Competition is one of the most important biotic interactions influencing animal communities and species distributions. In the Central Valley of California, several species of waterfowl compete for space and food during winter. Goose populations are increasing in California and the Pacific Flyway and are now at levels well above population targets. The growing numbers of geese may have negative impacts on smaller-bodied members of the Anatidae family. To evaluate the potential of this growing conflict, we used high frequency GPS-GSM telemetry to track 211 individuals of four species of geese: the Lesser Snow goose (Anser caerulescens caerulescens), Ross’s goose (Anser rossii), Pacific White-fronted goose (Anser albifrons sponsa), and Tule White-fronted Goose (Anser albifrons elgasi; hereafter referred to as Tule goose) across the Sacramento Valley (the northern portion of the Central Valley) of California. Using step selection analyses, we modeled how field type, photo period (day or night), habitat condition (wet or dry) and age of those habitat conditions impact goose use and habitat selection. All species showed a strong preference for wet rice habitat at night, but daytime preferences varied. Lesser Snow and Pacific White-fronted geese were most similar, selecting wet fallow and dry rice habitats over wet rice and dry fallow during the day. Conversely, California species of concern, Tule geese, strongly preferred wetlands while Ross’s geese preferred dry rice, followed by wet and dry fallow habitats. Habitat age was important and the preference for wet rice and wetlands decreased over time, while selection of dry rice and wet fallow generally increased with age. Due to agricultural flood regimes, wet rice habitats likely offer substantial quantities of nutrient dense food resources to arriving migratory birds. However, over time, heavy consumption and decomposition caused by water cover reduces the attractiveness of this habitat, coinciding with the period which birds often switch to green browsing in other habitats.

Reproduction is perhaps one of the most energetically expensive activities that an individual performs in a lifetime. Many species have evolved behaviors and tactics to offset the energetic and physiological costs of reproduction while optimizing long-term reproductive success and survival. Some individuals do so by parasitizing the reproductive efforts of other individuals, thereby reducing the costs of reproduction while still maintaining some reproductive output. Conspecific brood parasitism (CBP) is one such alternative reproductive tactic whereby some females lay eggs in the nests of females of the same species to avoid the cost of rearing and caring for those offspring. The evolution of this behavior has received considerable theoretical attention, but surprisingly there have been few quantitative studies examining the interactions between parasitic females and the host of the nest. We used motion sensor cameras and radio frequency identification devices to record the behavior interactions at the nest among female wood ducks (Aix sponsa) in a population in California. Our observations revealed a remarkable range of responses in female-female interactions. We classified females as “owners” if they incubated the nest and as “intruders” if they entered the nest, potentially laid eggs but did not incubate the nest. There were significant differences in behavior and variation of response for owners and intruders; intruders typically exhibited passive, nonaggressive behaviors and avoided interactions with the owner, while owners often behaved aggressively, although they also showed a wider variation in response. Repeatability (measured as the interclass correlation coefficient) of female behavior was significant and high for owners, but low among intruders. We tested several hypotheses on the possible factors that might account for variation in responsiveness, including the effects of status, age/experience, body size/phenotype/resource holding potential, history with the nest/previous ownership, and nest site timing. Status had a strong influence on all behavioral dynamics. Absolute age and body weight/condition did not influence the level of response, but relative differences in age and body weight/condition between owners and intruders had a strong effect. Owners were increasingly more aggressive when they were relatively older or larger than a given intruder. However, these same relative differences in age and size did not affect the behavioral response of intruders. Owners were also more aggressive to intruders during incubation than during the egg-laying period. There was no effect of previous history of the female or use of the box. Intruders laid an egg during 37 of the 57 observed encounters with owners, indicating that the intruders were, in at least most cases, acting as brood parasites. Owner aggressiveness did not prevent intruders from laying an egg. The passive avoidance of intruders in all interactions suggests strongly that these were parasitic interactions and not simply instances of two females fighting for possession of a nest site. The variation in the observed level of aggressiveness among pairs of females is intriguing and suggest that owners may act differently to some females; future research will explore the pattern of kinship and social relationships among these females.

Effects of climatic change are observed to be rapidly increasing, particularly in northern latitudes. Some of the results of climate change include increased climatic stochasticity, which results in high inter-annual variability in the timing of spring onset. Migratory species that rely on these northern climates may be impacted disproportionately by these changes because they utilize networks of diverse habitats over a large area that are experiencing different rates and effects of climate variability. However, short-distance migrants like the Common Goldeneye (Bucephala clangula) may be better able to track phenological changes due to similarities in climate conditions on wintering and breeding grounds. I used a long-term dataset (1997-2020) of Common Goldeneye nesting records from interior Alaska, near the northern extent of the species’ range, to examine the impacts of changing spring phenology on reproductive ecology. I used nesting initiation date as an indicator of breeding phenology and examined how nest initiation date varied over the 23-year study period. I then evaluated the influence of predictor variables related to spring conditions, winter conditions, female body condition, and known breeding experience on nest initiation date. Finally, I examined trends in female body condition during the study period and examined the relationship of body condition to winter conditions and known breeding experience. Across all analyses, my results indicated that nest initiation dates varied significantly with measures of spring phenology, wintering area conditions, body condition, and previous breeding. Model estimates indicate that the mean nest initiation date for this population is advancing at 0.71 days per year. Unexpectedly, poorer body condition was correlated with warmer winter conditions, which may result in future impacts on reproductive output as climate change advances. Model results also demonstrated high repeatability of individual females as a random effect, meaning that females may consistently respond to climatic conditions independently from other females, suggesting that female personality may influence phenological responses. Though goldeneyes appear to currently track the advancement of spring conditions, my results suggest that these migratory birds rely on multiple signals to determine timing of nesting, and uncertainty remains as to how these signals may interact to influence breeding phenology in the future.

Individuals within a species or population vary considerably in morphology and behavior. For many species, the specific drivers of variation in these phenotypic traits and their influence on individual fitness are poorly known. In this study, we hatched and reared wood ducks (Aix sponsa) in a captive common garden environment and then released them into the wild shortly after fledging age. For each individual, we evaluated metrics of size, growth, and behavior across ontogeny to determine whether individuals vary in morphological and behavioral traits when raised in a controlled captive setting. These individuals (n = 106 females) were then released into wild study populations where we tracked first year survival and multiple longer-term measures of fitness through standard monitoring methods and radio frequency identification. Using multivariate statistics and generalized linear models, we analyzed early life variation in morphology and behavior and their influence on individual fitness. Despite identical rearing conditions, we found considerable inter-individual variation in both morphological and behavioral traits. Additionally, we found correlations among egg size, hatch size, and fledging size, although maximum growth rate was the strongest predictor of fledging size. Contrary to evidence in the literature, we found no indication that morphological traits had any influence on first year survival; however, there was some evidence that survival was positively influenced by tonic alertness. We found evidence that both morphology and behavior were influential in multiple measures of long-term success. Here, our strongest results showed a negative relationship between initial size and longevity, and a positive relationship between tonic alertness and number of years incubating. The results of this study shed new light on the development of phenotypic variation in precocial birds and its consequences for individual fitness, and provides insight for captive breeding programs and conservation efforts.

Wetland conservation in California faces a multitude of challenges, this is especially true in the Suisun Marsh, one of the largest tidal marshes on the west coast of North America. The marsh has historically supported large numbers of non-breeding waterfowl but the capacity of the marsh to continue to do so remains uncertain, due to drought, habitat loss, future sea level rise, and conflicting conservation needs for many species of fish and wildlife. A guiding principle for the conservation of non-breeding waterfowl is to manage for food resources, under the working hypothesis that food resources may be limiting in winter, and the decline in the abundance of waterfowl within Suisun Marsh may be due to reduced food production or availability. Non-breeding waterfowl depend on plant seeds as a primary source of food throughout winter. However, we lack information concerning what food resources may be in limited supply because there has never been a direct assessment of total seed abundance in Suisun Marsh. Efforts to recover threatened and endangered species within the marsh – through the conversion of managed wetlands to tidal marsh ¬– could further impact the carrying capacity of the marsh for waterfowl by reducing the abundance or availability of waterfowl food resources. To evaluate these concerns, I undertook a multifaceted study to evaluate the abundance, production, and depletion of food resources for wintering waterfowl in both tidal and managed wetlands. I found that seed abundance in both wetland types was much lower than previously predicted. Seed abundance in Fall was similar in tidal (172.9 kg/ha) and managed (163.8 kg/ha) wetlands, but there was considerable spatial variation. The species composition of seeds differed substantially according to wetland type; over 75% of aggregate seed mass in managed wetlands was comprised of food species that waterfowl prefer, while a non-preferred food, Schoenoplecutus sp., was the dominant seed in tidal marshes. The occurrence of several plant species within managed wetlands that produce waterfowl-preferred seeds was correlated with salinity, wetland management intensity, and disking. The best predictor of total seed abundance in managed wetlands was habitat zone, which is defined by shared physical factors known to impact vegetation growth and production in different regions in the marsh. These regional differences in seed abundance have important implications for tidal restoration efforts, as the loss of seasonal wetland acreage within more productive regions could have a disproportionate impact on total food availability. To evaluate seed dynamics at a finer scale, I used small-scale sampling sites and foraging exclosures in a managed wetland within the marsh and stratified these sampling locations according to high and low waterfowl use areas. Contrary to expectations of a “table-is-set” hypothesis, I found seed that abundance increased over three weeks post-flooding, and over seven to ten weeks in foraging exclosures. Observed declines in the abundance of seeds were substantially greater than rates of decomposition, suggesting seed removal by waterfowl was a major source of seed depletion. However, the amount of seed consumption that could be attributed to waterfowl was spatially variable and correlated with waterfowl locations – high use areas exhibited significantly higher rates of seed loss. Hydrochory (movement of seed due to water flow) was likely responsible for the changes in seed abundance observed for several weeks after the wetlands were flooded, as abundances within foraging exclosures nearly tripled over ten weeks in high waterfowl use areas. These results suggest that seed removal by waterfowl and hydrochory can impact our ability to accurately estimate peak seed abundance. Without accounting for seed removal by waterfowl, and hydrochory, bioenergetic models may produce inaccurate estimates of habitat carrying capacity. My results provide new insight and greater refinement of estimates of seed abundance to more accurately determine the carrying capacity of the Suisun Marsh for wintering waterfowl, and to assess the potential impacts of future changes.