Graduation Date

Fall 2019

Document Type

Thesis

Program

Master of Science degree with a major in Biology

Committee Chair Name

Joseph Szewczak

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Theodore Weller

Second Committee Member Affiliation

Community Member or Outside Professional

Third Committee Member Name

Matthew Johnson

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Barbara Clucas

Fourth Committee Member Affiliation

HSU Faculty or Staff

Fifth Committee Member Name

Paul Cryan

Fifth Committee Member Affiliation

Community Member or Outside Professional

Subject Categories

Wildlife

Abstract

The hoary bat, Lasiurus cinereus, is a solitary bat that roosts in the foliage of trees throughout the western hemisphere. Roosts are subject to the ambient temperature of their surroundings, thus hoary bats undergo long-distance migrations between summer and winter ranges to avoid freezing temperatures. Habitat selection has been studied during the summer for maternal female hoary bats, but not during migration and winter. Autumn migration coincides with the hoary bat mating period and it has been proposed that male and female bats may rendezvous on migration paths. Individuals may select roosts in stopover locations that enhance fitness by providing shelter, forage, or mating opportunities. Because of prior evidence that species of Lasiurusand other long-distance migrating bats forage infrequently at stopover locations, I hypothesized hoary bats select stopover habitat during autumn migration which minimizes energetic expenditures and improves mating opportunities. Specifically, I hypothesized that hoary bats would select areas with greater solar radiation and southwest aspects to exploit temperature at roosts in the autumn afternoons and that they might select roosts that serve as a landmark during migration i.e., emergent trees. I also hypothesized that they would roost in close proximity to flyways to increase mating opportunities (behavior demonstrated by previous studies).

I located 25 day roost sites of male hoary bats during the autumn in Humboldt Redwoods State Park through the use of radio telemetry (n=18) and GPS (n=7), then evaluated site-level roost selection by comparing roosts with 125 random sites within the study area. I used multiple logistic regression and Akaike’s Information Criterium to compare 64 multiple logistic regression models that assessed the possible influence of canopy height, distance to meadow, distance to road, elevation, emergent canopy, and solar radiation on hoary bat site use. Models were highly competitive and I used model averaging to generate parameter estimates. I averaged the top 14 models which cumulatively accounted for 95 percent of the total Akaike weight of all models. Elevation, distance to meadow, and distance to road had the highest variable importance ranking in the 14 models averaged. Elevation contributed to the 14 most highly-ranked models, distance to meadow contributed to 13 of 14 models, and distance to road contributed to 9 of 14 highly-ranked models. These three variables indicate that open space and flyways influence site use by hoary bats. Selection for open flyways is consistent with other roost studies on species of Lasiurus and seems to be the major driver of roost selection at the particular spatial scale at which my analysis was carried out. Further study on the drivers of roost selection is necessary at other spatial scales to more fully examine roost site selection by hoary bats during migration.

Citation Style

APA

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