Distribution and ecology of the big-eared bat, Corynorhinus (=Plecotus) townsendii in Californa

Abstract

This study had two primary objectives: to conduct roost surveys C. townsendii in two parts of California where distributional information was most limited or lacking, and to obtain information on roosting and foraging ecology in two distinctly different habitats. This project was urgently needed because 1) recent California Department of Fish and Game surveys (conducted in 1987-1991) documented significant population declines in most surveyed areas, 2) distribution was still unknown in areas with suitable roosting habitat, and 30 the impact of various land management practices (e.g. prescribed fire, timber, harvest, agriculture, and grazing) on foraging behavior was unknown. A total of 95 abandoned mines, 18 caves, 11 man-made water tunnels, and 7 buildings were surveys for bats. Twenty-pne structures (twelve caves and nine mines) showed significant use by C. townsendii . Eleven are located in the western Sierra Nevada foothills, and ten in the Trinity Mountain area, Six maternity colonies, ranging in size from 48 to about 250 adult females, were identifies. Three were in caves, and three were in mines. Distribution for this species is somewhat patchy, and appears to be limited by the availability of roosting habitat. Historic and recent records would suggest that populations are concentrated in areas with abundant caves (especially the large lava flows in the northeastern portion of the state and karstic regions in the Sierra Nevada and Trinity Alps) or extensive abandoned mine working (particularly in the desert regions to the east and southeast of the Sierra Nevada). Radiotracking studies were conducted in two different habitats: 1) coastal forest (California bay, Douglas fir, and redwood) and grazed grassland at Pt. Reyes National Seashore, and 2) a mixture of scrub (with juniper and mountain mahogany) and ponderosa pine forest at Lava Beds National Monument. At Point Reyes they study colony resided in an abandoned ranch house, and at Lava Beds in a lava tube. In both settings the animals showed considerable loyalty to their roost sites even though the study was conducted after the nursery season had ended; females traveled greater distances than males to forage; and all the animals foraged in close association with vegetation -- in the vegetated gullies and redwood forest at Pt. Reyes, and in the vegetated lava trenches, near juniper or mountain mahogany, and with the stands of ponderosa pine at Lava Beds. Genetic variation was preliminarily examined for three populations using mitochondrial DNA and microsatellites -- two populations within the zone of intergradation between the two subspecies, C. t. townsendii and C. t. pallescens , and one population from the range of C. t. pallescens . These three populations were sufficiently distinct genetically to suggest that these techniques would be appropriated for addressing a wide range of questions for this species, including population differentiation, gene flow and mating systems. Most maternity populations appear to be declining in numbers, and many historic colonies no longer exist. The primary threat to this species appears to be human disturbance at roost sites, particularly recreational caving, renewed mining in old mining districts, and reclamation of abandoned mines for hazard abatement.