Graduation Date

Fall 2018

Document Type

Thesis

Program

Master of Science degree with a major in Natural Resources, option Wildlife

Committee Chair Name

Dr. Daniel Barton

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Tim Bean

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Dr. Joe Szewczak

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Ted Weller, M.S.

Fourth Committee Member Affiliation

Community Member or Outside Professional

Subject Categories

Wildlife Management

Abstract

Winter roost (hibernacula) surveys offer a unique opportunity to monitor Townsend’s big-eared bats (Corynorhinus townsendii) while the population is generally closed, using a simple count method to census the population. Existing knowledge of C. townsendii hibernacula facilitates long-term population trend analysis but improving the accuracy of trend estimates requires identification of additional hibernacula to increase the proportion of the population monitored. Over 800 caves are known within Lava Beds National Monument; 322 of these have never been surveyed in the winter and could potentially hold a substantial portion of the C. townsendii population currently missing from the annual census. Given funding limitations, the process of selection for new survey sites should be carefully evaluated to improve the probability that new sites will contain larger numbers of bats, thus increasing the proportion of the population monitored. Therefore, I proposed and validated predictions for several habitat selection models built from multiple datasets for a species of concern, Townsend’s big-eared bats (Corynorhinus townsendii), threatened by disease (white-nose syndrome) and disturbance in an area with 30 years of survey history (Lava Beds National Monument, Siskiyou County, CA). Hibernating bat abundance in 30 caves was negatively correlated with mean winter cave temperature measured hourly over four years. However, the complexity of monitoring over 800 caves renders intensive temperature monitoring infeasible. Instead, I explored several cave morphology metrics thought to influence airflow as proxies for cave microclimate. Principal components analysis suggested a link between cave temperature and trench length, trench depth, and constriction area, but models built from an intensive dataset (n=30) did not perform well in predicting bat abundance. Boosted regression tree models built from an extensive dataset (n=191) were validated (n=50) and show moderate predictive performance using just three cave morphology variables. These most important predictors included interactions between number of entrances, passage slope, and passage size, along with cave length and trench length. Use of this model to prioritize unsurveyed sites could lead to faster discovery of important hibernacula, given the large number of caves to be surveyed and that most of them are unlikely to be occupied. Discovery of new hibernacula would increase the monitored proportion of the C. townsendii population that resides within Lava Beds National Monument, potentially providing a more accurate population monitoring program. As this C. townsendii population monitoring program provides the most consistent data at some of the largest known hibernacula in the western U.S., continued development and implementation of this program is critical to informing decisions related to this species of special concern.

Citation Style

APA

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