Sheila Whitmore - Academia.edu (original) (raw)

Papers by Sheila Whitmore

The Condor, May 25, 2023

Barred Owls (Strix varia) have recently expanded westward from eastern North America, contributin... more Barred Owls (Strix varia) have recently expanded westward from eastern North America, contributing to substantial declines in Northern Spotted Owls (Strix occidentalis caurina). Passive acoustic monitoring (PAM) represents a potentially powerful approach for tracking range expansions like the Barred Owl’s, but further methods development is needed to ensure that PAM-informed occupancy models meaningfully reflect population processes. Focusing on the leading edge of the Barred Owl range expansion in coastal California, we used a combination of PAM data, GPS-tagging, and active surveys to (1) estimate breeding home range size, (2) identify patterns of vocal activity that reflect resident occupancy, and (3) estimate resident occupancy rates. Mean breeding season home range size (452 ha) was reasonably consistent with the size of cells (400 ha) sampled with autonomous recording units (ARUs). Nevertheless, false-positive acoustic detections of Barred Owls frequently occurred within cells not containing an activity center such that site occupancy estimates derived using all detected vocalizations (0.61) were unlikely to be representative of resident occupancy. However, the proportion of survey nights with confirmed vocalizations (VN) and the number of ARUs within a sampling cell with confirmed vocalizations (VU) were indicative of Barred Owl residency. Moreover, the false positive error rate could be reduced for occupancy analyses by establishing thresholds of VN and VU to define detections, although doing so increased false negative error rates in some cases. Using different thresholds of VN and VU, we estimated resident occupancy to be 0.29–0.44, which indicates that Barred Owls have become established in the region but also that timely lethal removals could still help prevent the extirpation of Northern Spotted Owls. Our findings provide a scalable framework for monitoring Barred Owl populations throughout their expanded range and, more broadly, a basis for converting site occupancy to resident occupancy in PAM programs.

Animal Conservation, May 9, 2021

Climate change and a long legacy of fire suppression are leading to an increased prevalence of ‘m... more Climate change and a long legacy of fire suppression are leading to an increased prevalence of ‘mega‐disturbances’ such as drought and wildfire in terrestrial ecosystems. Evidence for the immediate effects of these novel disturbances on wildlife is accumulating, but little information exists on longer term impacts to species and ecosystems. We studied the occurrence dynamics of an iconic old‐forest species, the spotted owl (Strix occidentalis), on a long‐term study area in the Sierra Nevada, CA, USA from 1989 to 2020 to evaluate their multi‐scale population response following a 2014 megafire (the ‘King’ Fire) that affected a portion of our study area. We found that extensive severe fire within spotted owl sites resulted in both immediate site abandonment and prolonged lack of re‐colonization by owls six years post‐fire. Sites that experienced high pyrodiversity – a mosaic of burn severities – were more likely to persist after the fire, but this effect was only apparent at finer spatial scales. A potentially confounding factor, post‐fire salvage logging, did not explain variability in the probability of either owls persisting at sites or sites becoming re‐colonized; effects could be attributed only to severe fire extent and pyrodiversity. Our study demonstrates the prolonged effects of severe fire on the occupancy of this forest‐dependent species, suggesting that forest restoration that reduces megafires could benefit spotted owls. Our work emphasizes that long‐term monitoring can offer surprising learning opportunities and provide unparalleled value for understanding and addressing emerging environmental concerns.

The Condor, Nov 1, 2016

We assessed the occupancy dynamics of 275 California Spotted Owl (Strix occidentalis occidentalis... more We assessed the occupancy dynamics of 275 California Spotted Owl (Strix occidentalis occidentalis) territories in 4 study areas in the Sierra Nevada, California, USA, from 1993 to 2011. We used Landsat data to develop maps of canopy cover for each study area, which we then used to quantify annual territory-specific habitat covariates. We modeled the relationships between territory extinction and colonization using predictor variables of habitat, disturbance (logging, fire), climate, and elevation. We found that forests with medium (40-69%) and high (!70%) canopy cover were the most important predictors of territory occupancy in all study areas, and that both canopy cover categories were positively correlated with occupancy. We used analysis of deviance to estimate the amount of variation explained by the habitat covariates (primarily medium and high canopy cover) and found that these covariates explained from 35% to 67% of the variation in occupancy. Climatic covariates were not correlated with occupancy dynamics and explained little of the variation in occupancy. We also conducted a post hoc analysis in which we partitioned canopy cover into 10% classes, because our original partitioning into 3 classes may have lacked sufficient resolution to identify canopy cover levels where occupancy changed abruptly. In this post hoc analysis, occupancy declined sharply when territories contained more area with ,40% canopy cover, and the amount of 50-59% and 60-69% canopy cover had a more positive association with occupancy than did 40-49% canopy cover. Our results suggest that some fuels treatments intended to reduce fire risk and improve forest resilience could be located within Spotted Owl territories without adversely impacting territory occupancy if such treatments do not consistently reduce canopy cover below 50%. We suggest that future work quantify components of forest structure (e.g., large tree density, vertical complexity) known to be selected by owls and relate these characteristics to occupancy and fitness metrics.

Landscape Ecology, Aug 4, 2023

Research Square (Research Square), Mar 18, 2022

The concepts of habitat fragmentation and heterogeneity are central to the conservation of biodiv... more The concepts of habitat fragmentation and heterogeneity are central to the conservation of biodiversity; yet understanding when landscapes transition from heterogenous to fragmented can challenge conservation in practice. Complex and sometimes di cult-to-measure responses of species, and ultimately biological communities, to habitat heterogeneity and fragmentation may re ect the outcome of life-history trade-offs shaped by different landscape properties. Objectives Here, we tested the hypothesis that a mosaic of forest stands improved hunting and breeding success for California spotted owls (Strix occidentailis occidentalis). Methods We integrated high-temporal-resolution GPS tags, video monitoring of nests sites, long-term assessments of reproductive status, and high-resolution remotely-sensed vegetation data in a mixed-ownership landscape in the Sierra Nevada, California. Results Spotted owls made shorter nocturnal movements when medium forest was prevalent in their territory. However, spotted owls delivered prey at a higher rate to nests sites when they had more forest edge in their territory, which presumably provided greater access to large-bodied woodrat prey. Further, spotted owl reproductive output was relatively high in territories that contained a mix of mature and open forest. Conclusions Thus, the bene ts heterogenous forests provide to hunting success appear to outweigh costs associated with additional commuting to foraging sites and provide emergent tness bene ts to spotted owls. We suggest that the line between habitat heterogeneity and fragmentation can be a complex one that varies not only among, but within, species. Further, understanding the effects of heterogeneity and fragmentation on biological communities will require more empirical and mechanistic studies of individual species.

Journal of Avian Biology

Vocal territory defense can vary within a species due to many factors such as sex and breeding st... more Vocal territory defense can vary within a species due to many factors such as sex and breeding status, influencing territory size and thus population density across a landscape. Therefore, understanding what influences variation in territorial vocalizations can help to illuminate trade‐offs between territoriality and other life history demands, which benefits our general understanding of animal ecology as well as helps to inform emerging passive acoustic monitoring approaches. Here, we investigated how sex and breeding status affected territoriality and vocal behavior in the California spotted owl Strix occidentalis occidentalis in the Sierra Nevada, California, USA, using high‐resolution acoustic/GPS tags. We discovered that territorial vocal behavior was related to breeding status and to a lesser extent sex. Breeding owls with fledged young had a less diverse vocal repertoire, produced fewer and quieter territorial calls, and typically called only when close to their nest. Males w...

Ornithological Applications

Predators are among the most threatened animal groups globally, with prey declines contributing t... more Predators are among the most threatened animal groups globally, with prey declines contributing to their endangerment. However, assessments of the habitat conditions that influence the successful capture of different prey species are rare, especially for small, cryptic predators. Accordingly, most predator conservation plans are based on the relative importance of habitats inferred from coarse-scale studies that do not consider habitat features contributing to hunting success, which can vary among prey species. To address this limitation, we integrated high-resolution global positioning system tracking and nest video monitoring to characterize habitat features at prey capture locations during the nestling provisioning stage for the Spotted Owl (Strix occidentalis) a small, cryptic predator that has been at the center of a decades-long forest management conflict in western North America. When all prey species were considered collectively, males provisioning nests tended to capture pr...

Landscape Ecology, 2020

Context Climate and land-use change have led to disturbance regimes in many ecosystems without a ... more Context Climate and land-use change have led to disturbance regimes in many ecosystems without a historical analog, leading to uncertainty about how species adapted to past conditions will respond to novel post-disturbance landscapes. Objectives We examined habitat selection by spotted owls in a post-fire landscape. We tested whether selection or avoidance of severely burned areas could be explained by patch size or configuration, and whether variation in selection among individuals could be explained by differences in habitat availability.

The extent to which wildfire adversely affects spotted owls (Strix occidentalis) is a key conside... more The extent to which wildfire adversely affects spotted owls (Strix occidentalis) is a key consideration for ecosystem restoration efforts in seasonally dry forests of the western United States. Recently, Jones et al. (2016) demonstrated that the 2014 King Fire (a "megafire") adversely affected a population of individuallymarked California spotted owls (S. o. occidentalis) monitored as part of a long-term demographic study in the Sierra Nevada, California, USA because territory occupancy declined substantially at territories burned at high-severity and GPS-tagged spotted owls avoided large patches of high-severity fire. Hanson et al. (2018) attempted to reassess changes in territory occupancy of the Jones et al. (2016) study population and claimed that occupancy declined as a result of post-fire salvage logging not fire per se and suggested that the avoidance of GPS-marked owls from areas that burned at high-severity was due to post-fire logging rather than a response to high-severity fire. Here, we demonstrate that Hanson et al. (2018) used erroneous data, inadequate statistical analyses and faulty inferences to reach their conclusion that the King Fire did not affect spotted owls and, more broadly, that large, high-severity fires do not pose risks to spotted owls in western North American dry forest ecosystems. We also provide further evidence indicating that the King Fire exerted a clear and significant negative effect on our marked study population of spotted owls. Collectively, the additional evidence presented here and in Jones et al. (2016) suggests that large, high-severity fires can pose a threat to spotted owls and that restoration of natural low-to mixed-severity frequent fire regimes would likely benefit both old-forest species and dry forest ecosystems in this era of climate change. Meeting these dual objectives of species conservation and forest restoration will be complex but it is made more challenging by faulty science that does not acknowledge the full range of wildfire effects on spotted owls.

Wildlife Society Bulletin

Owls play important cultural, ecological, and indicator roles throughout the world. Yet owls' cry... more Owls play important cultural, ecological, and indicator roles throughout the world. Yet owls' cryptic behavior has led to uncertainties about their basic ecology, including foraging, communication, and functional roles within the community, and potentially hindered the implementation of effective conservation measures. Here we demonstrate the potential for next-generation GPS tags capable of recording high-precision, minute-by-minute locations paired with other technologies to resolve some of these uncertainties. We combined high-precision GPS tagging data with infrared (IR) video recorded by arboreally-mounted cameras at 5 spotted owl (Strix occidentalis) nest sites in the Sierra Nevada, USA to provide a uniquely detailed examination of owl foraging patterns. Our approach allowed us to identify the precise time and location of 54 predation events and prey identity. We also used high-precision GPS tags with on-board audio recorders to map the vocal activity of 8 individuals by matching the time of vocalizations in the audio data to GPS locations recorded at one-minute intervals. The combined spatial and acoustic data revealed that nonbreeding males had the most widespread territorial vocal activity (i.e., producing 4-note territorial calls), while females provisioning fledglings displayed extensive nonterritorial vocal activity (i.e., producing many contact calls). Thus, the GPS-tag technologies we employed can provide opportunities to better understand owl foraging, communication, territoriality, and population dynamics. The methods we describe are time-and resource-intensive but can be paired with techniques that are more applicable at landscape scales, such as stable isotope analyses, LiDAR-based habitat analyses, and passive acoustic monitoring to link local processes to broad-scale ecological patterns. Therefore, our approach could be applied to many species whose behavior inhibits direct observation.

Global Ecology and Conservation, 2022

Ornithological Applications, 2021

Pesticide use is pervasive and the exposure of non-target wildlife has been well documented over ... more Pesticide use is pervasive and the exposure of non-target wildlife has been well documented over the past half-century. Among pesticides, anticoagulant rodenticides (AR) have emerged as a particularly important threat in forests of the western United States, with exposure and mortality reported for several species of conservation concern. To further quantify this threat, we collected specimens of Barred Owls (Strix varia) and Barred Owl x Spotted Owl hybrids from the Klamath and Cascade Mountains and Sierra Nevada in California, USA to use as indicator species for environmental contamination with AR and to infer exposure of closely related and ecologically similar Northern and California Spotted Owls (S. occidentalis caurina, and S. o. occidentalis, respectively). We tested 115 Barred Owl and 12 Barred Owl x Spotted Owl hybrid livers for 8 AR compounds and found high rates of exposure (62%) across our study area, and greater than previous studies in the Pacific Northwest. In additio...