Current Distribution Rangewide

Occurs primarily in the western-most portion of the species' range in California, Oregon, Washington, Nevada, Idaho with more occurrences in Arizona, Colorado, New Mexico, Texas, and Wyoming [1;2; both from 3]. There are extensive zones of intergradation with the other subspecies, C. t. townsendii, throughout much of its range in California, Nevada, Idaho, Oregon and Washington [3;1 cited from 4;5] with C. t. townsendii also occurring in possibly southwestern Montana and northwestern Utah [3]. Patchy distribution strongly correlated with the availability of caves and cave‐like roosting habitat, degree of human disturbance at roosts, and population centers occur in areas dominated by exposed, cavity forming rock and/or historic mining districts [3;4;5;7].

Known Populations in San Diego County

Occurrences found in El Monte County Park, Hellhole Canyon Preserve, Spring Canyon, Marron Valley Mitigation Bank, Otay Mountain Wilderness Area, Dulzura Conduit, Barret Reservoir Open Space, Bureau of Land Management, Hollenbeck Canyon Wildlife Area, Rancho Jamul Ecological Reserve, San Diego National Wildlife Refuge, Cleveland National Forest, Anza Borrego Desert State Park, Santa Ysabel West Open Space Preserve, Cuyamaca Rancho State Park, Santa Ysabel nEast Open Space, East Otay Mesa, Mason Wildlife Refuge, Portrero Park, Ramona Grasslands Preserve, Del Dios Highlands Open Space Preserve, and San Felip Valley Wildlife Area

List Status

SSC; Currently in evaluation process for State listing of Threatened and/or Endangered

Habitat Affinities

Species is found from inland deserts to the cool, moist coastal redwood forests, in oak woodlands of the inner Coast Ranges and Sierra Nevada foothills, and lower to mid‐elevation mixed coniferous‐deciduous forests [3;4;6;7]. Has been reported in a wide variety of habitat types ranging from sea level to 3,300 meters. For roosts and hibernicula, prefers open surfaces of caves or cave‐like structures, such as subsurface hard rock mines, and large undisturbed spaces in buildings, bridges, and water diversion tunnels [6]. Though roost availability may be low in California Coastal regions, roost fidelity may be quite high [8]. Most commonly found in abandoned mines in San Diego County and appears to be located wherever there are historic mining districts, including within the MSCP area [7].

Taxonomy and Genetics

In the Microchiropteran bat family Vespertillionidae [3;6]. California has two subspecies of Corynorhinus townsendii (C. t. townsendii and C. t. pallescens), as defined in the last taxonomic revision of the species [1 cited from 4].

Seasonal Activity

A late flyer, emerging an average of 46 minutes after sunset [9]. A study suggested 2 peaks of activity during the night. Another study showed that during lactation, females returned to the nursery roost up to 3 times per night, but after lactation remained away from the roost all night [5].

Life History/Reproduction

Colonial species. Maternity colonies form between March and June (based on local climate and latitude). Colonies typically range from a few dozen to several hundred individuals, with colonies of over 1,000 documented [3;6]. Most mating generally takes place in migratory sites and hibernacula between September/October and February, but many females are inseminated before hibernation begins [6;10]. Sperm is stored until ovulation occurs in spring. Gestation lasts 56-100 days, depending on temperature, size of the hibernating cluster, and time in hibernation. A single litter of 1 is produced annually, occurring between May and July [3;6]. Young are weaned in 6 weeks and fly 2.5-3 weeks after birth. Growth rate depends on temperature. Maternity group begins to break up in August. Females mate in their first autumn, males in their first or second autumn. About half of young females return to their birth site after their first hibernation. Subsequent return rates are 70-80%. A longevity record of more than 21 years has been reported and annual survival has been estimated at about 50% for young, and about 80% for adults [6].

Diet and Foraging

Foraging associations include edge habitats along streams and adjacent to and within a variety of wooded habitats. Tend to follow densely vegetated gullies when dispersing from the main roost, and spend the majority of their foraging time within a forested habitat [6;11]. Likely a Lepidopteran specialist, feeding primarily on both small and medium‐sized moths [6;7;10]. Beetles and a variety of soft-bodied insects also are taken. Captures prey in flight using echolocation or by gleaning from foliage. Flight is slow and maneuverable. Capable of hovering. Forages with many other species [10].

Dispersal

Relatively sedentary species makes short movements to hibernation sites [10]. Has been documented making one-way commute distances of 5-13 km on foraging ventures [7;11;12].

Threats

Threatened by disturbance of roosts that results in displacement of the colony, reduced reproductive success, or death; deliberate vandalism that kills or injures bats; and introduction of pathogens, particularly the fungus that causes White Nose Syndrome. Also impacted by pesticides, chemicals for mineral processing, wind energy developments, artificial lighting, pest control activities, small population size, climate change [3;4;6], new and renewed mining operations, urban and suburban development, and predation by non‐native species (domestic cats and black rats) [3]. Primary cause for decline in western San Diego County is likely rapid urbanization [4].

Literature Sources