Urban Naturalist Volume 13, 2026 Urban Naturalist No. 87 Connecting Great Horned Owl (Bubo virginianus) Space Use and Diet in an Urban Park Arina Martin, Stephen Blake, Sharon L. Deem, Jeffrey Meshach, Jamie Palmer, Anthony Dell, August Wise, Avery Valenciano, and Stella F. Uiterwaal Urban Naturalist The Urban Naturalist (ISSN # 2328-8965) is published by the Eagle Hill Institute, PO Box 9, 59 Eagle Hill Road, Steuben, ME 04680- 0009. Phone 207-546-2821 Ext. 4. E-mail: office@eaglehill.us. Webpage: http://www.eaglehill.us/urna. Copyright © 2026, all rights reserved. Published on an article by article basis. Special issue proposals are welcome. The Urban Naturalist is an open access journal. Authors: Submission guidelines are available at http://www.eaglehill.us/urna. Co-published journals: The Northeastern Naturalist, Southeastern Naturalist, Caribbean Naturalist, and Eastern Paleontologist, each with a separate Board of Editors. 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Instructions for Authors are available online on the journal’s website (http://www.eaglehill.us/urna). ♦ It is co-published with the Northeastern Naturalist, Southeastern Naturalist, Caribbean Naturalist, Eastern Paleontologist, Journal of the North Atlantic, and other journals. ♦ It is available online in full-text version on the journal's website (http://www.eaglehill.us/urna). Arrangements for inclusion in other databases are being pursued. Cover Photograph: Adult female Great Horned Owl (nicknamed Astrid) and her chick in Forest Park, Saint Louis Missouri. Photo taken by Dr. Stephen Blake. Urban Naturalist A. Martin et al. 2026 No. 87 1 2026 Urban Naturalist 87:1–14 Connecting Great Horned Owl (Bubo virginianus) Space Use and Diet in an Urban Park Arina Martin1,2*, Stephen Blake2,3, Sharon L. Deem4, Jeffrey Meshach5, Jamie Palmer4, Anthony Dell6,7, August Wise2,8, Avery Valenciano2,9, and Stella F. Uiterwaal2,4,6,7,10 Abstract – With increasing urbanization, many raptor species have readily adjusted to living in urban areas. However, raptors continue to face significant anthropogenic threats that result in high rates of morbidity and mortality. Great Horned Owls (Bubo virginianus) occur in cities across the United States, yet few studies have documented their ecology in urban areas. Here, we investigated the health, diet, movement, and activity of one female Great Horned Owl in Forest Park, Saint Louis, Missouri, one of the largest urban parks in the United States. We used GPS and accelerometry data combined with pellet analysis to examine how this owl used an oasis of green space within a densely developed urban landscape. We describe patterns in space use, demonstrating widespread use of developed areas both inside and outside of the park, and show increased use of areas outside of park boundaries in months with higher space use. We compare dietary data with those of other urban and rural Great Horned Owls, show seasonal variation in diet, and identify correlations between movement, diet, and temperature, suggesting variable energetic demands and intake throughout the annual cycle. Lastly, we provide detailed health information on this healthy and reproductively active female owl to complement our current understanding of baseline health values for Great Horned Owls in urban settings. These findings offer a uniquely detailed insight into how one Great Horned Owl exploited an urban landscape, providing novel data on the ecological trade-offs that may confront urban raptors to help inform planning for raptor conservation in urban green spaces. Introduction As habitat and dietary generalists, Bubo virginianus Gmelin (Great Horned Owls) are widespread across North and South America. These owls are predominantly sedentary, with very few individuals demonstrating other movement strategies (Holt Jr 1996, Rohner 1997). Great Horned Owls frequently nest in urban parks and suburban areas (Bennet and Bloom 2005, Bosakowski and Smith 1997, Holt Jr 1996, Lambert 1981, Rullman and Marzluff 2014, Smith et al. 1999), and while few studies have stated explicitly that Great Horned Owls also roost in urban areas, this behavior is suggested in many 1Oregon State University Department of Integrative Biology, 3029 Cordley Hall, 2701 SW Campus Way, Corvallis, OR, USA, 97331. 2Saint Louis University Department of Biology, 3507 Laclede Ave, St. Louis, MO, USA, 63103. 3Max Planck Institute of Animal Behavior, Am Obstberg 1, 78315 Radolfzell am Bodensee, Germany. 4Saint Louis Zoo Institute for Conservation Medicine, 1 Government Drive, St. Louis, MO, USA, 63110. 5World Bird Sanctuary, 125 Bald Eagle Ridge Road, Valley Park, MO, USA, 63088. 6Living Earth Collaborative, Washington University in St. Louis, 1 Brookings Drive, Campus Box 1137, St. Louis, MO, USA, 63130. 7National Great Rivers Research and Education Center, Lewis and Clark Community College, 1 Confluence Way, East Alton, IL, USA, 62024. 8National Audubon Society, Upper Mississippi Regional Office, 301 Riverlands Way, West Alton, MO, USA, 63386. 9Kansas State University College of Veterinary Medicine, 1800 Denison Ave, Manhattan, KS, USA, 66506. 10Center for Conservation Technology and Innovation, Smithsonian Conservation Biology Institute, 1500 Remount Rd, Front Royal, VA, USA, 22630. *Corresponding author: martarin@oregonstate.edu. Associate Editor: Jose Ramirez-Garofalo, Rutgers University. Urban Naturalist A. Martin et al. 2026 No. 87 2 studies, e.g. Hindmarch and Elliott (2015). As such, urban Great Horned Owls may be entirely reliant on heavily modified landscapes throughout the year. Predator use of urban environments is highly dependent on resource availability. Urban areas can contain a higher biomass of potential prey items than rural habitats (Rullman and Marzluff 2014) and competition with other predators may be more limited (Dwyer et al. 2018, Hager 2009). Despite the potential benefits of living in cities, urban raptors also face increased anthropogenic threats from building and vehicle collisions, rodenticide poisonings, and electrocutions (Deem et al. 1998, Hager 2009, Murray and Sánchez 2021). In fact, as large raptors, Great Horned Owls may be particularly vulnerable to human-wildlife conflicts (Washburn et al. 2025). Zoonotic diseases such as avian influenza, avian pox, and trichomonosis are additional threats to urban raptors since city habitats can serve as reservoirs for pathogens. These diseases are often spread through stagnant water that serves as breeding grounds for infectious agents and through other infected wildlife that serve as easy prey for raptors (Boal et al. 1998, Dwyer et al. 2018). Despite these threats increasing with rapid urbanization, the foraging habits of urban raptors are not well understood. While the diets of Great Horned Owls in rural North America have historically been well-documented (Bogiatto et al. 2003, Marti and Kochert 1996, Wink et al. 1987, Zimmerman et al. 1996), less attention has been directed to how their diets vary across environmental gradients, particularly within urban habitats (Hindmarch and Elliott 2015, Kopij 2016). Urbanization is known to alter the diet composition of many species (Gámez et al. 2022, Scholz et al. 2025), signaling a need to better understand the diets of urban raptors. The presence of raptors in cities also suggests the potential for these environments to sustain multiple trophic levels, especially since Great Horned Owls are also known to engage in intraguild predation by preying on smaller raptors (Hindmarch and Elliott 2015, Washburn et al. 2025). Thus, understanding how these predators forage in cities will help to improve our understanding of the ecological health of urban ecosystems. Foraging is also tightly linked to energetics: prey intake provides energy for growth, maintenance, and reproduction, but foraging behaviors such as movement also require energy expenditure (Brown et al. 2004, Potter et al. 2018). Temperature is known to alter energetic demands and foraging behavior through its effects on metabolic rate, often displaying a unimodal relationship characterized by an optimum temperature (Sentis et al. 2012, Uiterwaal and Delong 2020). In urban environments, temperatures can often exceed those of rural habitats due to “heat island” effects (Jabbar et al. 2023, Szulkin et al. 2020). As such, urban predators may experience temperatures substantially above their optima, increasing their energetic demands. Certain species behaviorally compensate for these increased urban temperatures (Johnson et al. 2019, Saikumari et al. 2025), but these relationships have not been empirically documented in Great Horned Owls. Tri-axial acceleration (or activity) is a commonly used metric of energy expenditure (Hernández-Pliego et al. 2017) and when paired with data on movement, prey intake, and environmental conditions, can identify key patterns contributing to the energetic trade-offs of predators. With this focused study, we aimed to begin addressing these knowledge gaps by examining the health, movement, activity, and diet of one urban Great Horned Owl over a full annual cycle. We used a combination of clinical and laboratory health diagnostics, GPS telemetry, triaxial accelerometry, and pellet analysis to evaluate relationships between the health, movement, activity, and diet of this urban Great Horned Owl. We further explored the connection between foraging and energetics, hypothesizing that activity, movement, and diet metrics would be correlated with each other and with Urban Naturalist A. Martin et al. 2026 No. 87 3 temperature, reflecting their inherent biological relationships. Although our study was restricted to a single individual, the integration of multiple data types offers novel insights for ecologists and habitat managers and provides a template for future studies. Methods Study area Forest Park is a large urban park located in Saint Louis, Missouri, USA (38.639, -90.284) which is visited annually by over 15.5 million people (Forest Park Forever 2025). The 526-hectare park contains nearly 78.5 ha of restored forests, woodlands, tall grass prairies, and a reconstructed river system. Great Horned Owls are year-round residents in the park, and although their abundance and distribution are not known, they are known to both roost and nest within the park and adjacent urban areas. In 2020, we identified the roost of a pair of Great Horned Owls near Klein Prairie, located on the eastern edge of Forest Park near a major metropolitan area and hospital (Fig. 1). The roost was located within a cluster of non-native Pinus strobus L. (Eastern White Pine) near a river boardwalk between a large highway to the east and 3.6 ha of restored prairie to the west. Anthropogenic noise and light pollution from the adjacent highway and hospital is prominent; including sirens, low-flying helicopters, vehicle traffic, streetlamps, and hospital lights. Tagging and tracking We captured the female of the pair of Great Horned Owls on the evening of 25 October 2021 with the approval of the Saint Louis Zoo Institutional Animal Care and Use Committee and Wild Bird Sanctuary Station Permit 21110. We used a bal-chatri trap baited with two live pigeons (Bloom et al. 2007). The owl was handled for less than 60 minutes for physical examination, placement of a telemetry backpack, and sample collection using standard raptor handling techniques (Arent and Martell 1996). The backpack consisted of an e-OBS GmbH (Munich, Germany) telemetry tag (Bird Battery 1AA) equipped with a UHF beacon, Figure 1. 95% (yellow) and 50% (red) AKDE home ranges of the female Great Horned Owl with the southeastern boundary of Forest Park, Saint Louis, Missouri indicated by a dashed line. The smaller inset map shows the urban coverage of Saint Louis city surrounding the park. Urban Naturalist A. Martin et al. 2026 No. 87 4 fastened using Teflon ribbon and aluminum crimps. We programmed the tag to collect a burst of tri-axial accelerometer data every two minutes and a GPS location every 2 hours. The owl showed fidelity to her roosting site, facilitating the remote downloading of data from the tag using a handheld receiver approximately every 2 weeks. Estimated battery life for the telemetry tag was 2 years at the programmed settings. Health data collection and analysis We measured body mass to the nearest gram using a Pesola Spring scale (Pesola AG, Schindellegi, Switzerland). We assigned a 0–5 body score (0 = severely emaciated, 3 = ideal, 5 = obese) based on the condition of the pectoral muscles, presence of subcutaneous body fat, and overall condition (Scott 2021). We conducted a full physical exam to identify any abnormalities or damage and to check for the presence of ectoparasites, which were collected and preserved in 70% ethanol. We collected 2.0 mL of blood from the medial metatarsal vein using a 23-gauge needle and 3 mL syringe. Blood was kept in a cooler in the field and then at -20 °C overnight. In the laboratory, we determined packed cell volume (PCV) using microhematocrit tubes and plasma total solids using a temperature-compensated optical refractometer (Deem et al. 2012). In addition, we estimated white blood cell (WBC) counts and performed a manual differential by counting number of WBCs and calculating relative and absolute values for each WBC type (Deem et al. 2012). PCV and WBC counts and differentials are informative of general health status, with PCV providing information regarding potential anemia and WBC counts with differentials informing of possible acute and/or chronic infections. Remaining blood was sent to the Midwest Veterinary Laboratory (Saint Louis, Missouri) for a complete blood count (CBC) with differential and basic metabolic panel and to Bird Sexing Solutions (Antelope, California) for sex determination. Pellet collection and processing We collected a total of 210 pellets from below the roost approximately once a week between October 2021–September 2022. Great Horned Owls usually produce 1 pellet per day (Graber 1962, Marti 1973); however, we note that 2 owls used the roost, the tagged female and her mate. Therefore, pellets collected could have been produced by either individual. Before dissection, we recorded the dry weight, length, and width of fully intact pellets. We also collected intact cranial and postcranial bones for identification. In some cases, we also collected bone fragments that contained identifiable anatomical remains (for example, a femoral or humeral head). We weighed and measured the length of each bone and identified each to the lowest taxonomic level possible while remaining conservative in our identifications (Bover et al. 2014, Fauteux et al. 2014, Johnson 2016). We used paired and unpaired mandibles for mammals and paired and unpaired femurs for birds to estimate the minimum number of individuals (MNI) in each pellet (Lambert 1981). We also used paired and unpaired mandibles (mammals) and femurs (birds) to estimate the overall MNI consumed across taxa to quantify prey proportionality in the diet. We removed data collected in October 2021 for this analysis since only 1 pellet was collected during that month. Data analyses To estimate home range, we first fit a continuous time movement model (CTMM; Calabrese et al. 2016) to the movement data (including stationary and non-stationary locations) and used this to generate 95% and 50% autocorrelated kernel density estimates (AKDEs). We performed an unsupervised classification of one-meter resolution Planet Lab SkySat Urban Naturalist A. Martin et al. 2026 No. 87 5 Imagery from 16 April 2024 to generate a land cover raster and estimate land cover composition of the home range (more details in Uiterwaal et al. 2026). We also divided the movement data by month and estimated both monthly range size and mean speed using CTMM. We intersected monthly ranges with park boundaries to determine the proportion of each monthly range that fell within park boundaries. We also used tri-axial acceleration data to estimate daily overall dynamic body acceleration (ODBA), which we used as a proxy for energy expenditure (Halsey et al. 2019). For each month, we estimated the mean daily ODBA as well as the total monthly ODBA. We estimated the daily foraging rate as MNI consumed per month using mandible or femur counts divided by the number of pellets, assuming 1 pellet is produced per day (Graber 1962, Marti 1973). We calculated this both by prey taxonomic group as well as for all prey combined. We then estimated daily biomass intake (Field et al. 2013, Pagels and Blem 1984) using taxon-specific wet mass estimates for prey obtained from the literature or from direct measurements of individuals from Forest Park collected for other research. We converted both foraging rates and biomass intake to monthly rates for comparison with movement data. Lastly, we used Pearson’s product moment correlation to test for association between paired monthly movement and foraging metrics. We also tested for correlations between monthly mean temperature and monthly movement or foraging metrics. We obtained temperature data for Saint Louis City using Weather Underground (Wunderground) historical weather data (Weather History & Data Archive | Weather Underground 2024). We completed all analyses using R (v4.5.2, R Core Team 2025). Results Based on physical and laboratory findings, the Great Horned Owl in this study was healthy at the time of capture. Blood sex determination confirmed the owl to be female, and she was aged as AHY (after hatch year, i.e., adult) given her pairing with another owl. The owl was subjectively categorized slightly above ideal weight (mass = 1.704kg, body score = 3.5). However, this weight was still within normal limits and may have been of physiological value for the time of year, as individuals would be in preparation for the colder temperatures and higher energetic demands of early winter (Randloph 1973). Most absolute WBC counts were within normal range, although the basophil count was lower than the reference ranges (Ammersbach et al. 2015a, b). Additionally, a high percentage of lymphocytes present may have been associated with an infectious, inflammatory or neoplastic condition that was subclinical at the time of handling (Jones 2015). We collected mite-like ectoparasites from the feathers, though we did not identify them to species. We also found a low number of Haemoproteus spp. parasites in the blood smear, which we did not identify to species. Both parasites are commonly found in asymptomatic, free-living raptors, although clinical disease may be associated with Haemoproteus spp. infections, especially during other stressors such as rehabilitation and captive care (Valkiunas 2004). For a complete summary of physical and laboratory findings, see Supplemental File 1, available online at https://eaglehill.us/urnaonline/ suppl-files/urna-249-Martin-s1.pdf. We identified 2,155 bones within the collected pellets and identified them to the lowest taxonomic level while remaining conservative. When estimating MNI (Fig. 2A), we found that prey items which could not be identified below the order Rodentia and Peromyscus spp. mice accounted for a large proportion of the diet (23.31% and 22.88%, respectively), followed by murids (18%), birds (Aves, 10.59%), Microtus spp. voles that could not be identified to species (9.75%), Microtus ochragaster Wagner (Prairie Vole [9.75%]), rats (Rattus Urban Naturalist A. Martin et al. 2026 No. 87 6 Figure 2. Proportions of the total diet composed of each prey item. Pellets used to examine diet were collected from the roost of the pair of Great Horned Owls, of which the female was tagged. Paired and unpaired mandibles were used to determine MNI for all mammalian specimens, while paired and unpaired femurs were used for avian specimens. Panel (A) shows the diet when specimens were identified to the lowest taxonomic level possible while remaining conservative. In Panel (B) Sciurus spp. contains both S. carolinensis and S. niger, Muridae contains Mus musculus, Peromyscus spp. and Rattus spp., and Microtus spp. contains M. pinetorum, M. ochragaster, and any Microtus spp. bones that were unidentifiable to species. Urban Naturalist A. Martin et al. 2026 No. 87 7 spp., 4.66%), Microtus pinetorum Le Conte (Pine Vole [2.97%]), Mus musculus L. (House Mouse [2.12%]), and Sylvilagus floridanus Allen (Eastern Cottontail Rabbit [1.69%]). Shrews (Soricidae), Sciurus niger L. (Fox Squirrel), Sciurus carolinensis Gmelin (Eastern Gray Squirrel), and Didelphis virginiana Kerr (Virginia Opossums) each accounted for 0.42% of the overall diet. When generalizing taxa in order to examine higher-order-level differences (Fig. 2B), we found that murids overall made up 41% of the diet, followed by specimens identified to the level of Rodentia (23.01%) and Microtus spp. voles (22.59%). Birds composed 10.46% of the overall diet and Eastern Cottontail Rabbits composed 1.67%, while shrews, squirrels (Sciurus spp.) and Virginia Opossums each made up 0.42% of the diet. Generalized taxa data were used to compute seasonal diet composition (Fig. 3). We found avian bones in pellets consistently throughout the year, with a notable increase in May and September. Voles, murids, and Eastern Cottontail Rabbits were also common prey items across seasons. Squirrels, shrews and Virginia Opossums appeared to be more supplementary prey items, with squirrels present in December, March and September, opossums in January, March, April and May, and shrews only present in January. The e-OBS GmbH telemetry tag was active for one year. A complete summary of fixes gathered from this tag can be found in Supplementary File 1. The 50% and 95% AKDE home ranges (Fig. 1) were 42.68 ha (95% CIs: 40.71–44.67 ha) and 95.04 ha (95% CIs: 90.77–99.54 ha), respectively. The 50% AKDE home range primarily consisted of the area immediately surrounding the roosting location, while the 95% AKDE home range indicated more areas used outside of the roost. Land cover in the 95% AKDE was barren (15%), developed (17%), forest (43%), herbaceous (19%), and water (6%; Fig. 4). Land cover in the 50% AKDE was barren (3%), developed (10%), forest (71%), herbaceous (1%), and water (15%; Fig. 4). Barren land cover consisted of soil- or sand-dominated land, such as golf courses or baseball fields. Figure 3. A comparison of the proportion of the diet composed of the MNI of each taxon per month. Pellets used to examine diet were collected from the roost of the pair of Great Horned Owls, of which the female was tagged. Paired and unpaired mandibles were used to determine MNI for all mammalian specimens, while paired and unpaired femurs were used for avian specimens. Note that in this figure, Sciurus spp. contains both S. carolinensis and S. niger, Muridae contains Mus musculus, Peromyscus spp. and Rattus spp., and Microtus spp. contains M. pinetorum, M. ochragaster, and any Microtus spp. bones that were unidentifiable to species. Numbers above bars indicate the number of pellets collected and analyzed per month. Urban Naturalist A. Martin et al. 2026 No. 87 8 There was a positive correlation between monthly mean temperature and monthly 95% AKDEs that approached significance (p = 0.073, Fig. 5A). There was also a significant positive correlation between monthly mean temperature and monthly 50% AKDEs (p = 0.024, Fig. 5B). Monthly 95% AKDEs showed a significant negative correlation with the proportion of the range within park boundaries (p = 0.012, Fig. 5C), indicating that monthly range expansion occurred outside of the park and into heavily urbanized areas. There was a positive correlation between mean monthly temperature and monthly mean speed that approached significance (p = 0.062, Fig. 5D), as well as a significant positive correlation between monthly mean speed and monthly biomass intake (p = 0.031, Fig. 5E). All other tested correlations were neither significant nor approaching significance, including those involving ODBA. Discussion The Great Horned Owl in this study was healthy based on physical and laboratory diagnostics, a finding that was supported by successful fledging of two chicks in 2025. The pair also made several nesting attempts near the roost during this study, though all were unsuccessful. This may have been due to a lack of available nesting sites as Great Horned Owls are secondary cavity nesters (Rusch 1982) and old, hollow trees are often removed in urban Figure 4. Land coverage in the 50% AKDE home range of the female Great Horned Owl (consisting primarily of her roosting location) and 95% AKDE home range (indicating her most used areas outside of her roost). Land cover in the 50% AKDE home range consisted mostly of forested land (71%) followed by water bodies (15%), developed areas (10%), barren land (consisting of dirt- or sand-dominated space, 3%) and herbaceous coverage (1%). Land cover in the 90% AKDE home range was forest (43%), herbaceous (19%), developed (17%), barren (15%), and water (6%). Urban Naturalist A. Martin et al. 2026 No. 87 9 parks for visitor safety. The assessment of a healthy, reproductively active Great Horned Owl was a positive finding given that urban raptors generally – and Great Horned Owls more specifically – have significant morbidity and mortality associated with anthropogenic impacts of urban areas (Deem et al. 1998, Franson and Little 1996). Murids were the most common prey species found in the pellets, with Peromyscus mice being the most abundant taxonomic group within this general categorization (Fig. 2). This finding coincided with those of other studies that found Peromyscus mice to be abundant in the diets of both rural (Bogiatto et al. 2003, Zimmerman et al. 1996) and urban (Hindmarch and Elliott 2015) Great Horned Owls. We also found proportions of avian specimens comparable to other urban parks (Hindmarch and Elliott 2015). This suggests increased consumption of avian prey in more urbanized environments, given that most rural studies – with the exception of Bogiatto et al. (2003) – report very few avian specimens (Lambert 1981, Marti and Kochert 1996, Zimmerman et al. 1996). Eastern Cottontail Rabbits and squirrels comprised a minor proportion of the diet, consistent with observations made by Hindmarch and Elliott (2015) in urbanized settings, yet in contrast to studies focused on Great Horned Owls in rural areas (Marti and Kochert 1996; Zimmerman et al. 1996). Notably, while Eastern Cottontail Rabbits account for less than 2% of the overall diet when estimated using MNI, their remnants were found in pellets from 7 out of the 11 months included in this analysis. These results suggest that Eastern Cottontail Rabbits were a common supplementary food source, likely due to the large caloric potential of these prey items compared to smaller taxa such as shrews or birds. Figure 5. Significant (A, B, C, E) and near significant (D) correlations between movement and foraging metrics of the Great Horned Owl, and temperature with lines of best fit and 95% confidence intervals. Urban Naturalist A. Martin et al. 2026 No. 87 10 Additionally, we found that voles constituted a smaller proportion of the overall diet here as compared to findings from rural landscapes in Oregon (Kopij 2016) and Idaho (Marti and Kochert 1996) and from both rural areas and urban parks in British Columbia (Hindmarch and Elliott 2015). The lower proportion of voles in the diet of these owls could be attributed to habitat differences between these studies, as many vole species prefer wetter habitats (Marti and Kochert 1996, Missouri Department of Conservation 2025). Two out of the three aforementioned studies describe a large body of water (either a lake or river) as a prominent feature of the landscape, whereas waterways only accounted for 6% of this owl’s overall range (95% AKDE), possibly explaining the smaller role of voles in this diet. Variation in the observed diet likely reflected the availability of prey in the home range (Kopij 2016, Zimmerman et al. 1996). During colder months (December through February) when many small mammals shift the timing of their activities to conserve energy (Guiden and Orrock 2020) and vegetation cover is lowest, the diet was more diverse, consistent with previous studies (Kopij 2016, Zimmerman et al. 1996). The increase of avian specimens in May and September supports this opportunistic foraging strategy based on prey availability, given increased songbird abundance during migratory periods (Robbins 2018). Several studies record high abundances of rats in the diets of urban Great Horned Owls (Hindmarch and Elliott 2015, Lambert 1981, Wink et al. 1987); however rats constituted less than 5% of the prey individuals found in the diet of this Great Horned Owl (Fig. 2). Rats are common targets of rodenticide applications within major cities, and rodenticide poisoning poses a serious concern to city predators, especially raptors (Hindmarch and Elliott 2015, Murray and Sánchez 2021). Additionally, rats are not the sole taxon susceptible to rodenticide poisoning, with biomagnification of these poisons occurring in mesopredators that can also become prey to urban raptors, such as Virginia Opossums (Buckley et al. 2024). Studies focusing on the dietary breadth and habitat use of urban raptors such as Great Horned Owls can help inform the growing understanding of urban trophic structure and potentially influence urban wildlife management decisions, especially when it comes to rodenticide applications. Home range estimates for Great Horned Owls vary widely, with few studies quantifying range size using telemetry. Bennet and Bloom (2005) report the mean core range (50% AKDE) size for 5 female Great Horned Owls living in a semi-urban environment as 27 ha and placed the mean boundary of home ranges (95% AKDE) at 180 ha. Other studies of Great Horned Owl home ranges in more rural areas report vastly larger estimates ranging from 300 ha to 600+ ha (Frank and Lutz 1997, Petersen 1979). Thus, our Great Horned Owl’s core and home ranges are more consistent with other reports on semi-urban owls. The core range consisted largely of forested land followed by developed land (Fig. 4). The roost lies on the east border of the park, adjacent to a major highway and hospital system, as well as a large visitor parking lot which contributes to the amount of developed land in the area. In her overall home range, this owl used more forested and herbaceous areas, although she continued to spend time in developed areas both inside and outside of the park. Much of her expansion outside of the core range was southward (Fig. 1). Given that the adjacent hospital system often produces substantial anthropogenic noise pollution, this southward expansion away from the hospital may have benefited foraging efforts. The inclusion of more forested and herbaceous areas in the broader home range also suggests preferences for hunting in these habitats since denser vegetation is likely to support higher Urban Naturalist A. Martin et al. 2026 No. 87 11 prey densities (Zimmerman et al. 1996). This may also be suggestive of the importance of forested patches within urban landscapes to provide urban raptors with foraging areas that are more secluded from anthropogenic noise pollution. We also found a significant correlation between overall range size (95% AKDE) and the proportion of the range that fell outside of park boundaries (Fig. 5). We found no such correlation with core range size (50% AKDE), highlighting high roost fidelity. Yet, as this owl increased her range she increasingly used more urban areas. We speculatively attribute this to territoriality between other nesting Great Horned Owls in the park (Baumgartner 1938, Bennet and Bloom 2005), although this claim requires further investigation. We found clear connections between temperature, movement, and diet. In colder months, the core range and overall range were smaller and mean speed was slower, indicating decreased movement activity. This aligns with energetic expectations, suggesting a behavioral trade-off that reduces energy expenditure for movement in favor of heat conservation in colder months. However, we note that reproductive behavior could also underlie the observed result, as both mating and nesting behavior can decrease movement. The breeding season of the Great Horned Owl is one of the earliest of the North American owls (Baumgartner 1938) and nest as early as January or February in Missouri (Missouri Department of Conservation 2025). As we had tagged the female of this pair, it is possible that this decrease in movement during these months could potentially be reflective of her nesting attempts; however, our limited scope does not allow us to attribute causation to these findings. Movement is critical to the predation process, with increased movement capacity often increasing encounter rates and success in prey capture. We did not detect a correlation between any of the tested movement metrics and the number of prey individuals consumed, as would be expected with increased encounter rates as movement increases. We did, however, identify a significant positive correlation between prey biomass intake and mean speed. This finding suggests that increased movement capacity better enables individuals to find and capture larger prey. Our data, however, do not allow us to directly examine causation between biomass intake and monthly speed. Predators are vital to the health and functioning of ecosystems (Glasser 1979). As urbanization continues to fragment native habitat, it also alters predator regimes (Rullman and Marzluff 2014) and increases human-wildlife conflicts (Soulsbury and White 2015). Our results showed consistent exploration of urban areas outside of park boundaries by this female Great Horned Owl, which increases chances of human-wildlife conflicts, morbidity, and mortality, especially when faced with high-traffic roadways. Trophic dynamics can also be greatly altered by human influence (El-Sabaawi 2018, Warren et al. 2006). Given that predators are expected to decline with increased urbanization (El-Sabaawi 2018), the continued presence of raptors in cities may make them one of the few remaining top predators in these areas (Donázar et al. 2016, Sergio et al. 2008). This case study highlights the complex interplay between environmental conditions, habitat use, and foraging behavior of an urban avian predator. Together, our findings contribute to our understanding of how urban raptors navigate ecological and humanimposed pressures, and they underscore the importance of considering both natural and anthropogenic factors when managing urban wildlife habitats. We emphasize, however, the limited scope of our project with a single individual. We hope to have provided a template for future research involving multiple individuals across urban gradients, as this research is necessary to determine relationships between movement ecology, foraging strategy, urbanization, and management of wildlife. Urban Naturalist A. Martin et al. 2026 No. 87 12 Acknowledgements Funding for this project was provided by the Saint Louis Zoo Institute for Conservation Medicine, Saint Louis University, the National Great Rivers Research and Education Center, and a Living Earth Collaborative seed grant from Washington University in Saint Louis. We thank Maris Brenn-White and Rimsha Malik for assisting with the capture of the owl. We also thank Johan Rhodin and Mark Glenshaw for their assistance in locating the roost, and Katy Huffman for her help in processing pellets. We also thank Amy Witt and Forest Park Forever. 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