Western Screech-Owls Research Articles

Western screech-owl occupancy in the face of an invasive predator

Invasive predators can alter ecosystem function and be detrimental to native wildlife by direct predation and through exploitative and interference competition. Barred owls (Strix varia), a native species in eastern North America, have expanded their range to Pacific Northwest forests, threatening native owls and community dynamics. The western screech-owl (Megascops kennicottii) is a species of conservation concern, and the apparent population decline coincides with the arrival of barred owls. We collected data in 2021 under a broad scale passive acoustic monitoring program at 2482 stations in nine study areas to evaluate western screech-owl distribution and potential threats to population persistence in the Pacific Northwest. We fitted single-species occupancy models to estimate barred owl and western screech-owl landscape use and identify important features of habitat. We quantified effects of barred owls on western screech-owl occupancy and detection probability using co-occurrence models. Barred owls used approximately 0.79 (95 % confidence interval: 0.72, 0.85) of our sampling locations. Western screech-owl occupancy and weekly detection varied by study area from 0.24 (0.15, 0.34) to 0.92 (0.89, 0.95) and 0.12 (0.08, 0.16) to 0.71 (0.69, 0.74), respectively. Western screech-owl detection dropped slightly from 0.36 (0.31, 0.41) to 0.29 (0.26, 0.33) where barred owls were present. Western screech-owls frequently occupied sites used by barred owls but occurred less in older forests where barred owls were present, suggesting they may experience higher predation risk in older forests. Western screech-owls may be unable to avoid habitat used by ubiquitous barred owls, but they may adapt behaviorally to avoid this invasive predator.

Habitat-Patch Occupancy of Western Screech-Owls in Suburban Southern California

Many predators can adapt to human-altered habitats, but varying responses to human activity mean that the findings of studies of a species in one region may not apply even to related species at other locations. The Eastern Screech-Owl (Megascops asio) has been extensively studied in suburban environments, but comparatively little research has investigated to what extent the closely related Western Screech-Owl (M. kennicottii) persists in developed areas. I studied Western Screech-Owl occupancy in the town of Alpine in the foothills of San Diego County, California, finding the species at the majority of sites sampled, more likely in larger wooded patches and in those adjacent to undeveloped chaparral. The distance to and size of nearby wooded patches did not statistically influence occupancy. This study confirmed that the Western Screech-Owl can persist in suburban residential areas as does its eastern relative. Ensuring that patches of woodland remain larger than the minimum modeled threshold for the Western Screech-Owl’s occupancy, 4.2 ha, will be important for its persistence in the suburban sprawl of Alpine.

Comparing western (Megascops kennicottii) and whiskered (M. trichopsis) screech-owl microbiomes in southern Arizona using a novel 16S rRNA sequencing method

Microbiomes are essential to a host’s physiology and health. Despite the overall importance of microbiomes to animal health, they remain understudied in wildlife. Microbiomes function as physical barriers to invading pathogens, and changes in the diversity or composition of microbes within a host may disrupt this barrier. In order to use microbiomes in wildlife ecology, knowledge of the natural variation within and among species is essential. We compare the diversity and composition of two avian species that share the same habitat and niche in our study area, the western screech-owl (Megascops kennicottii) and the whiskered screech-owl (M. trichopsis). We used a targeted 16S sequencing method to improve the taxonomic resolution of microbiomes. We found similar measures of alpha diversity between species and sample types (cloacal samples vs. fecal samples). However, there were significant differences in bacterial species richness among nestlings from different nest boxes, and the composition differed between the two bird species and among nestlings from different nest boxes. Western screech-owls had more variation in alpha diversity and composition and had fewer bacterial species in their core microbiome than whiskered screech-owls. Siblings are likely to yield similar findings for microbiomes; thus, sampling nestlings from different nests may be most informative for monitoring population-level changes.

Differential landscape use by forest owls two years after a mixed‐severity wildfire

AbstractOwls are important avian predators in forested systems, but little is known about landscape use by most forest‐adapted owl species in environments impacted by mixed‐severity wildfire. To better understand species‐specific patterns of post‐wildfire landscape use within an owl guild, we used passive acoustic monitoring using autonomous recording units. The technology is effective for multi‐species surveys, especially if some species are rare, nocturnal, or difficult to detect by traditional means. In 2017, we surveyed the interior and adjacent unburned areas of a 10,700‐ha mixed‐severity wildfire that burned in 2015 in southwest Oregon. We used occupancy modeling to identify patterns of landscape use by five species of forest owls: barred owls (Strix varia), great horned owls (Bubo virginianus), western screech‐owls (Megascops kennicottii), northern pygmy‐owls (Glaucidium gnoma), and northern saw‐whet owls (Aegolius acadicus). Our results showed a positive relationship between increasing fire severity and probability of use by western screech‐owls and a similar but somewhat weaker relationship for northern pygmy‐owls. Barred owls were rarely detected in severely burned areas and their use decreased with increased fire severity. We observed generally low landscape use for great horned owls, which decreased with increased fire severity and at higher elevations. Thus, four out of the five species appeared to use recently burned forests at different levels, with only northern saw‐whet owls showing near‐complete avoidance of the burned area. These findings increase our understanding of the basic ecology of each species and highlight the varied use of burned areas within this community. These previously undocumented patterns of landscape use in burned landscapes should provide insights to managers and policymakers in the Pacific Northwest as climate shifts, and fires may increase in size, frequency, and severity.

Avian thermoregulation in the heat: metabolism, evaporative cooling and gular flutter in two small owls.

The thermoregulatory responses of owls to heat stress have been the subject of few studies. Although nocturnality buffers desert-dwelling owls from significant heat stress during activity, roost sites in tree and cactus cavities or in deep shade provide only limited refuge from high environmental temperatures during the day. We measured thermoregulatory responses to acute heat stress in two species of small owls, the elf owl (Micrathene whitneyi) and the western screech-owl (Megascops kennicottii), which occupy the Sonoran Desert of southwestern North America, an area of extreme heat and aridity. We exposed wild-caught birds to progressively increasing air temperatures (Ta) and measured resting metabolic rate (RMR), evaporative water loss (EWL), body temperature (Tb) and heat tolerance limits (HTL; the maximum Ta reached). Comparatively low RMR values were observed in both species, Tb approximated Ta at 40°C and mild hyperthermia occurred as Ta was increased toward the HTL. Elf owls and screech-owls reached HTLs of 48 and 52°C, respectively, and RMR increased to 1.5 and 1.9times thermoneutral values. Rates of EWL at the HTL allowed for the dissipation of 167-198% of metabolic heat production (MHP). Gular flutter was used as the primary means of evaporative heat dissipation and produced large increases in evaporative heat loss (44-100%), accompanied by only small increases (<5%) in RMR. These small, cavity-nesting owls have thermoregulatory capacities that are intermediate between those of the open-ground nesting nightjars and the passerines that occupy the same ecosystem.

Nest Habitat Selection of Western Screech-Owls (Megascops kennicottii macfarlanei) at Multiple Spatial Scales in Southeast British Columbia

The interior Western Screech-Owl (Megascops kennicottii macfarlanei) has been assessed as a species at risk. Regionally, survival rates are low, particularly during nesting. This study uses forward stepwise logistic regression to assess habitat selection at the tree, patch (150m2), and stand scales for twelve nests (the largest sample in any one region). At the patch scale, nest sites had more coniferous cover (33% versus 16%) than random. At the stand level, owls selected medium-age forests within an agricultural landscape, highlighting the need to conserve these habitats. While black cottonwood (Populus trichocarpa) and trembling aspen (P. tremuloides) are important nest tree species, riparian forests with coniferous cover, particularly western redcedar (Thuja plicata), may be more important for nesting in regional populations than previously realized.

Western Screech-Owls (Megascops kennicottii) Use Stump Nest During Active Logging Operation

Western Screech-Owls (<i>Megascops kennicottii</i>) Use Stump Nest During Active Logging Operation

Seasonal and Sex-Biased Survival of Adult Interior Western Screech-Owls (Megascops kennicottii macfarlanei) in Southeast British Columbia

In Canada and in British Columbia, the interior Western Screech-Owl (Megascops kennicottii macfarlanei) has been assessed as a species at risk primarily as a result of loss and degradation of low-elevation riparian habitat. Few data exist on population demographics of this subspecies. We analyzed annual survival of 19 radio-tagged adult owls from 2009 through 2013 using known-fate models. Time and sex dependence in annual survival rates were examined. The best approximating models suggested that female annual survival (28%) was lower than male survival (83%). Owl survival was lowest prior to incubation and during brood rearing, times when owls are most vocal. Mortality was attributed to avian predation and road mortality. Management practices to preserve habitat during the critical breeding period are encouraged in light of this research.

Raptor Presence Along an Urban–Wildland Gradient: Influences of Prey Abundance and Land Cover

Abstract Native animals are affected differently by urbanization. Some species respond favorably and thrive in human-dominated landscapes, but others are extirpated. Raptors are often sensitive to changes in land cover and prey abundance. We therefore used a combination of broadcast surveys and incidental observations while spot-mapping to evaluate the influences of these two variables on the presence of raptors at 21 sites from 2004–2008 along an urban-to-wildland gradient in western Washington, U.S.A. We detected three species of hawks: Sharp-shinned Hawk (Accipiter striatus), Cooper's Hawk (Accipiter cooperii), and Red-tailed Hawk (Buteo jamaicensis); and five species of owls: Northern Pygmy-Owl (Glaucidium gnoma), Western Screech-Owl (Megascops kennicottii), Barred Owl (Strix varia), Great Horned Owl (Bubo virginianus) and Barn Owl (Tyto alba). Models that included specific land-cover elements as independent variables explained presence for all species better than models including only prey abundance....

Residential edges as ecological traps

Substantial offspring mortality can occur during the postfledging period of birds, but few postfledging survival studies have been conducted within the context of habitat suitability. We conducted a 2-year radiotelemetry study of Spotted Towhee (Pipilo maculatus) reproductive success and fledgling survival in a 24-ha forested park in a residential area of Lake Oswego, Oregon. In corroboration of previous research on this species, we found (1) that Spotted Towhees nested closer to the edge between the park and residential neighborhoods than expected by chance, and (2) that pairs nesting near edges produced the largest and most offspring. However, fates were reversed during the postfledging period. Thirty-six of 52 fledglings survived the 27-day tracking period, and although fledglings were more likely to be found near edges than in the interior, fledglings near edges had a far higher probability of dying. All deaths were from predation, and at least 11 of 16 predation events were attributable to Domestic Cats (Felis catus) and Western Screech-Owls (Megascops kennicottii). A stochastic model that incorporated probability of nest success, nestling production from successful nests, and fledgling survival showed that the number of independent offspring produced per nest was greatest in the park interior. Heavy use of, and apparent preference for, edge by nesting Spotted Towhees, coupled with high fledgling mortality near edges, created a severe ecological trap that was not apparent until the final stage of parental care. Hence, failure to document offspring survival in the late stages of reproduction may lead to incorrect assessment of habitat suitability and poor management decisions.

First Record of Scavenging by a Western Screech-Owl (Megascops kennicottii)

Scavenging is a common behavior in many animal species and can increase the fitness of individuals and populations. Scavenging has been documented more commonly in recent years with advances in technology, including in difficult to observe avian species. Four North American owl species have been documented scavenging, and here we relate the first documented scavenging by a Western Screech-Owl (Megascops kennicottii), which was video-documented with a motion-triggered camera. The screech-owl visited a Virginia Opossum (Didelphus virginiana) carcass seven times over an 11-hr period, with the longest visit lasting 7 mins (mean = 3.14 ± SD 2.34 mins); during the visits the owl actively fed on the carcass. The most common prey of Western Screech-Owls are small mammals, insects, arthropods, and small birds. No mesocarnivore or large mammal has ever been detected in diet studies of screech-owls, though screech-owls have been shown to attack and kill prey larger than themselves. The importance of carrion in owl diets is largely unexplored, and the scavenging behavior of owls could be more significant than currently believed depending on its availability and the presence of competing scavengers. Further research is needed to establish the commonality of scavenging by owls, and its various ecological effects.

Recent Trends in Western Screech-Owl and Barred Owl Abundances on Bainbridge Island, Washington

In an ongoing 15-y study concerning population dynamics of Barred Owls (Strix varia) on Bainbridge Island, Kitsap County, Washington, I documented a steep decline in the Western Screech-Owl (Megascops kennicottii) population and a steady increase in the Barred Owl population. From 1995 through 2010, I conducted 358 auditory playback surveys that showed both changes in abundance and spatial distribution of both species on the island. Statewide Christmas Bird Count data from the same time period also reflect an overall decline in the Western Screech-Owl population and an increase in the Barred Owl population. Further, at least 2 other studies have shown Western Screech-Owl to be prey for Barred Owl, also contributing to the body of evidence that leads to a possible correlation between the increasing number of Barred Owls and the decline of Western Screech-Owls.

Home Ranges and Spatial Organization of Western Screech-Owls in Southern British Columbia

The macfarlanei subspecies of the Western Screech-owl (Megascops kennicottii) resides in the dry southern interior of British Columbia and is federally endangered in Canada. We captured and radio-tagged 11 adult screech-owls (6M, 5F) between July 2005 and January 2008 to collect ecological information needed to direct effective conservation. We collected point radiolocations from tagged owls to estimate seasonal and year-round home ranges with the 95% isopleth of the utilization distribution calculated using fixed kernel methods. Screech-owl home ranges averaged 64.5 ha (s = 10.6, n = 5), with no substantial difference in size between males and females. Owls used considerably smaller areas during the breeding season (x ¯ = 20.4 ha, s = 15.3, n = 7) than the non-breeding season (x ¯ = 88.6 ha, s = 44.5, n = 6). During the breeding season, males and females of a single pair overlapped extensively, whereas outside the breeding season very little overlap occurred within pairs. We did not detect overlap between neighbouring pairs. Home ranges of Western Screech-owls were highly associated with riparian forests; most screech-owls had ≥10 ha of riparian forested habitats within their home ranges. These results have implications for habitat conservation for this endangered species.

Factors Influencing the Detectability of Forest Owls in Southeastern Alaska

Patch-occupancy models offer a realistic approach to monitoring populations of nocturnal owls. However, because most owls are relatively rare, increasing the probability of detecting an owl at an occupied site will make estimates of occupancy more precise. We investigated the influence of temporal, biological, and environmental factors on rates of detection of forest owls in southeastern Alaska, 2005–2006. Following MacKenzie et al. (2006), we modeled probabilities of detection of the Northern Saw-whet Owl (Aegolius acadicus), Western Screech-Owl (Megascops kennicottii), and Barred Owl (Strix varia). We conducted 479 point counts over 100 days and detected owls 147 times. Sound broadcast increased detections 21–86% over silent surveys. During peak detection (9 April–8 May), probabilities (SE) of detection were 0.39 (0.13) for the Western Screech, 0.44 (0.16) for the Saw-whet, and 0.54 (0.25) for the Barred. For the Barred and Saw-whet, estimated occupancy probabilities (ψ) were constant (i.e., did not vary with covariates), but for the Western Screech, ψ was a function of whether large owls had been detected at a site, with estimated ψ about 66% lower at sites with large owls. For the Western Screech detection probability increased after sunset. For the Barred, the pattern of detection probability was nonlinear in relation to time after sunset, being high near sunset and late at night. For the Saw-whet detection probabilities were most influenced by weather covariates, primarily precipitation and wind. We provide recommendations on allocating survey effort and increasing probabilities of detection of these three owls in southeastern Alaska.

Entanglement of a Western Screech-Owl (Megascops kennicottii) in Coulter Spiderling (Boerhaavia coulteri)

Abstract We report an incident from southeastern Arizona of an adult western screech-owl (Megascops kennicottii) entangled in Coulter spiderling (Boerhaavia coulteri), a native forb. Boerhaavia thrives in open areas, such as heavily grazed rangeland and other anthropogenically disturbed land. Rapid urban development may create favorable conditions for proliferation of Boerhaavia and promote avian entanglements.

Mitochondrial DNA Variation and Phylogeography of the Eastern and Western Screech-Owls

AbstractAbstract. Sequences of the mitochondrial cytochrome b gene (930 base pairs) were used to examine patterns of variation within and between Eastern (Megascops asio) and Western (M. kennicottii) Screech-Owls, and to assess taxonomic affinity of Flammulated Owls (Otus flammeolus) and Whiskered Screech-Owls (M. trichopsis). Analyses support monophyly of the New World Megascops, a sister-group relationship between O. flammeolus and New World forms of Megascops, rather than with Old World Otus, and a closer relationship between the mostly North American M. trichopsis and South American Megascops than between M. trichopsis and North American Megascops. Megascops asio and M. kennicottii formed two distinct monophyletic clades, supporting species-level designations as suggested by morphology and song. Evidence for distinctive subspecies of eastern and western forms of screech-owls was less compelling. In the M. asio group, M. a. mccallii was the only subspecies with a unique haplotype; other subspecies within M. asio were phylogenetically indistinguishable. Subspecies within M. kennicottii were partitioned into three geographic groups, and differences are probably the result of barriers to gene flow (e.g., mountains above 2300 m), which are more pronounced throughout the distribution of M. kennicottii than in the distribution of M. asio.

MITOCHONDRIAL DNA VARIATION AND PHYLOGEOGRAPHY OF THE EASTERN AND WESTERN SCREECH-OWLS

Abstract Abstract. Sequences of the mitochondrial cytochrome b gene (930 base pairs) were used to examine patterns of variation within and between Eastern (Megascops asio) and Western (M. kennicottii) Screech-Owls, and to assess taxonomic affinity of Flammulated Owls (Otus flammeolus) and Whiskered Screech-Owls (M. trichopsis). Analyses support monophyly of the New World Megascops, a sister-group relationship between O. flammeolus and New World forms of Megascops, rather than with Old World Otus, and a closer relationship between the mostly North American M. trichopsis and South American Megascops than between M. trichopsis and North American Megascops. Megascops asio and M. kennicottii formed two distinct monophyletic clades, supporting species-level designations as suggested by morphology and song. Evidence for distinctive subspecies of eastern and western forms of screech-owls was less compelling. In the M. asio group, M. a. mccallii was the only subspecies with a unique haplotype; other subspecies wit...

Vocal individuality as a potential long-term monitoring tool for Western Screech-owls, Megascops kennicottii

Recent studies suggest that individually distinctive vocalizations found in many avian species can be used in population monitoring. In this study we assessed whether vocal identification of male Western Screech-owls ( Megascops kennicottii (Elliot, 1867)) was possible, and if it could be applied as a long-term monitoring tool. Recordings were collected between 2001 and 2003 from 28 territories on southern and central Vancouver Island. As a quantitative descriptor of the calls, a total of 17 variables were measured from each of 1125 calls. A discriminant function analysis resulted in 92.3% of calls being correctly classified to individual territories within one season and 87.3% of calls in a cross-validation of the model. Variables that showed the greatest discriminant ability included length of call, internote distance between first note and second note, and number of notes per call. Of the 14 territories that had owl calls recorded over 2 years, 4 appeared to be occupied by a different individual in the 2nd year, 7 had calls that were consistent between years, and 3 had calls that were ambiguously classified between years. Our results suggest that Western Screech-owl calls have enough individually recognizable characteristics to aid in the tracking of individuals both within and between years, allowing for long-term monitoring of individuals.

CHARACTERISTICS AND DISTRIBUTION OF ARDEA HERODIAS FANNINI WITH COMMENTS ON THE EFFECT OF WASHING ON THE HOLOTYPE

This owl gave a weak response to the call playbacks and quickly retreated into the cavity, behaviour which suggests it may have been incubating eggs at the time. The nest site was not visited again in 2003. This year, the nest site is active again and the pair has been heard calling at the same site on several nights throughout March and April 2004 (MAB). Acknowledgments. We thank S Clow, T Coopper and J Hobbs for reviewing the manuscript. We also thank L Ramsay for providing information on the western screech-owl in British Columbia.

The western screech-owl and habitat alteration in Baja California: a gradient from urban and rural landscapes to natural habitat

We studied the western screech-owl (Otus kennicottii) in the desert of the southern Baja California peninsula to determine its status and habitat selection and whether it benefits from moderate human-caused habitat changes. Based on the response to tape-recorded call broadcasts, western screech-owls were more abundant in undisturbed vegetation than in human-altered habitat. In man-made environments, more owls responded in rural than in urban areas; indeed, they were practically absent in urban areas. In natural areas, a total of 1.6 owls/km was estimated in the nonbreeding season and 2.7 owls/km in the breeding season. The most important habitat features selected in natural areas were greater shrub cover in the strata containing shrubs 1–2 and 2–3 m high and greater canopy cover of trees &gt;5 m high. In rural areas adjacent to cultivated areas, owls were present in areas with the greatest cover of shrubs 1–3 m high and a higher density of shrubs. The western screech-owl also occurs at lower densities in rural areas than in natural areas. Towns appear to be avoided in the arid desert of Baja California Sur. Western screech-owls may be still able to persist in rural areas that occupy an intermediate position on the gradient from a functional natural system (desert vegetation) to a completely altered ecological system, urbanized areas.