ASSESSING HOW FOREST STRUCTURE SHAPES PREDATOR-PREY INTERACTIONS BETWEEN SPOTTED OWLS AND WOODRATS IN SOUTHERN CALIFORNIA
|Zachary Wilkinson; University of Wisconsin - Madison; firstname.lastname@example.org; H. A. Kramer, G. Jones, C. Zulla, J. Barry, K. McGinn, S. Sawyer, R. Gutierrez, M. Z. Peery|
The spotted owl is an old-forest nesting species that has shaped forest management for several decades in western North America. However, it remains unclear as to which habitat conditions are most influential on predator-prey interactions between spotted owls and their primary prey, woodrats. In southern California, spotted owl populations have declined substantially since the late 1980s for reasons that remain undetermined. Accordingly, we tagged ten nesting male owls in the San Bernardino Mountains, California with high resolution GPS transmitters while placing video cameras focused on their nests to: (i) characterize forest structure at successful prey capture sites; (ii) understand how habitat conditions influence prey delivery rates; and (iii) determine the extent to which habitat-mediated variation in prey delivery rates affects spotted owl reproduction. We identified 330 prey deliveries to nests including 91 (27.5%) dusky-footed woodrats, 73 (22.1%) white-footed mice, and 28 (8.5%) valley pocket gophers. Of these deliveries, we ascertained locations for 123 prey captures. Here, we present the results of resource selection function analyses relating habitat conditions to successful prey captures and how delivery rates affect spotted owl fecundity, plus discuss the implications of our findings for the management of rapidly changing forests in southern California.
ASSESSING TOP-DOWN AND BOTTOM-UP EFFECTS ON INTERACTIONS BETWEEN DUSKY-FOOTED WOODRATS AND SPOTTED OWLS IN THE SIERRA NEVADA
|Corbin C Kuntze; University of Wisconsin - Madison; email@example.com; Jonathan N. Pauli, John J. Keane, Brian P. Dotters, Kevin N. Roberts, Sarah C. Sawyer, Ceeanna J. Zulla, M. Zachariah Peery|
Understanding the extent to which species are governed by top-down (predation) versus bottom-up (resource) limitations can benefit the management of both predator and prey. The dusky-footed woodrat (Neotoma fuscipes) is an important prey species for California spotted owls (Strix occidentalis occidentalis), yet the relative importance of bottom-up versus top-down controls for woodrat populations remains uncertain. Based on a sample of 109 radio-collared individuals, we found that predation on woodrats was uniformly low within spotted owl territories that featured a mosaic of forested seral stages. Nevertheless, video monitoring at 15 spotted owl nest sites revealed frequent deliveries of woodrats to dependent young. To reconcile this apparent dissonance and understand the proportion and number of woodrats consumed by pairs of spotted owls we used a combination of woodrat trapping data, occupancy models, and mark-recapture analyses. Our results suggest that the top-down effects of predation on woodrats are relatively weak but, in conjunction with other studies, woodrat abundance is likely a key driver of spotted owl populations. Collectively, our findings can inform forest management practices intended to promote woodrat populations and improve spotted owl conservation in Sierra Nevada forests.
INTEGRATING GPS TAG LOCATIONS AND NEST MONITORING VIDEO REVEALS NEW INSIGHTS INTO SPOTTED OWL FORAGING BEHAVIOR
|Ceeanna J Zulla; University of Wisconsin - Madison; firstname.lastname@example.org; H. Anu Kramer, Gavin M. Jones, John J. Keane, Kevin N. Roberts, Brian P. Dotters, Sarah C. Sawyer, Sheila A. Whitmore, William J. Berigan, Kevin G. Kelly, Amy K. Wray, M. Zachariah Peery|
Characterizing habitat conditions that promote successful foraging by predator species is important for their conservation. However, distinguishing sites of specific successful prey captures from general locations of individual animals is not possible using traditional telemetry methods. We integrated high spatial and temporal resolution GPS tagging with video nest monitoring to identify foraging movement patterns, predation events, prey species captured, and habitat characteristics of sites where California spotted owls (Strix occidentalis occidentalis) captured prey. We monitored 15 males and their nests to identify 127 prey capture locations, 91 (72%) of which were identified to a specific prey species using video monitoring. Owls tended to capture woodrats, Neotoma fuscipes, a primary prey species, in areas with more: (i) large-tree forest, (ii) young forest, (iii) medium trees/medium canopy forest, (iv) heterogeneity, and (v) hardwood-conifer edge – while avoiding areas with more medium trees/high canopy forest. Owls primarily captured flying squirrels, Glaucomys oregonensis, a second primary prey species, in areas with more large-tree forest. This information can be used to strengthen conservation planning by incorporating mechanistic knowledge about which habitats promote the acquisition of key prey while also integrating conservation plans with forest restoration activities intended to promote resilient landscapes.
THE ROLE OF FORESTS AS MICROCLIMATES FOR SPOTTED OWLS
|Kate McGinn; University of Wisconsin-Madison; email@example.com; M. Zachariah Peery, John J. Keane, Benjamin Zuckerberg, William Berigan, Ceeanna Zulla, Zach Wilkinson, Josh Barry|
While large scale, extreme temperature events associated with anthropogenic climatic change threaten global biodiversity, smaller areas of habitat within a landscape may retain suitable conditions where individuals can seek refuge. The spotted owl is a climate-sensitive, older-forest specialist that is less heat tolerant than other birds, with relatively low upper critical temperatures and limited ability to dissipate heat. We have yet to understand how access to cooler microclimates influences spotted owls during heat waves. In the summers of 2019-2021, we used GPS-tagging, doubly-labeled water injections, and demographic modeling to 1) examine how habitat and elevation interact to influence the temperatures spotted owls experience and 2) measure the effect of cumulative heat exposure on physiological rates. We found that elevation, topography, and canopy cover are significant predictors for microclimates. We also found that water turnover rates, which confer heat dissipating behaviors, increase with temperature, but overall energetic expenditure is only weakly impacted by temperature. Results suggests that the habitat spotted owls select during the day sufficiently buffers individuals from direct heat stress in current conditions, but extreme thermal events impact individual physiology. We will additionally report on the effect of habitat and temperature extremes on spotted owl occupancy. This study, thus, will identify particular areas and forest types that serve as temperature refugia for spotted owls as the climate continues to warm and help integrate the conservation of this species into forest planning activities.
CONFRONTING THE HABITAT FRAGMENTATION - HETEROGENEITY PARADOX: DOES ENHANCED PREY ACCESSIBILITY BUFFER FORAGING COSTS BY SPOTTED OWLS IN PATCHY LANDSCAPES?
|Ceeanna J Zulla; University of Wisconsin - Madison; firstname.lastname@example.org; H. Anu Kramer, Gavin M. Jones, John J. Keane, Kevin N. Roberts, Brian P. Dotters, Sarah C. Sawyer, Sheila A. Whitmore, William J. Berigan, R. J. Gutiérrez, M. Zachariah Peery|
Tension exists between two paradigms guiding species’ habitat and biodiversity conservation. One suggests that habitat fragmentation negatively affects individual species, while the other suggests that habitat heterogeneity can benefit individual species that rely on multiple habitat types. The California spotted owl (Strix occidentalis occidentalis) is an exemplar of the conundrum, where spotted owls benefit from larger patches of mature forests for both nesting and foraging purposes, but also benefit from younger forest and hardwood edges for foraging. Thus, we integrated high resolution GPS tagging, nest video monitoring, and remotely sensed habitat data to test three predictions regarding relative costs and benefits of heterogeneous landscapes. We predicted that owls with more heterogeneous habitat within their home ranges 1) travel farther distances, 2) deliver more prey to nests and 3) have higher reproductive rates. To test these predictions, we GPS-tagged 15 nesting male spotted owls and deployed cameras at their nests, allowing us to measure fine scale movements and prey delivery rates. We documented 358 prey deliveries, primarily of dusky-footed woodrats (41.5%) and Humboldt flying squirrels (40.2%). We examine the relationships between habitat heterogeneity and owl movement distances, prey delivery rates, and reproductive rates – and discuss their implications for Sierra Nevada forest management.
BREEDING CONSTRAINTS SHAPE TERRITORIALITY AND VOCALIZATION PATTERNS IN SPOTTED OWLS
|Dana S Reid; University of Wisconsin-Madison; email@example.com; Connor M. Wood, Sheila A. Whitmore, William J. Berigan, H. Anu Kramer, Nick Kryshak, John J. Keane, Sarah C. Sawyer, R. J. Gutierrez, Holger Klinck, M. Zachariah Peery|
Vocal territory defense involves trade-offs with other life history demands, influencing territory size and thus resource partitioning and population density within a species. Here, we investigated how life history constraints affect territoriality and territorial vocal behavior in the California spotted owl (Strix occidentalis occidentalis) in the Sierra Nevada, California, USA, using high-resolution acoustic/GPS tags. We discovered significant differences in spotted owl vocal behavior and territoriality based on breeding status, with breeding owls with fledged young producing fewer and quieter territorial calls, calling within a restricted area around their nest location, and defending significantly smaller territories—but utilizing larger areas—than non-breeding owls. These results suggest that breeding spotted owls reduce their investment in territorial behaviors and spend more time rearing and provisioning offspring. Our finding that territoriality was strongly linked to breeding status has important ecological implications, suggesting that population density and space-use is fluid across the landscape even for a site-faithful, highly territorial species such as the spotted owl. Further, our results have key implications for passive acoustic monitoring programs and highlight the importance of using multiple call types, both territorial and non-territorial, to detect species of interest which may face similar vocalization constraints.