed that foraging range and trip durations decreased with latitude when controlling for colony size. I related this pattern to poleward range shifting in response to climate change. Overall, I found that foraging behaviour is highly variable in some respects and consistent in others. This is driven by stable factors such as sex and colony location and changing factors such as population size, climate and oceanography, and fisheries practice or policy. This thesis particularly highlights the benefits of combining data from multiple sources, time periods and regions in order to reveal new patterns.

Animal movement is a ubiquitous process and can have consequences ranging from an individual’s energy expenditure to ecosystem dynamics. This study uses biologgers, primarily accelerometers, to record and examine the at-sea behaviours of black-legged kittiwakes (Rissa tridactyla) during their breeding period. Accelerometers record the acceleration of an instrumented animal to give an indication of their behaviour and movements, yet their output can be particularly difficult to interpret. As such, this thesis begins with a method developed for the assignation of coarse-scale behaviours to accelerometry data. The method is a simple yet objective approach intended to be widely applicable. Using this method, we construct time-activity budgets for incubating and chick-rearing kittiwakes and apply activity-specific estimates of energy expenditure to these behaviours. We identify how kittiwakes allocate their time and what the energetic consequences of variation in time-allocation are. We present empirical evidence for chick-rearing kittiwakes expending more energy than incubating birds and identify that kittiwakes exhibit behavioural compensation whereby they limit energy expenditure across both foraging trips and days. We also examine the flight behaviour of kittiwakes in relation to extrinsic conditions. We find that wind conditions do not seem to influence broader scale patterns in movements during foraging trips, however kittiwakes do display behavioural plasticity in response to wind conditions by optimising their flight speeds towards maximum range speeds. We also identify that to optimise flight speeds, kittiwakes change the strength at which they flap their wings, rather than the frequency. Finally we present a serendipitous observation of predation of kittiwake chicks by a peregrine falcon. Although not directly related to movement ecology, this study documents novel predatory behaviour and highlights the importance of biological forces other than movement. Overall, the work presented in this thesis demonstrates that by examining the movement of individuals, it is possible to gain insights into various important aspects of their biology.

Many animals including marine mammals and several seabird species dive in large groups, but the impacts that social interactions can have on diving behaviour are poorly understood. There are several potential benefits to social diving, such as access to social information or reduced predation risk. In this body of research I explore the use of social information by groups of diving animals by studying the behaviour of European shags (Phalacrocorax aristotelis) diving in “foraging rafts” in the Isles of Scilly. Using GPS tracking I establish where shags regularly forage in relation to bathymetry and areas where foraging rafts frequently formed. Using these data I show that the foraging ranges of different colonies overlap and that foraging ranges of individual shags are often predictable. This suggests that social information will be of less value while searching for foraging patches. However, using observational studies to further explore the conditions and areas in which foraging rafts formed, I show that advantages such as anti-predation or hydrodynamic benefits are unlikely to be the main drivers of rafting behaviour in the Scillies. I therefore suggest that access to social information from conspecifics at a foraging patch may be one of the main benefits diving in groups. Using a dynamic programming model I show that individuals diving in a group benefit from using social information, even when unable to assess conspecific foraging success. Finally I use video analysis to extract the positions and diving behaviour of individuals within a foraging raft and compare this to simulated data of collective motion and diving behaviour. The results of these studies indicate that an individual being able to utilise dives of conspecifics to inform their own diving decisions may be one of the main advantages of social diving.

All wildlife populations harbour parasites. However, seabirds are likely to play a particularly important role in the maintenance and dispersal of infectious agents as a result of their colonial breeding habits. Seabird colonies are also known to be highly spatially structured, but little is known about the effects of this spatial structuring on seabird parasite dynamics. In this thesis, I use a tick-borne virus, Great Island virus (GIV), found in a large common guillemot (Uria aalge) colony bordering the North Sea as a model system to explore this relationship. I use a multidisciplinary approach, framed by a simple epidemiological model of the guillemot-tick-virus system. In Chapter 2, I describe a novel epidemiological model and parameterise it using the existing literature. The model suggests the importance of spatial structure within the guillemot colony, but also identifies a key missing parameter, the rate of virus transmission between pre-breeding and breeding areas. In Chapter 3, I go on to test the potential role of independent tick movement in driving transmission between these two areas, by quantifying the mobility of host-seeking seabird ticks, Ixodes uriae. I show the potential for ticks to walk ranges described anecdotally in the literature, in just a few minutes, but stress the importance of further experiments in the field. Chapter 4, I test the potential role of guillemot-mediated tick movement between pre-breeding and breeding areas. I show that pre-breeding guillemots spend a limited proportion of time ashore during daylight hours, which increases significantly as the season progresses and varies between individuals. A similar pattern is observed when considering how often they enter breeding areas when ashore; generally infrequently but varying spatiotemporally and between individuals. In Chapter 5, I apply finite mixture modelling techniques to improve existing estimates of age- and strain-specific GIV seroprevalence and force of infection in the guillemot colony. I also provide the first estimates of these parameters for eight strains, and highlight the importance of understanding strain-specific differences in GIV dynamics in future studies. Finally, I bring all four data chapters together in Chapter 6, by inputting my new parameter estimates (Chapters 3-5) into my existing model (Chapter 2). Taken together, my results suggest that GIV transmission within the guillemot colony may increase in the future as a result of declining breeding abundance and success, with more frequent or extreme disruption leading to a higher risk of infection within the colony. More generally, my results suggest that seabird colonies can be highly sensitive to changes in their spatial structure, and that endemic parasites have the potential to substantially impact, and hence to be an added threat to, their seabird hosts.

Age-related variation in demographic rates has significant consequences for population and evolutionary dynamics, and understanding the processes driving such variation is therefore an important aspect of evolutionary ecology. Reproductive performance may vary over the lifetime of an individual, and this may be the result of both variations in reproductive effort and changes in individual competency. For example, increasing experience is likely to have beneficial effects on reproduction during early life, and senescence, or declines in physiological function, may have negative impacts on the performance of older individuals. The rate at which these changes occur can vary dramatically between species, and even between individuals of the same species. However, understanding the causes and consequences of this variation in the rate of ageing is not always straightforward. As well as the individual-level processes described, the phenotypic composition of successive age classes will contribute to age-related variation observed at the population level. Abrupt changes in performance, such as the poor performance of first time breeders, may be obscured if individuals vary in their age at first reproduction. Population-level patterns may also be influenced by selection; for example, the selective disappearance of low quality individuals from older age classes may mask senescent declines in the performance of longer-lived individuals. Moreover, the physiological mechanisms that underpin within-individual changes in performance are not well understood. Unravelling the drivers of such age-related variation requires longitudinal data, following individuals throughout their lives, which presents challenges for the study of natural populations. Albatrosses are among the longest lived vertebrates. In this thesis, I use data from three species of albatross breeding at Bird Island, South Georgia (54°00’S, 38°03’W) to explore age-related variation. Focusing primarily on the wandering albatross, Diomedea exulans, I characterise the relationship between age and various reproductive traits, and decompose the population-level patterns to reveal effects of experience, senescence and terminal effects across the reproductive lifespan of individuals. I then consider foraging behaviour as a proximate driver of changes in reproductive performance in this species. Using tracking data collected over a 20 year period, I find limited evidence for age-related variation in foraging trips taken throughout the breeding cycle. Going one step further, I explore telomere dynamics in the wandering albatross, examining the potential for telomere length to act as a physiological marker of individual state. Finally, I move on to a species comparison, incorporating data from the black-browed (Thalassarche melanophris) and grey-headed albatross (Thalassarche chrysostoma). I compare the population- and individual-level ageing patterns of these three closely related species, and consider these in light of their differing life history strategies.

Parasites are important drivers of ecological and evolutionary processes in their hosts. However, hosts often differ in how they are affected by parasitism, which can be important in how parasite effects on individuals scale up to the population level. Hosts may differ intrinsically in their susceptibility to parasitism, and extrinsic factors may impose constraints on how hosts allocate resources between immunity, maintenance and reproduction, thereby further affecting their ability to cope with infection. These extrinsic factors include the host’s ecological environment, for example food availability or weather, and its social environment, that is its interactions with conspecifics. This is particularly true during a reproductive attempt when individuals interact closely with other family members. Not only might immediate impacts of parasitism differ between and within parents and offspring, but the direct effects of parasitism on a host could have further indirect consequences for other family members through their behavioural interactions with parasitised individuals. The distribution of direct and indirect effects among all family members could affect the outcome of the breeding event and individuals’ future performance. However, teasing apart these various avenues of parasite impacts on families may be difficult if parasite burden or susceptibility is correlated between family members. In this thesis, I explore the consequences of parasitism for different family members of the European shag Phalacrocorax aristotelis infected with gastrointestinal nematodes, over a range of ecological conditions. In chapter 2, I demonstrate that chicks’ responses to anti-parasite treatment across four years vary between siblings and with environmental conditions, which may be mediated by resource allocation among siblings. In chapter 3, I explore how costs of parasitism are distributed among the whole family by simultaneously treating chicks and/or parents with an anti-parasite drug and measuring the outcomes for all family members. Treatment has a more marked effect for the non-treated generation than for the treated individuals, suggesting that parasitism may have important indirect costs. In chapter 4, I investigate whether within-brood variability in the effects of anti-parasite treatment and its cross-generational impacts are mediated by behavioural change, and show that chick treatment but not parent treatment influences several aspects of behaviour in the nest. In chapter 5, I demonstrate that the impact of chick anti-parasite treatment on parents persists beyond the breeding attempt, with parents of treated chicks foraging less overwinter and breeding earlier the following year, whereas there is no persistent effect of parents’ own anti-parasite treatment. Lastly, I provide an appendix examining the parasitology of the system in detail, including an assessment of in situ and proxy measures of worm burdens of chicks. This thesis demonstrates that parasitism can be a key component, previously overlooked, of reproductive performance in seabirds, a group that plays an important ecological role as apex predators and thus indicator species of the marine environment.

Marine vertebrate species face unprecedented and ever increasing pressures as a result of human activity, primarily fishing, in the global oceans. One area of growing concern has been for the impacts of small-scale fisheries on these species. Over the past decade it has become increasingly clear that these under-studied fisheries have sizeable levels of catch and bycatch of many threatened and endangered species of sea turtles, seabirds and small cetaceans. This thesis presents a collection of chapters that investigate aspects related to the interactions of small-scale fisheries with threatened marine vertebrates. We identify sizeable rates of bycatch of small cetaceans and seabirds for multiple small-scale longline and gillnet fisheries in both Peru and Ecuador. Catch rates of small cetaceans by the Peruvian small-scale driftnet fleet are estimated to exceed 10,000 dolphins and porpoises annually. A trial of acoustic alarms (pingers) in this same fishery showed a 37% reduction in small cetacean bycatch while not reducing target catch and represents a promising bycatch mitigation measure. Seabird bycatch was also found to be high in both longline and gillnet fisheries and included a wide range of seabird species including the critically endangered waved albatross (Phoebastria irrorata). Through post-capture satellite tracking of loggerhead turtles (Caretta caretta) we show that these turtles are present in pelagic waters off the coasts of Peru and Chile for extended periods during which they are at risk of repeat interactions with small-scale longline fisheries operating throughout their foraging habitat. Through scan and focal sampling of the endangered marine otter (Lontra felina) we also show that otters making den sites in human fishing communities face additional risks due to entanglement in fishing gear or interactions with feral animals but, if properly managed, these sites could serve as stepping stones for marine otters along the coast. The results presented here, gathered using a wide range of techniques, including onboard observer and shore-based monitoring, satellite tracking, bycatch quantification, and bycatch mitigation experiments, represent an attempt to better characterize and quantify the interactions of small-scale fisheries with threatened marine vertebrates toward identifying solutions that can lead to sustainable fisheries and populations of these protected marine species.

Seabirds are vulnerable to a wide range of impacts at sea and function as important indicators of ocean health. A detailed understanding of their movements and distributions at sea, as well as the types of behaviour in which they engage and the extent to which those activities make them vulnerable to different impacts is critical in effective conservation planning. But their elusive lifestyles and mobility have hampered studies of their at-sea behaviour. Using miniature data loggers deployed on Manx shearwaters Puffinus puffinus this thesis explores the movements, distribution and behaviour of a small-medium pelagic, procellariiform seabird during foraging trips at sea. Foraging distributions were most variable during the pre-laying period when females departed the colony to build their egg. Females foraged close to the colony when local resources were adequate, but more typically foraged in distant shelf edge waters. Males returned frequently to the colony during this period and typically foraged close by, but also in shelf edge waters when local resources were poor. During incubation and chick-rearing the foraging movements of birds tracked from up to four colonies showed considerable inter-annual variability, but were largely constrained to the Irish and Celtic Seas and the inshore waters of west Scotland. Birds from each of the colonies foraged in waters local to their own colony, but also in more distant locations, including the productive Western Irish Sea and Western Irish Sea Front where birds from multiple colonies co-foraged, presumably at high densities. At-sea behaviour was organized into three principal activities representing: (1) sustained direct flight, (2) sitting on the sea surface, and (3) foraging, comprising tortuous flight interspersed with periods of immersion and diving in pursuit of prey. Foraging was highly constrained to daylight hours during which birds engaged in bouts of diving separated by periods of flight or rest on the surface. Most dives were up to 6 m deep, lasting up to 13 s, but some much deeper dives (maximum 55.5 m) were also made. During chick-rearing the use of short and long duration trips may allow parents to control provisioning effort and their own body condition. However, reducing parents’ requirement to provision their chick (by supplemental chick feeding) did not appear to alter the at-sea movements and behaviour of parents, suggesting that at-sea behaviour probably is controlled more by foraging conditions and prey distributions than by the nutritional demands of the chick.

Microplastic presence and its potential adverse impacts on wildlife are not yet well understood in coastal ecosystems. Using standardized methods such as an alkaline tissue digestion and Raman spectroscopy, we quantified the presence, category (e.g. fiber or fragment), and polymer identification of microplastics (particle size < 5 mm) in three representative sample types of the coastal system: seawater (n=12 17 h trials), northern anchovies (Engraulis mordax, n=24), and common murres (Uria aalge, COMU, n=19). We assessed the recovered microplastics from COMU for xenoestrogenic activity using an in-vitro estrogen receptor activation assay. Particles were recovered from all sample types: 100% prevalence in the 17 h seawater trials, 58% prevalence in anchovies, and 100% prevalence in COMU. Fibers were the most abundant particle (77%), followed by fragments (13%), foam (5.8%), film (2.0%), and bead (0.78%). Raman spectroscopy identified 11 out of 20 particles that were microplastic (synthetic, semi-synthetic, or blends) as polyester. In addition, particles recovered from digestive tracts of three common murres had potential xenoestrogenic activity. To our knowledge, this study is the first to analyze and provide baseline information on the presence and potential hormone-disrupting activity of microplastic in the Monterey Bay (California) coastal system.

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.

The modulation of energy balance through physiological or behavioral adjustments (i.e., allostasis) allows organisms to cope with unexpected challenges, ensuring reproductive success and survival. However, energetic challenges can be exacerbated during critical life stages such as breeding, when more resources are needed to feed offspring. Amphibious marine organisms like seabirds already face a unique challenge of finding patchily distributed ephemeral prey within a vast, dynamic ocean and delivering prey to hungry chicks at land-based nests. With the depletion of ozone and rising sea temperatures, atmospheric and oceanographic disruptions are escalating, affecting the distribution of prey in addition to altering windscapes that seabirds, like the glider-shaped albatrosses, rely on for traveling. Metabolic stress hormones in seabirds can be used to indicate adverse changes within the environment; however, the functional role of stress hormones is confounded by factors such as species, life history, or breeding stage. In chapter 2, I used structural equation models to improve our understanding of the role of corticosterone, a stress hormone, as a mediator of energy balance in two sympatric breeding albatrosses during incubation and early-chick-rearing stages. Campbell (Thalassarche impavida) and grey-headed albatrosses (T. chrysostoma) are annual and biennial breeders, respectively, that occupy differing prey niches. By measuring foraging behavior, mass change, and hormone levels, I found that corticosterone concentrations before and after foraging trips were similar between species and across stages, potentially because of behavioral flexibility or different corticosterone functional roles across stages. However, when parents were provisioning small chicks during the guard stage, the former were more sensitive to changes in energy balance, suggesting that hormone concentrations elicited during this stage are indicative of foraging conditions. Also, pre-trip corticosterone may determine foraging destination in incubation-stage Campbell albatrosses, but it remains unclear if this mediates foraging success. In chapter 3, I examined the role of environmental interactions, behavioral flexibility, and morphological constraints on energy balance during early chick-rearing using the doubly labelled water method to estimate the daily energy expenditure (DEE) of GPS tracked individuals. In both species, greater DEE was associated with greater foraging success, lower mean wind speeds during water take-offs, a greater proportion of strong tailwinds (> 12 ms-1), and younger chick age. Greater foraging success was marginally costlier in male albatrosses of both species and DEE was higher in grey-headed albatrosses when they experienced a greater proportion of strong headwinds. Climate models predict wind speeds will weaken in the foraging range of female Campbell albatrosses and intensify in the range of grey-headed and male Campbell albatrosses, thus breeding costs may increase for both species. In chapter 4, I used a flight cost function to show that mean flight costs were greater during the incubation stage for grey-headed albatrosses, which may interrupt breeding cycles. I then used reanalyzed wind data in combination with bird-borne GPS tracking data to score the cost of flight path trajectory choices and to calculate vector correlation coefficients to evaluate wind-use consistency. Greater wind-use consistency resulted in lower mean flight costs and greater foraging success for both species, but Campbell albatrosses that use low-wind regions had the greatest wind-use consistency. Males of both species gained less mass than females when making similar cost choices during incubation stage transit. Chick-rearing individuals of both species traded greater cost choices for greater foraging success during outbound transit. Overall, foraging strategy, mediated by hormones and morphology, revealed energetic vulnerabilities with respect to species, sex, and breeding stage.

This dissertation aims to contribute toward the understanding of water-entry and -exit behaviors in nature. Since water is nearly a thousand times denser than air, transitioning between the two mediums is often associated with significant changes in force. Three topics with implications in water-entry are discussed, along with a fourth topic on water-exit. For a plunge-diving seabird, the first two stages of water-entry (initial impact and air-cavity formation) create large stresses on the bird's neck. Linear stability analysis of a cone-beam system impacting water shows buckling and non-buckling behaviors on the beam, which is extended to the diving birds. The next topic is related to the third stage of water-entry (air-cavity pinch-off), in which the chest feathers come in contact with the water. Here, the elasticity of Northern Gannet contour feathers is calculated using the nonlinear bending equation. The third topic will explore the formation of ripples along air cavity walls and their resulting force after pinch-off. An acoustic model predicts the observed wavelengths of the ripples. The final topic will delve into the mechanics of how animals leap out of water. A scaling law that balances the power of thrust and drag will predict the height of the jump. Finally, a bio-inspired robot was built to help identify physical conditions required to jump out of water.

The effects of environmental change on vast, inaccessible marine ecosystems are often difficult to measure and detect. As accessible and highly visible apex predators in marine environments, seabirds are often selected as indicators for studying the effects of disturbance at lower trophic levels, although data are restricted both temporally and spatially. For example, studies of seabirds have historically been limited to the breeding season, with limited data being available throughout the remainder of the annual cycle. Additionally, understanding of habitat associations and behavior of seabirds in the marine environment comes primarily from pelagic seabirds, whose habitat year-round is generally in remote marine areas removed from anthropogenic development, while similar data from nearshore seabirds are less common. Such data gaps limit our understanding or life-history traits among seabirds, one of the most imperiled avian groups globally, and subsequently our ability to inform conservation and marine spatial planning. My goal was to examine ecological relationships of diet, breeding biology, and movement patterns of a nearshore tropical seabird, the Eastern brown pelican, in the Gulf of Mexico, one of the most anthropogenically developed marine ecosystems worldwide. While my results supported previous findings that nutritional conditions are a key driver of seabird reproductive success and recruitment, they differ in suggesting that prey availability and delivery rates are more important to reproductive rates than energetic value of prey species. Since direct measurement of reproductive rates is time-consuming and difficult to collect, I also tested an integrated measure of nutritional stress during development, feather corticosterone, as a predictor of nestling survival and fledging rates. Corticosterone predicted 94% of inter-colony variation in fledging success and was also correlated with post-fledging survival, making it a powerful tool for measuring demographic patterns in this species. To measure adult movement patterns, I deployed bird-borne biologgers to collect highly accurate spatial data from pelicans throughout the annual cycle. I found that individual breeders quickly returned to normal behavior after capture and tagging. GPS tracking also indicated that pelicans were highly mobile, ranging over large areas during the breeding season and migrating up to 2,500 kilometers during non-breeding. Movement patterns were influenced by local conspecific competition during both breeding and migration, such that birds from larger colonies moved longer distances year-round compared to those from smaller colonies. I also found a high degree of spatial, temporal, and individual variation in exposure to surface pollutants across the population. I recorded a high degree of individual variation in movement, which interacted with pollutant exposure to create a complex and varying distribution of risk throughout the northern Gulf metapopulation of brown pelicans. Understanding the factors driving this variation will inform future monitoring, conservation, and mitigation efforts for this species.

The human capacity to expand niche breadth through cultural evolution has propelled humans into keystone ecological roles in many ecosystems. In particular terrestrial animal assemblages have experienced radical reductions in diversity and size distribution. Oceanic habitats have experienced shorter histories of exploitation and typically retain faunal assemblages that more closely resemble pre-human Pleistocene assemblages. Although the direct harvest of many marine mammal and seabird species has diminished in recent decades, these assemblages now face an onslaught of novel human impacts in marine and oceanic island habitats. Stressors range from noise and chemical pollution to the introduction of invasive mammalian predators on oceanic islands. To develop a better understanding of how these disparate effects will impact the ecologies and conservation statuses of wide-ranging, dynamic, and patchy seabird and marine mammal populations, this dissertation leveraged the use of two extensive observational datasets collected by and in collaboration with the NOAA-NMFS Southwest Fisheries Science Center. In the first section (Chapters 1-3) I used satellite tag and biopsy sampling 1) to describe vertical habitat use and biogeographic distribution patterns, and 2) to develop a systematic framework to better understand foraging ecology trade-offs in seven species of toothed whales from the Bahamas. In the second section (Chapters 4-5) I have applied innovative modeling techniques to estimate population abundance and growth rate parameters using an extensive time series of seabird transect surveys. These parameters play critical roles in assessing population status and developing strategic management decisions.

The non-breeding period is a critical life history period for seabirds, as individuals need to regain body condition lost while breeding. Where animals move is driven by a myriad of factors that can be divided into intrinsic factors, which are linked to physiological and life-history traits, and extrinsic factors which occur as the result interactions with other animals or the environment. To better understand the challenges of wintering in the North Pacific marine ecosystem, I studied the migrations and foraging ecology of three species, surface foraging black-legged kittiwakes (Rissa tridactyla) and red-legged kittiwakes (R. brevirostris), and deep-diving thick-billed murres (Uria lomvia) from three colonies in the southeastern Bering Sea. I tracked birds with geolocation loggers and time-depth recorders over three winters with contrasting environmental conditions (2008-2011). Remotely-sensed environmental data was used to highlight the effects of changing conditions both intra- and inter-annually, while stable isotope values of carbon and nitrogen from feather tissue were used to infer dietary trophic level and niche partitioning. In Chapter 1, I contrasted red-legged and black-legged kittiwake wintering ecology across the spatial, behavioral and dietary niche dimensions and found significant partitioning; red-legged kittiwakes showed greater specialization across all niche dimensions and depended almost exclusively upon on the Bering Sea ecosystem. In Chapter 2, I assessed individual winter foraging strategies of thick-billed murres using a combination of spatial, stable isotope, and behavioral data. Both annual and body size differences largely determined strategies, with some larger bodied birds from St Paul using a deeper daytime diving and more residential strategy unexploited by smaller birds. In Chapter 3, I contrasted intrinsic drivers (e.g. sex, breeding colony and experience) with the influence of annual habitat conditions on black-legged kittiwake winter distributions. I found large annual differences in distributions that spanned the sub-arctic North Pacific, yet in consecutive winters individuals returned to the same regions more often than expected. Overall, environmental conditions played a significant role in influencing the movements and behavior of individuals, however life history characteristics in consecutive winters such as sex, dietary preference or body size sometimes constrain individual wintering ecology.

Levels of lead (Pb) and cadmium (Cd) were investigated as potential stressors in adult African penguins (Spheniscus demersus) in the Western Cape Province, South Africa and in nine species of breeding seabirds on Marion Island, South Africa. Seabirds are sentinels of environmental pollution and allow researchers to study contaminant dynamics in marine ecosystems. Many seabirds occupy high trophic positions, which gives them the potential to highlight threats to other apex predators from environmental pollutants. They also accumulate contaminants in higher concentrations because of their greater size and lifespan than may be detectable in lower trophic organisms. Blood samples were collected from African penguins between 2007 and 2011, and from nine species of seabirds on Marion Island in 2011. The whole blood method for graphite furnace atomic absorption spectroscopy was used to analyze samples. In penguins, the majority of blood Pb levels (97%) and blood Cd levels (80%) were within levels considered to be background exposure. Significant differences were observed among colonies, years, and seasons. The Pearson correlation coefficient between Pb and Cd for individual penguins was 0.3149 (p = 0.0005). Marion Island samples revealed individual blood Pb concentrations ranged from 0.80 (king penguin Aptenodytes patagonicus) to 54.89 μg/dL (wandering albatross Diomedea exulans), the majority of blood Pb levels (95%) were below background exposure. Species was a significant factor (p = 0.0005) for mean blood Pb levels, which ranged from 3.62 (dark-mantled sooty albatross Phoebetria fusca) to 14.68 μg/dL (wandering albatross). Fewer individual blood Cd levels (less than 60%) were within background exposure levels. Species was not significant (p = 0.7145). The Pearson correlation coefficient between Pb and Cd was r = 0.3389 (p = 0.0262), and varied by species. Overall, the results suggest Pb and Cd are not a primary cause for concern in these seabirds. This work contributes to a multi-disciplinary ecological risk assessment for the declining population of African penguins and a component of the Seabird Health Survey organized by the Southern African Foundation for the Conservation of Coastal Birds (SANCCOB).

Although wildlife conservation actions have increased globally in both number and complexity, the dearth of scalable, cost-effective monitoring hampers effective intervention to understand conservation efficacy. Automated sensors and computer aided analysis have expanded the tools available for conservation monitoring. For threatened and elusive seabirds, acoustic monitoring presents a cost-effective, scalable alternative to traditional monitoring methods that are limited by remote or inaccessible locations requiring skilled field personnel. A key assumption in monitoring population trends acoustically is that measures of acoustic activity are correlated with the relative nesting abundance of seabirds at colony sites. Here we tested the efficacy of acoustic activity as an index of seabird nesting abundance at colonies. Sensors recorded ambient noise at Forster's Tern (Sterna forsteri) breeding colonies in San Francisco Bay for two breeding seasons. We used an automated method (spectrogram cross-correlation) to detect and count tern advertisement calls from recordings. We calculated mean seasonal call rate and compared it to the mean active nest count at colonies. Our results show that acoustic activity was a reliable index of colony size among breeding sites and an accurate index of change in colony size between years (adj. R2=0.94, n=5, p

Fluctuations of food availability, habitat quality, and environmental conditions throughout the year have been implicated in the breeding success and survival of migratory birds. Levels of circulating corticosterone, the hormone involved in energy balance and the stress response in birds, are also affected by fluctuations in these variables, and also play a role in self-maintenance and survival. In addition to changes in behaviors and resource allocation, the metabolic effects of corticosterone increase the amount of free radicals in the body, which can cause oxidative stress and damage lipids and DNA. In this thesis, I assessed if diet and physiology during the breeding and non-breeding seasons contributed to the reproductive success, survival, and oxidative stress of a long-lived migratory seabird, Leach’s storm-petrel (Oceanodroma leucorhoa). I tested the hypotheses that 1.) diet and physiology throughout the breeding and non-breeding seasons predict reproductive effort; and 2.) corticosterone affects telomere length, a measure of oxidative damage. Through analyses of stable isotopes, corticosterone, and antioxidant capacity, I found that although there was variation in these measures of diet and physiology within the population, none of these factors during the breeding or non-breeding seasons correlated with reproductive effort or success. I also found that feather and plasma corticosterone did not predict telomere length. The life history strategies of Leach’s storm-petrels appear to be complex, and many factors likely contribute to self-maintenance and the decision to breed. Long-term monitoring of these variables may help identify relationships between trends in oceanographic variables during both the breeding and non-breeding seasons with reproductive effort and success, and survival.

The peer attraction hypothesis states that the stimuli associated with an active seabird colony attract individuals to a breeding site. To test this hypothesis I observed the response of two species of colonial seabirds to experimentally simulated colonies. The artificial colonies consisted of models of courting birds and recordings of courtship calls. Laysan Albatrosses land more frequently and spend more time in areas containing models of courting albatrosses than in areas without models. Within the experimental areas containing models, albatrosses are closer to the models than predicted assuming a random pattern of distribution. The response of albatrosses to different model types is non-random. Albatrosses are attracted to three dimensional models over two dimensional models and to pairs of models over single models. The capture rate of Leach's Storm-petrels in mist nets is greater when tape recordings of both the flight and underground courtship vocalizations are presented in conjunction with artificial burrows than when either vocalization is presented alone. Leach's Storm-petrels colonize artificial burrows that have taped courtship vocalizations playing from a central location but fail to colonize burrows not stimulated with sound. Colonization is found to be more likely when both courtship vocalizations are presented than when either vocalization is presented alone. Storm-petrels colonize burrows that are closer to the speakers than would be expected from a random pattern of colonization. Both visual and auditory courtship displays are found to function in the breeding site selection of these two species. These data are explained in light of the evolutionary advantage to colonial breeding in seabirds and are used to support the peer attraction hypothesis for colony formation in colonial birds. This research has implications for the management and potential recovery of endangered colonial birds. If individuals could be attracted away from deteriorating sites and encouraged to colonize those which remain viable, recovery may be possible.