Bat activity across the vertical gradient of an old-growth redwood forest
Graduation Date
2011
Document Type
Thesis
Program
Other
Program
Thesis (M.A.)--Humboldt State University, Biological Sciences, 2011
Committee Chair Name
Joseph M. Szewczak
Committee Chair Affiliation
HSU Faculty or Staff
Keywords
Redwood forests, Humboldt Redwoods State Park, Old-growth redwoods, Humboldt State University -- Theses -- Biology, Bats, Stratification, Vertical, Echolocation, Chiroptera, Acoustic survey
Abstract
Throughout their global distribution, bats vary in their use of microhabitats along the vertical strata of forests. Ground-based detection techniques typically cannot sample canopy strata in taller forests as it falls beyond detection and netting range. High-flying bats, those that exploit the canopy and above-canopy edge, may avoid capture or be under-represented in assessments using these methods. To improve our understanding of how bats use forests, I assessed bat activity and species stratification along the vertical gradient near Bull Creek in Humboldt Redwoods State Park, Humboldt County, northern California. Humboldt Redwoods State Park is the tallest forest in the world, containing 70 percent of known trees over 107 m. Two coast redwood, Sequoia sempervirens, trees were equipped with full spectrum automated bat detector units at treetop (108 m), middle crown (50 m), and ground level (5 m) from April 2008 to November 2009, excluding December and January. I sampled 1,365 detector nights and recorded 3,796 echolocation sequences containing one or more calls. I identified the presence of 12 species: Corynorhinus townsendii, Eptesicus fuscus, Lasionycteris noctivagans, Lasiurus blossevillii, L. cinereus, Myotis californicus, M. evotis, M. lucifugus, M. volans, M. thysanodes, M. yumanensis, and Tadarida brasiliensis. Two species, L. blossevillii, and T. brasiliensis, were undocumented in previously published surveys from redwood forests. I recorded the highest amount of activity at the treetop and least at the middle crown for both trees (65% and 43% at treetop, 7% and 23% at middle crown and 28% and 33% at ground level). I observed a greater number of species present at ground level compared to middle crown and treetop detectors at both trees. However, the data revealed a difference in the species composition of calls recorded at each level. Non-Myotis species composed 95% of the calls at the treetop, 87.5% at middle crown, and 21% at ground level. Calls from all Myotis species averaged 71% of all calls recorded from the ground level compared to less than 4% at both middle crown and treetop detectors. There was a marked decline, but not an absence of activity, during late fall through early spring. The combination of a temperate climate and observations of larger, migratory species during November, February, and March suggests the potential for resident populations or inland migrants overwintering in these forests. My findings illustrate the need to consider the full vertical habitat when designing bat habitat use studies, as species composition varies across the vertical gradient in forests.
Recommended Citation
Kennedy, Jean-Paul, "Bat activity across the vertical gradient of an old-growth redwood forest" (2011). Cal Poly Humboldt theses and projects. 2067.
https://digitalcommons.humboldt.edu/etd/2067
https://scholarworks.calstate.edu/concern/theses/x633f342f