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Browsing by Author "Doherty, Paul F., Jr., committee member"

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    Factors influencing breeding avifauna abundance and habitat selection in the alpine ecosystem of Colorado
    (Colorado State University. Libraries, 2017) Spear, Shelley Laine, author; Aldridge, Cameron L., advisor; Skagen, Susan K., committee member; Doherty, Paul F., Jr., committee member
    Species in alpine habitat occupy high elevation areas with limited scope for upslope migration, and as a result are expected to react sensitively to climate-caused habitat alteration. Changes in temperature are causing an advancement of treeline and rearrangement of habitat and species distributions. Alpine birds in particular are predicted to be impacted by climate change, especially species that breed in and are endemic to this ecosystem. In order to understand just how sensitively alpine birds will respond if their habitat structure is altered by climate change, determining the fine-scale mechanisms driving their current relationships with alpine habitat is important. In Chapter 1, I discuss some of the relationships between birds and their surrounding environment and the importance of understanding these species-habitat interactions. I introduce the alpine breeding focal species and how some of these avian species have exhibited population declines in Colorado. I also present my research objectives that aimed to understand breeding avifauna abundance in relation to fine-scale habitat features (Chapter 2), and how specific habitat characteristics drive important breeding site selection for an alpine endemic species (Chapter 3). Chapters 2 and 3 (described below) are data chapters written in a format to be submitted for journal publications. In Chapter 2, I test how fine-scale habitat and environmental characteristics influence abundance of avian species breeding in Colorado's alpine ecosystem. I provide results on how abundance and occurrence of these breeding species were influenced by abiotic, biotic, anthropogenic, temporal, and spatial factors in the alpine. Biotic components affected the abundance of all three of the breeding birds that we modeled using count data; American pipit (Anthus rubescens), horned lark (Eremophila alpestris), and white-crowned sparrow (Zonotrichia leucophrys oriantha). However, abiotic, anthropogenic, spatial and temporal factors also contributed to their abundance and occurrence. Knowing which fine-scale factors influence these alpine species' abundance the most, will allow us to prioritize conservation efforts for each particular species, and improve our ability to predict how their abundance will change if alpine habitat is altered in response to climate change. In Chapter 3, I ask how fine-scale habitat and environmental characteristics influence nest and brood-site selection by breeding white-tailed ptarmigan (Lagopus leucura) in Colorado's alpine. I conducted analyses across multiple spatial scales: patch and site level, at nesting and brood-rearing sites. Forage resources and protective cover were the prominent features driving selection at these two alpine sites during both breeding periods. Specifically, nest site selection at the patch scale was more influenced by percent cover of forage forbs, rock and gravel, and shrubs and willows. However, at the site scale, we found hens selected nest sites when percentage of graminoid cover was less and elevations were lower. Hens selected brood sites at the patch scale that were in closer proximity to willows and shrubs and that had rock and gravel cover to a particular threshold. A subset of our brood data indicated brood site selection was driven by abundance of insects over vegetation components. In this chapter, I highlighted the dependence on forage quantity and protective cover across two ptarmigan breeding stages, as well as differences among scales. These findings demonstrated the importance of considering a spatial resolution with a temporal aspect (i.e., different breeding stages) in resource selection studies especially when habitat covariates are collected at fine spatial scales. With all aspects of this research, I discuss in each chapter how conducting additional and longer-term studies on a fine-scale basis helps to not only establish further alpine breeding bird-habitat relationships in these areas, but in identifying if populations are stable, and if and when they respond to changes in habitat structure. Furthermore, in my final section, Chapter 4, I suggest analyzing these relationships across a larger extent and propose how a landscape-scale analysis can be applied to breeding bird species-habitat relationships in the future to determine at what scale these species could respond if climate change impacts their alpine habitat.
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    Nonparametric tests for informative selection and small area estimation for reconciling survey estimates
    (Colorado State University. Libraries, 2020) Liu, Teng, author; Breidt, F. Jay, advisor; Wang, Haonan, committee member; Estep, Donald J., committee member; Doherty, Paul F., Jr., committee member
    Two topics in the analysis of complex survey data are addressed: testing for informative selection and addressing temporal discontinuities due to survey redesign. Informative selection, in which the distribution of response variables given that they are sampled is different from their distribution in the population, is pervasive in modern complex surveys. Failing to take such informativeness into account could produce severe inferential errors, such as biased parameter estimators, wrong coverage rates of confidence intervals, incorrect test statistics, and erroneous conclusions. While several parametric procedures exist to test for informative selection in the survey design, it is often hard to check the parametric assumptions on which those procedures are based. We propose two classes of nonparametric tests for informative selection, each motivated by a nonparametric test for two independent samples. The first nonparametric class generalizes classic two-sample tests that compare empirical cumulative distribution functions, including Kolmogorov–Smirnov and Cramér–von Mises, by comparing weighted and unweighted empirical cumulative distribution functions. The second nonparametric class adapts two-sample tests that compare distributions based on the maximum mean discrepancy to the setting of weighted and unweighted distributions. The asymptotic distributions of both test statistics are established under the null hypothesis of noninformative selection. Simulation results demonstrate the usefulness of the asymptotic approximations, and show that our tests have competitive power with parametric tests in a correctly specified parametric setting while achieving greater power in misspecified scenarios. Many surveys face the problem of comparing estimates obtained with different methodology, including differences in frames, measurement instruments, and modes of delivery. Differences may exist within the same survey; for example, multi-mode surveys are increasingly common. Further, it is inevitable that surveys need to be redesigned from time to time. Major redesign of survey processes could affect survey estimates systematically, and it is important to quantify and adjust for such discontinuities between the designs to ensure comparability of estimates over time. We propose a small area estimation approach to reconcile two sets of survey estimates, and apply it to two surveys in the Marine Recreational Information Program (MRIP). We develop a log-normal model for the estimates from the two surveys, accounting for temporal dynamics through regression on population size and state-by-wave seasonal factors, and accounting in part for changing coverage properties through regression on wireless telephone penetration. Using the estimated design variances, we develop a regression model that is analytically consistent with the log-normal mean model. We use the modeled design variances in a Fay-Herriot small area estimation procedure to obtain empirical best linear unbiased predictors of the reconciled effort estimates for all states and waves, and provide an asymptotically valid mean square error approximation.
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    Provisioning and nest success of an aerial insectivore at a high elevation breeding site
    (Colorado State University. Libraries, 2023) Simons, Victoria F., author; Horton, Kyle G., advisor; Doherty, Paul F., Jr., committee member; Ruegg, Kristen C., committee member
    Tree Swallows (Tachycineta bicolor) are a model organism in ornithology. However, few studies have been conducted in the western portion of their breeding range, particularly at high elevation. High elevation habitats, like Colorado State University's Mountain Campus, are impacted by climate change. Tree Swallows in these ecosystems face threats due to recent population declines and climate-related changes. These challenges could impact the species' survival in these areas, and for my Master's thesis I investigated two aspects of provisioning behavior, namely weather conditions and insect abundance. My first chapter focused on how daily weather conditions influenced female Tree Swallow's rates of nest visitation and food provisioning. Using radio-frequency identification technology, I compared visitation rates to hourly weather conditions. I found that poor weather, including cooler temperatures and precipitation events, was negatively correlated with the number of visits made to the nest, which subsequently influenced the growth and development of nestlings. In Chapter 2, I addressed the question of how weather affected food availability. Tree Swallows rely on flying insects as their main food source, and inclement weather is known to decrease insect availability in the airspace. To investigate if lowered female provisioning effort matched periods of food unavailability, I deployed a mobile radar unit – the BirdScan MR1 – to quantify insect abundance. I then compared insect activity to nest visitation rates and found that females made significantly more visits to their nestlings when insects were more abundant. Additionally, I found that insect activity was significantly influenced by weather conditions, demonstrating that weather may be used as a proxy for insect abundance at sites where direct monitoring of insects is not possible. Put together, the results of my first and second chapters deepen our understanding of how female Tree Swallows navigate the complexities of aerial conditions – both biotic and abiotic – to forage and provision for their growing nestlings in an ever-changing high elevation environment. As the effects of climate change become more pronounced, high elevation habitats are likely to undergo rapid changes. Consequently, insight into the relationship between weather and food availability becomes increasingly important.