Bubo Virginianus Research Articles

Scale-dependent resource selection and space use by Mississippi Kite (Ictinia mississippiensis) in a heterogenous mixed-shrub ecosystem

Wildlife use and select habitat at multiple scales, sometimes leading to conflicting interpretations of the importance of various habitat features analyzed at different scales. Species can also exhibit affinities that are unique to portions within their larger distribution. Conservationists need spatially explicit information on habitat use to develop effective management strategies for priority species. This information can be difficult to obtain for species that are highly mobile or occupy large home ranges. In this study, we used a distance sampling approach to estimate multi-scale resource selection for a highly mobile raptor, Mississippi Kite (Ictinia mississippiensis), based on data collected from line transect surveys combined with plotting tools in a geographic information system. We compared land cover of kite detection points to randomly located points at fine and broad spatial scales in a portion of the species’ breeding range in the southern Great Plains, USA. Dominant cover in these landscapes is a mix of grasses, forbs, and expansive stands of a dwarf oak tree (Quercus havardii) generally < 1 m in height. Resource selection in Mississippi Kite was driven by both fine and broad-scale vegetation characteristics. At a fine scale (~ 13 ha), kites selected small, upland forest patches but avoided grass cover and riparian forest. At a broader scale (~ 200 ha), kites avoided oil pads but selected grass cover. Broad-scale selection also favored uplands farther away from riparian forest cover. Both observed density and predicted occurrence suggested riparian avoidance. Avoidance of riparian forest is atypical for Mississippi Kite, but might be explained in this system as avoidance of areas occupied by nest predators of kites, especially Great Horned Owl (Bubo virginianus).

Utility of Automated Species Recognition For Acoustic Monitoring of Owls

Presence or abundance of owls is frequently assessed using call-broadcast surveys to elicit responses and increase detection rates, but can draw owls in from a distance and could affect conclusions about fine-scale habitat associations. Passive acoustic surveys with field personnel or autonomous recording units (ARUs) may be a less biased method for surveying owls. Automated recognition techniques have proven useful to process large volumes of acoustic recordings from ARUs, and we sought to test the utility of automated recognition for three owl species. We built templates or “recognizers” for the territorial calls of the Barred Owl (Strix varia), the Boreal Owl (Aegolius funereus), and the Great Horned Owl (Bubo virginianus). We assessed the performance of each recognizer by evaluating precision, processing time, and false negatives. We used ARUs to survey for owls in northeastern Alberta, Canada, and compared the results from the recognizers to results from researchers listening to a subsample of the recordings. We verified the results to filter out false positives, but verification time was substantially lower than time spent listening. We processed more recordings and obtained a larger dataset of owl detections than would have been possible with either listening to the recordings only or conducting traditional field surveys without ARUs, suggesting a significant benefit of automated recognition. Precision was quite variable, but false negatives were relatively low and did not affect results of owl habitat associations. Given the relatively low detection rates of owls by listening to recordings, an automated recognition approach is likely to be highly useful for monitoring owls.

Extraocular muscle architecture in hawks and owls.

A complete and accurate understanding of extraocular muscle function is important to the veterinary care of the avian eye. This is especially true for birds of prey, which rely heavily on vision for survival and yet are prone to ocular injury and disease. To better understand the function of extraocular muscles in birds of prey, we studied extraocular muscle architecture grossly and histologically. This sample was composed of two each of the following species: red-tailed hawk (Buteo jamaicensis), Harris's hawk (Parabuteo unicinctus), great horned owl (Bubo virginianus), and barn owl (Tyto alba). All extraocular muscles were dissected and weighed. To analyze muscle fiber architecture, the superior oblique and quadratus muscles were dissected, weighed, and sectioned at 5μm thickness in the transverse plane. We calculated the physiologic cross-sectional area and the ratio of muscle mass to predicted effective maximum tetanic tension. Hawk and owl extraocular muscles exhibit significant physiological differences that play roles in ocular movements and closure of the nictitating membrane. Owls, which do not exhibit extraocular movement, have muscle architecture suited to stabilize the position of a massive, tubular eye that protrudes significantly from the orbit. Hawks, which have a more globose eye that is largely contained within the orbit, do not require as much muscular stability and instead have muscle architecture that facilitates rapid eye movement.

Superpredator proximity and landscape characteristics alters nest site selection and breeding success of a subordinate predator.

Selecting nesting habitat that minimizes predation risk but maximizes foraging success is one of the most important decisions in avian life history. This takes on added complexity when a predator is faced with the challenge of avoiding fellow predators. We assessed the importance of local and landscape vegetation, food abundance, and predation risk on nest site selection and nest survival in a subordinate raptor (Mississippi Kite; Ictinia mississippiensis) nesting in proximity to two superpredators, Red-tailed hawk (Buteo jamaicensis) and Great horned owl (Bubo virginianus). All three species nested in trees in a grassland landscape. In this landscape, kites favored upland trees and shrubs, avoiding their more typical riparian forest association elsewhere in the species' range. Compared to random conditions, kites selected nest sites with high tree density and more closed canopy in the surrounding area. Mississippi Kite selection was not related to food abundance but could be explained by the presence of superpredators (i.e., hawks and owls) selecting riparian woodland for their nests. Nest survival declined with proximity to superpredator nesting sites. Overall, our study demonstrates how landscape structure and superior predators shapes predation risk for subordinate predators. Our results emphasize the importance of spatial heterogeneity in presenting opportunities for subordinate predators to coexist in a landscape with important superpredators.

A RETROSPECTIVE SUMMARY OF RAPTOR MORTALITY IN ONTARIO, CANADA (1991-2014), INCLUDING THE EFFECTS OF WEST NILE VIRUS.

The causes of mortality of free-ranging raptors range from anthropogenic (e.g., trauma) to dynamic environmental conditions that may affect habitat suitability and prey availability. The province of Ontario, Canada, is vulnerable to anthropogenic and environmental changes because of its northern latitudes and expanding human populations, both of which may impact wildlife. We retrospectively evaluated diagnostic data from raptors submitted to the Ontario/Nunavut node of the Canadian Wildlife Health Cooperative (CWHC) from 1991 to 2014 ( n=1,448). Submissions encompassed 29 species, most commonly the Red-tailed Hawk ( Buteo jamaicensis; n=308) and Great Horned Owl ( Bubo virginianus; n=237). Trauma ( n=716) accounted for the majority of deaths among all species, followed by emaciation ( n=241). Traumatic deaths were most commonly attributed to collisions with stationary objects, and the odds of a diagnosis of trauma were significantly higher in adult versus immature raptors. The odds of being diagnosed with emaciation were significantly higher in males than in females but not in any age class or season. Mortality was less commonly attributed to infectious diseases ( n=214), for which West Nile virus (WNV) was the most common etiology, making up 53.1% of infectious diagnoses after its 2001 arrival in Ontario. The odds of a raptor being diagnosed with an infectious disease were significantly greater in summer and fall versus spring. Immature Red-tailed Hawks had significantly greater odds of being diagnosed with WNV compared to adults. These results reveal that human- and potentially environmentally-associated deaths (e.g., trauma and emaciation, respectively) are commonly diagnosed among Ontario raptors submitted to the CWHC. Infectious diseases are less commonly diagnosed, but WNV may have underlying, ongoing impacts on the health of some raptor species.

New data on Neodiplostomum americanum Chandler and Rausch, 1947 (Digenea: Diplostomidae), in the Great Horned Owl Bubo virginianus Gmelin, 1788 and the Eastern Screech Owl Megascops asio Linnaeus, 1758 in Mississippi, USA.

Neodiplostomum americanum Chandler and Rausch, 1947 has been reported from six species of owls in North America. At present, there are no molecular data for this species and gene sequence data from Neodiplostomum Railliet, 1919 are limited. A freshly deceased specimen of the Great Horned Owl Bubo virginianus Gmelin, 1788 and a freshly deceased specimen of the Eastern Screech Owl Megascops asio Linnaeus, 1758 were collected in Oktibbeha County, Mississippi in 2014 and 2016, respectively. Neodiplostomum americanum were recovered from both hosts. Herein, updated morphological descriptions are supplemented with gene sequence data from conserved (18S, ITS1-5.8S, ITS2, and 28S rRNA) and fast-evolving (cytochrome c oxidase subunit 1 mtDNA) regions. Preliminary phylogenetic analysis of the genus based on cytochrome c oxidase subunit 1 gene sequence data supports the placement of N. americanum within a discrete phylogroup of the family Diplostomidae. The life history of N. americanum is unknown and currently limited to the description of the adult stage in avian hosts. The molecular data generated in this study offer insight into the phylogenetic placement of N. americanum within the Diplostomatidae and will aid in identifying different life stages in putative intermediate hosts.

Variations in native protein glycation and plasma antioxidants in several birds of prey

Birds are an anomaly among vertebrates as they are remarkably long-lived despite having naturally high blood glucose and metabolic rates. For mammals, hyperglycemia leads to oxidative stress and protein glycation. In contrast, many studies have shown that domestic and wild birds are relatively resistant to these glucose-mediated pathologies. Surprisingly very little research has examined protein glycation in birds of prey, which by nature consume a diet high in protein and fat that promotes gluconeogenesis. The purpose of this study was to evaluate protein glycation and antioxidant concentrations in serum samples from several birds of prey (bald eagle (BAEA), red-tailed hawk (RTHA), barred owl (BAOW), great horned owl (GHOW)) as protein glycation can accelerate oxidative stress and vice versa. Serum glucose was measured using a commercially available assay, native albumin glycation was measured by mass spectrometry and various antioxidants (uric acid, vitamin E, retinol and several carotenoids) were measured by high performance liquid chromatography. Although glucose concentrations were not significantly different between species (p=0.340), albumin glycation was significantly higher (p=0.004) in BAEA (23.67±1.90%) and BAOW (24.28±1.43%) compared to RTHA (14.31±0.63%). Of the antioxidants examined, lutein was significantly higher in BAOW (p=0.008). BAEA had the highest beta-cryptoxanthin and beta-carotene concentrations (p<0.005). The high concentrations of antioxidants in these birds of prey relative to other birds likely helps protect from complications that may otherwise arise from having high glucose and protein glycation.

Complete genome sequence and evolution analysis of a columbid herpesvirus type 1 from feral pigeon in China.

Here, we report the genome sequence of a feral pigeon alphaherpesvirus (columbid herpesvirus type 1, CoHV-1), strain HLJ, and compare it with other avian alphaherpesviruses. The CoHV-1 strain HLJ genome is 204,237 bp in length and encodes approximately 130 putative protein-coding genes. Phylogenetically, CoHV-1 complete genome resides in a monophyletic group with the falconid herpesvirus type 1 (FaHV-1) genome, distant from other alphaherpesviruses. Interestingly, the evolutionary analysis of partial genes of CoHV-1 isolated from different organisms and areas (currently accessible on GenBank) indicates that the CoHV-1 HLJ strain isolated from pigeon (Columba livia) is closely related to the strains isolated from peregrine falcon (Falco peregrinus) in Poland and owl (Bubo virginianus) in USA. These results may suggest possible transmission of the virus between different organisms and different geographic areas.

Identification of a Novel Renal Coccidian (Apicomplexa: Eimeriidae) from the Great-Horned Owl ( Bubo virginianus ), USA.

We diagnosed renal coccidiosis in two of five Great-horned Owls ( Bubo virginianus ) examined in eastern Tennessee, US, 2007-13. Histopathologic examination of the kidneys revealed multifocal mild-to-moderate dilation and epithelial hyperplasia of collecting ducts. Renal collecting duct epithelial cells contained intracytoplasmic microgametocytes, macrogametocytes, and sporulating and sporulated oocysts. Renal coccidiosis in affected birds did not result in significant inflammation. Sequence analysis of the amplified partial 18S short subunit ribosomal RNA coding region from examination of formalin fixed tissue by using PCR disclosed a 93% identity to Eimeria reichenowi in GenBank, suggesting a novel Eimeria sp.

Survival and cause‐specific mortality of female eastern wild turkeys in two frequently‐burned longleaf pine savannas

Longleaf pine savannas have declined throughout the southeastern United States due to land‐use change. Fortunately, natural resource professionals are currently restoring these ecologically and economically important savannas. Although efforts are underway to restore longleaf pine savannas, little information exists on female eastern wild turkeyMeleagris gallopavo silvestrispopulation dynamics in these systems. Therefore, we evaluated survival and cause‐specific mortality of female eastern wild turkeys in two longleaf pine savannas in southwestern Georgia. We radio‐marked 126 female wild turkeys during 2010–2013 and monitored their survival; 66 (52.4%) radio‐marked females died during the study. We estimated causes of death for 37 mortality events with predation serving as the leading known cause of mortality, with 35.1% of mortalities attributed to mesocarnivore predation (e.g., bobcatLynx rufus, coyoteCanis latrans, and gray foxUrocyon cinereoargenteus) and 18.9% to great‐horned owlBubo virginianuspredation. One female (2.7%) was hit by a vehicle. Seasonal survival estimates varied from a high during fall (Ŝ = 0.94; 95% CI: 0.86–1.00) to a low during spring (Ŝ = 0.76; 95% CI: 0.68–0.87). Survival of incubating females was 0.82 (95% CI: 0.71–0.93) and survival of nonincubating females was 0.67 (95% CI: 0.52–0.87). Annual survival was 0.55 (95% CI: 0.44–0.67). To ensure sustainable wild turkey populations in longleaf pine savannas, we suggest managers monitor relationships between survival and population productivity.

Infecção por pox vírus e Aspergillus fumigatus em Bubo virginianus (Coruja jacurutu)

Resumo: Este trabalho descreve um caso de infecção mista por pox vírus e Aspergillus fumigatus em Bubo virginianus (coruja jacurutu). A ave, um macho adulto, foi encaminhada ao Núcleo de Reabilitação da Fauna Silvestre do Instituto de Biologia da Universidade Federal de Pelotas (NURFS/CETAS/UFPEL). Apresentava bom estado corporal, estava ativa, porém com incapacidade de voo. Após três dias apresentou lesões crostosas e de aspecto verrucoso na superfície dorsal das patas. Havia, também, nódulos de mesmo aspecto na pálpebra esquerda e na cera. A ave morreu após 15 dias de sua chegada ao NURFS e foi necropsiada no Laboratório Regional de Diagnóstico da Faculdade de Veterinária da Universidade Federal de Pelotas (LRD/UFPel). Histologicamente, as lesões verrucosas caracterizavam-se por hiperplasia do epitélio e nas células das camadas basal, espinhosa, granular e córnea havia corpúsculos de inclusão intracitoplasmáticos do tipo Bollinger. Na microscopia eletrônica foram visualizadas partículas virais características de pox vírus, incluindo Bubo virginianus como um hospedeiro do vírus. Havia, ainda, infiltrado inflamatório de células mononucleares e focos de colônias bacterianas na derme. Nos pulmões havia congestão e presença de granulomas com hifas fúngicas, que pela técnica de Grocott, apresentaram ramificação dicotômica compatível com Aspergillus spp., identificado na cultura como A. fumigatus. O diagnóstico de infecção por avipoxvirus pode contribuir para estudos relacionados com a ocorrência desta doença nas populações de vida livre e como informação auxiliar para o manejo e conservação desta espécie. Sugere-se, ainda, a inclusão do uso de raios-X nos protocolos de centros de reabilitação como o diagnostico de aspergilose em aves rapinantes com bom estado corporal, porém incapazes de voar.

Antibody Prevalence and Isolation of Viable Toxoplasma gondii from Raptors in the Southeastern USA.

Raptors are good indicators of the prevalence of Toxoplasma gondii in the environment because they prey on small mammals and birds. These prey species are a major source of infection in domestic cats ( Felis catus ), which shed the environmentally resistant oocysts. We assessed T. gondii infection in 281 opportunistically available raptors at a rehabilitation facility between 2012 and 2014. Antibodies to T. gondii were assayed by a modified agglutination test (cutoff 1:25) and found in serum of 22/71 Red-tailed Hawks ( Buteo jamaicensis ), 25/54 Barred Owls ( Strix varia ), 9/41 Red-shouldered Hawks ( Buteo lineatus ), 13/28 Great Horned Owls ( Bubo virginianus ), 6/20 Broad-winged Hawks ( Buteo platypterus ), 2/16 Eastern Screech Owls (Megascops asio), 12/13 Bald Eagles ( Haliaeetus leucocephalus ), 6/12 Cooper's Hawks ( Accipiter cooperii ), 1/8 Black Vultures ( Coragyps atratus ), and 1/1 Golden Eagle ( Aquila chrysaetos ). Antibodies were not detected in 5 Barn Owls ( Tyto alba ), 3 American Kestrels ( Falco sparverius ), 1 Mississippi Kite ( Ictinia mississippiensis ), and 1 Osprey ( Pandion haliaetus ). Viable T. gondii was isolated from the tissues of 1 antibody-positive Barred Owl and identified as a strain having type II alleles at all 10 loci tested, except one (ToxoDB polymerase chain reaction-restriction fragment length polymorphism genotype 3). Type II strain is the most common strain in the US. Results of this study indicate a high prevalence of T. gondii in some raptor species and the first reported genotyping from a Barred Owl.

Taphonomic comparison of bones in mountain lion scats, coyote scats, golden eagle pellets, and great-horned owl pellets

Bones consumed by carnivores and raptors, and subsequently deposited on the landscape in scats and pellets, respectively, can make up a considerable portion of the faunal remains recovered by North American archaeologists, particularly in caves and rockshelters. This paper compares and contrasts bones recovered from the scats of the mountain lion and coyote, as well as from the pellets of the great-horned owl and golden eagle. Bones in lion scats, coyote scats, and eagle pellets all may be relatively large in size, and display considerable etching, corrosion, and polishing, although bones in coyote scats tend to be smaller in size compared to those in lion scats. Bones in great-horned owl pellets tend to be larger in size and show much less degree of corrosion and polishing compared to the scats and eagle pellet bones.

Seasonal Effects of Habitat on Sources and Rates of Snowshoe Hare Predation in Alaskan Boreal Forests.

Survival and predation of snowshoe hares (Lepus americanus) has been widely studied, yet there has been little quantification of the changes in vulnerability of hares to specific predators that may result from seasonal changes in vegetation and cover. We investigated survival and causes of mortalities of snowshoe hares during the late increase, peak, and decline of a population in interior Alaska. From June 2008 to May 2012, we radio-tagged 288 adult and older juvenile hares in early successional and black spruce (Picea mariana) forests and, using known-fate methods in program MARK, evaluated 85 survival models that included variables for sex, age, and body condition of hares, as well as trapping site, month, season, year, snowfall, snow depth, and air temperature. We compared the models using Akaike’s information criterion with correction for small sample size. Model results indicated that month, capture site, and body condition were the most important variables in explaining survival rates. Survival was highest in July, and more generally during summer, when alternative prey was available to predators of hares. Low survival rates coincided with molting periods, breeding activity in the spring, and the introduction of juveniles to the sample population in the fall. We identified predation as the cause of mortality in 86% of hare deaths. When the source of predation could be determined, hares were killed more often by goshawks (Accipiter gentilis) than other predators in early successional forest (30%), and more often by lynx (Lynx canadensis) than other predators in black spruce forest (31%). Great horned owls (Bubo virginianus) and coyotes (Canis latrans) represented smaller proportions of hare predation, and non-predatory causes were a minor source (3%) of mortality. Because hares rely on vegetative cover for concealment from predators, we measured cover in predation sites and habitats that the hares occupied and concluded that habitat type had a greater influence on the sources of predation than the amount of cover in any given location within a habitat. Our observations illustrate the vulnerability of hares to predators in even the densest coniferous habitat available in the boreal forest, and indicate strong seasonal changes in the rates and sources of predation.

The Role of Bubo virginianus magellanicus as Rodent Bone Accumulator in Archaeological Sites: A Case Study for the Atuel River (Mendoza, Argentina)

AbstractMicromammalian bone assemblages from modern pellets of the strigiform Bubo virginianus magellanicus, from the upper Atuel River (southern Mendoza, Argentina), were taphonomically analysed. The results allow us to place B. v. magellanicus in the category of intermediate modification (Category 2). This sample has also been compared with results from other members of this genus, in order to classify B. v. magellanicus as a taphonomic agent. The participation of the Bubo species in archaeological accumulations has been documented, but in Argentina, the role of B. v. magellanicus has been reported up to the present. It is partly because of the sequence of one archaeological site in the south of Mendoza Province called Laguna El Sosneado‐3 (LS‐3). However, considering the absence of a current taphonomic model of this owl, this participation was mentioned as a hypothesis. In the current investigation, archaeological and modern samples have been compared. The results indicate that the skeletal element assemblages recovered from LS‐3 were accumulated by strigiform birds. Taphonomical evidence of light modifications on units I and IV indicates that Tyto alba (Category 1) was probably the main species involved in these units, whereas the taphonomical evidence on skeletal element assemblages recovered from units II and III suggests the action of a strigiform with a major category of modification such as B. v. magellanicus. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Molina’s Hog-nosed Skunk as prey of the Great Horned Owl: predation or opportunist scavenging?

This note reports the observation of an adult Great Horned Owl (Bubo virginianus) holding a Molina’s Hog-nosed Skunk (Conepatus chinga) in its claws. We assumed that it is a case of opportunistic predation because the skunk is larger than this owl’s regular preys. However, we could not exclude the possibility of opportunistic scavenging, despite this being an uncommon behavior for the Great Horned Owl. This is the first report of a Molina’s Hog-nosed Skunk preyed by a Great Horned Owl, an unusually large prey to an owl that preys mainly upon small mammals (e.g. rodents). Also, it is an uncommon report of consumption of mammal carnivores by owls in South America.

Eagles, owls, and coyotes (oh my!): Taphonomic analysis of rabbits and guinea pigs fed to captive raptors and coyotes

There is the potential for multiple accumulating agents of small mammals (<4.5kg body weight) at fossil sites, however, the lack of diverse predator and prey experimental and actualistic studies often makes it difficult to attribute the accumulator(s) of small mammals. I report the results of experimentally created assemblages of rabbits (Oryctolagus cuniculus) and guinea pigs (Cavia porcellus) fed to a bald eagle (Haliaeetus leucocephalus), great horned owl (Bubo virginianus), and coyote (Canis latrans). The analysis provides a taphonomic assessment of two small mammal taxa that differ in size and build and are broadly representative of small mammals recovered from archaeological sites. The ingested and non-ingested portions of the prey remains were analyzed for skeletal-, digested-, deleted-, and fractured-part representation, bone breakage, and bone surface modifications. The rabbit and guinea pig samples are compared and taphonomic differences between predators and prey taxa are observed. The predators produced variable and distinctive intra- and interspecific skeletal-, digested-, deleted-, and fractured part profiles. Bone surface modification frequency differences between the samples show a mixture of significant and non-significant intra- and interspecific comparisons. This study expands the range of small mammal experimental and actualistic studies to include prey of underrepresented size and build (guinea pigs) and characterizes the signatures of predator accumulations of small mammals. Often archaeological assemblages feature a mixture of accumulators, this analysis of raptor and mammalian carnivore predation on rabbits and guinea pigs will aid in the differentiation of predation between raptors, mammalian carnivores, and humans in the archaeological record.

PHARMACOKINETIC PROPERTIES OF A SINGLE ADMINISTRATION OF ORAL GABAPENTIN IN THE GREAT HORNED OWL (BUBO VIRGINIANUS).

Gabapentin (1-[aminomethyl] cyclohexane acetic acid) is a γ-aminobutyric acid analogue that has been shown to be efficacious for neuropathic pain control in humans. Plasma gabapentin concentrations >2 μg/ml are considered effective in treating epilepsy in humans and are suggested to provide analgesia for neuropathic pain. This study investigated the pharmacokinetics of a single oral dose of gabapentin suspension (11 mg/kg) in great horned owls ( Bubo virginianus ). Plasma gabapentin concentrations were determined in six healthy birds for 48 hr using high-performance liquid chromatography with mass spectrometric detection. Plasma gabapentin concentrations were estimated by noncompartmental pharmacokinetic analysis. The harmonic mean (±SD) maximum concentration (Cmax), time to maximum concentration (Tmax), and elimination half-life (tv2λZ) for gabapentin (11 mg/kg) were 6.17±0.83 μg/ml, 51.43±5.66 min, and 264.60±69.35 min, respectively. In this study, plasma gabapentin concentrations were maintained above 2 μg/ml for 528 min (8.8 hr), suggesting that gabapentin administered orally every 8 hr may be appropriate in great horned owls.

Landscape Differences around Nests of Great-Horned Owls and Red-Tailed Hawks

Nesting territories of great-horned owls (Bubo virginianus) and red-tailed hawks (Buteo jamaicensis) frequently overlap, with the owls using nests of other raptors. Records of use over a 22-year period in one locality were used to distinguish nesting sites used exclusively by great-horned owls, exclusively by red-tailed hawks, and those used by both. To determine the occurrence of various landscape characteristics within the proximity of a nest structure, I measured the total area of various land use types, total perimeter length, and the size of patches across six different land use types i.e., agriculture, pasture, residential, tree, pond, and roadside within circular plots around nests used by breeding pairs. The landscape features surrounding nests of great-horned owls differed from those surrounding red-tailed hawk nests in total perimeter length and size of patch. These differences are consistent with the fact that great-horned owls hunt from perches primarily at night using sensory modalities different than diurnal hunting red-tailed hawks.

Comparing the diet of Great Horned Owls (&lt;em&gt;Bubo virginianus&lt;/em&gt;) in rural and urban areas of southwestern British Columbia

We investigated the diet of Great Horned Owls (Bubo virginianus) in southwestern British Columbia. Our objective was to compare the diets of owls in urban and rural areas and determine whether urban owls consume a higher proportion of commensal rodents to understand possible pathways of secondary rodenticide poisoning of Great Horned Owls. Among 546 prey items identified at seven sites, Townsend’s Vole (Microtus townsendii [Bachman, 1839]) and rats (Rattus G. Fischer, 1803) were the two main prey items, making up 65.9% and 13.1% of the diet, respectively. The proportion of rats in the diet was positively correlated with the degree of urban development in the owls’ home range (rp = 0.83, P &lt; 0.05, df = 5).