Browsing by Author "Horton, Kyle G., advisor"

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Open Access
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.
Embargo
Response of roosting aerial insectivores to ongoing climate change quantified by weather surveillance radar
(Colorado State University. Libraries, 2025) Deng, Yuting, author; Horton, Kyle G., advisor; Bailey, Larissa, committee member; Kendall, William, committee member; Ruegg, Kristen, committee member
Aerial biotas encompass species that feed on airborne insects while in flight, including various bird species (e.g., swallows, martins, nightjars, and flycatchers), bats, and insects (e.g., dragonflies). This community inhabits aerial habitats and occupies a critical interface between terrestrial and aquatic ecosystems. Because these ecosystems provide essential food resources and habitats, aerial insectivores' responses to climate change are closely tied to shifts at these ecological boundaries. As climate change intensifies, these habitats are increasingly unpredictable due to long-term climate shifts and more frequent extreme weather events, like cold snaps. These environmental changes may have driven biological changes at varying levels across aerial trophic food webs, potentially leading to trophic mismatches—where the timing of consumer demand no longer aligns with the availability of their food resources. As a result, aerial insectivores are particularly vulnerable to these shifts, and many are experiencing acute population declines. As key predators in the aerial trophic system, aerial insectivores help maintain ecosystem balance and health. They also provide ecosystem services, such as pest population control and the reduction of insect-borne diseases. Despite their ecological and agricultural importance, knowledge gaps remain regarding how aerial insectivores respond to environmental changes at a macrosystem scale—particularly regarding shifts in phenology and population dynamics. Addressing this knowledge gap is crucial for understanding and mitigating the cascading effects of these changes on ecosystems. Therefore, there is a need to monitor changes in aerial insectivore populations and phenology. In North America, some aerial insectivore species form large roosting aggregations—sometimes numbering in tens of thousands—during certain life cycle stages. These roosts appear on Next Generation Weather Radars (NEXRAD) as expanding "angel rings," providing a unique opportunity to quantify their occurrence across broad spatial and temporal scales. To leverage this, I integrated decades of radar data with other remote sensing datasets and machine learning tools to quantify phenological and population changes and to investigate their drivers in two taxonomic groups of roosting aerial insectivores: swallows and bats. My dissertation centers around the key question: How has the phenology and population of these aerial insectivores changed in response to changing climate? To address this, I first focused on roosting swallows in the Great Lakes region, primarily Tree Swallows and Purple Martins. Chapter 1 asks How swallow roosting phenology changed over the past two decades? Chapter 2 asks Which aspects of climate change, during which periods, at what locations, impact swallow roosting phenology at the Great Lakes? In Chapters 3 and 4, I shifted my focus to Mexican free-tailed bats in south-central Texas. Chapter 3 asks Has phenology and population of Mexican free-tailed bats changed in this region? Chapter 4 asks Can I predict the intensity of nightly emergence events of Mexican free-tailed bats? The goal of my work is to provide ecological evidence of these changes and uncover the underlying mechanisms, offering insights that can inform conservation policies and actions.
Open Access
Spatial and temporal patterns of abundance of swallow and martin communal roosts
(Colorado State University. Libraries, 2025) Belotti, Maria Carolina Tiburcio Dias, author; Horton, Kyle G., advisor; Bailey, Larissa, committee member; Koons, David, committee member; Ross, Matthew, committee member
During their non-breeding period, many species of swallows and martins (family: Hirundinidae) congregate in large communal roosts, which can gather hundreds of thousands of individuals. These roosts are well-known within local birdwatching communities; however, monitoring them at large spatial scales and with day-to-day temporal resolution is challenging. Due to the high densities of birds within these aggregations, however, their early morning dispersals can be systematically detected by nearby weather radars, which can be used to collect data about roost timing, size, and location. Nonetheless, finding roost signatures amongst the millions of rendered reflectivity images is extremely time-consuming — a fact that has limited the spatial and temporal scopes of previous radar-based studies. We leveraged the recent advances in computer vision and high-performance computing to partially automate this task and build a dataset of 22 years of roost detections captured by 12 radar stations in the Great Lakes region. We first verified that these detections correspond to swallow and martin roost dispersals, comparing the phenology of our findings with that obtained from eBird data. We then describe changes in the roost size distribution throughout the season and discuss the relationship between a roost's size and its persistence in the landscape. We also obtained trends of roost activity, comparing those with breeding population trends from eBird and the North American Breeding Bird Survey. Lastly, we used two years of data (2014-2015) collected by an operational weather radar in Manaus to describe, for the first time, the phenology of swallow and martin aggregations in the Low Negro-Solimões region of the Amazon Rainforest. We compared roosting behavior in the Amazon with what we observed 6,000 km away, in the Great Lakes region, regarding the daily number of birds and the roost size distribution. Our work demonstrates how weather radars offer us a unique opportunity to monitor and study swallow and martin populations at an unprecedented transcontinental scale, something that can rarely be achieved for any other taxa.