Graduate Thesis Or Dissertation
 

Ringtail (Bassariscus astutus) Survival, Home Range Size, and Rest Site Use in Southwest Oregon

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  • The ringtail (Bassariscus astutus) is a small, nocturnal, meso-carnivore that occupies mid-elevation forests in the southwest portion of Oregon. Ringtail are fully protected within Oregon, but a species of conservation concern as they may be vulnerable to habitat loss and fragmentation. Limited data exists regarding ringtail ecology in forested ecosystems, and demographic rates, home range size, and habitat associations have not been formally investigated in Oregon. To address these data gaps, I monitored radio-collared ringtail to estimate monthly, seasonal, and annual survival rates relative to sex and age. I also collected locations from GPS radio-collared individuals to estimate home range size, territorial overlap, and movement distances. Finally, I relocated radio-collared ringtail within diurnal resting structures to investigate characteristics important to ringtail use of rest sites and I identified characteristics of used rest structures (i.e., space where ringtail rested). I estimated survival rates for 20 male and 6 female ringtail from 2020 – 2022 using a known-fate framework and Program MARK. I monitored 6 – 7 radio-collared ringtail per month (x ̅=6.63,SD=4.09,range 3-16) throughout the two-year study. Model-averaged monthly survival estimates did not vary relative to sex, age, or season, thus resulting estimates of annual survival ranged from 0.70 (SE = 0.155, 95% CI: 0.355 – 0.909) during the first year of the study to 0.73 (SE = 0.149, 95% CI: 0.382 – 0.924) the second year. I estimated home range size for the breeding season only, including locations obtained between February 1 and May 31 each year. I estimated 95% KDE seasonal home ranges and found that home range size was highly variable among individuals, ranging from 1.85 - 7.19 km2 (x ̅ = 3.52 km2, SD = 1.56, n = 16) for males, and 0.74 to 5.31 km2 ((x ) ̅= 3.03 km2, SD = 2.28, n = 2) for the two females I monitored. I observed similar rates of intrasexual overlap of adjacent male ringtail territories (utilization distribution overlap index; UDOI: male:male pairs: n = 6, x ̅ = 0.068, SD = 0.066) and the two adjacent intrasexual female:male pairs (n = 2, x ̅ = 0.072, SD = 0.063) . The estimated mean distance travelled per night during the breeding season (Feb – May) was 1,036 m for 16 males (95% CI: 864.56 – 1213.7) and 629.99 m (SD = 294.99) for a single female monitored 22 nights. I identified 56 unique resting structures, and 31 occasions of rest site reuse. I characterized rest site habitat at 3 scales: 1) the plot scale, defined as the area within a 30 m x 30 m plot, centered at the rest structure, 2) the rest structure scale, or the habitat element within which the rest structure is located (e.g., log, tree, snag), and 3) the microsite scale, or area within a rest structure that contained the ringtail (e.g., cavity, chamber, etc.). I characterized a ringtail rest site as the characteristics measured at all 3 of these nested scales. I also searched along a random azimuth for 60 - 300 m from the used rest site for a live tree, snag, log, rock pile, brush pile, or woodrat (Neotoma fuscipes) nest, that could possibly be used as a resting site for a ringtail. I compared these nearby, potentially unused, available rest sites to used rest sites resulting in an equal number of used and available sites. The average ringtail rest site was characterized by steep slope, southwest aspect, and occurred within a stand of conifers trees with a deciduous component. Conifer snags were the most common rest structure type used by ringtail, representing 34% of all located resting structures, although hardwoods were used in a greater proportion to their availability (Χ^2 = 4.855, df = 1, n = 89, p-value = 0.0276, Yates’ correction for continuity). In addition, the proportion of tree resting structures used by ringtail was greater than expected in both cool and warm seasons (Χ^2 = 5.834, df = 1, n = 56, p-value = 0.0157, Yate’s correction for continuity). The probability of rest site use was less for live tree structures relative to snag rest structures and no other vegetation variables were strongly supported. The DBH of used live conifer tree structures (117.56 ± 11.15 cm [ x ̅ dbh ± SD], n = 6; U’ = 22, p = 0.006) were larger than the diameter of available live conifer structures (94.38 ± 4.09 cm [ x ̅ dbh ± SD], n = 27), although the diameter and height of snags and all hardwood trees used as resting structures were similar to sampled available structures. Estimates of annual survival were much greater than previously documented and ringtail in my study area made large movements with very little territorial overlap, suggesting forested systems in Oregon may confer fitness benefits relative to other habitat types across the species range. Habitat type appears to be a strong predictor of home range size as seasonal home range estimates from this study are much larger than estimates from riparian forests, but closely resemble estimates of denning ranges in conifer forests in northern California. Ringtail used live conifer trees as resting structures that were larger than sampled available live tree structures, but used snags and hardwoods that were similar in size to available structures. For ringtail, fine-scale characteristics may be less important than the presence of a tree rest structure in a suitable state of decay. Conservation and management actions that promote recruitment of ringtail rest structures by retaining decaying live trees and snags, particularly hardwoods, may directly benefit ringtail by providing sufficient rest cover. This study represents the first to measure ringtail vital rates within Oregon and within forested landscapes, and the first to use GPS collar technology to investigate ringtail space use and movement. My results suggest forested ecosystems in Oregon may provide high quality habitat where ringtail occur. However, future research should focus on understanding ringtail avoidance and selection of landscape scale habitat types across the annual cycle, as well as the influence of specific management actions on ringtail demographics, movement behavior, and habitat use.
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