Corynorhinus townsendii

Townsend's Big-eared Bat

Family: Vespertilionidae · Class: Mammalia · Order: Chiroptera

Conservation status: G4 S2

Townsend's big-eared bat is a medium-sized vespertilionid bat distinguished by its exceptionally large ears, which measure 30 to 39 millimeters (1.2 to 1.5 inches) in length and extend well beyond the nose when laid forward. Adults have a forearm length of 39 to 48 millimeters (1.5 to 1.9 inches) and weigh 7 to 12 grams (0.25 to 0.42 ounces). The dorsal fur ranges from pale brown to dark brown, while the ventral surface is typically lighter buff to pale brown. The species exhibits distinctive facial features including prominent nose pads and when at rest, the large ears are coiled backward like ram's horns, giving the bat a distinctive appearance. The wing membranes are dark brown to black. Historically, Townsend's big-eared bat ranged throughout western North America from British Columbia to central Mexico. In California, the species occurs primarily in mountainous regions, coastal areas, and desert regions, with documented populations in the Sierra Nevada, Coast Ranges, Cascade Range, and Mojave Desert. The species has experienced significant range contractions and local extirpations, particularly in more developed areas of the state. Current distribution is fragmented compared to historical records. This species demonstrates strong fidelity to specific roosting sites and requires different roost types for different seasons. Summer maternity colonies typically form in warm locations such as attics, abandoned buildings, caves, and mine shafts, where temperatures remain stable for successful reproduction. Winter hibernation sites are usually in caves or mines with stable, cool temperatures between 0 to 11 degrees Celsius (32 to 52 degrees Fahrenheit) and high humidity. The species occurs from sea level to elevations exceeding 3,000 meters (9,800 feet) and utilizes diverse habitat types including coniferous forests, mixed woodlands, riparian areas, desert scrub, and agricultural lands adjacent to suitable roosting sites. Townsend's big-eared bat is an insectivore that employs passive listening and gleaning techniques to capture prey. The diet consists primarily of moths, particularly smaller species, but also includes beetles, flies, lacewings, and other soft-bodied insects. Foraging typically occurs in cluttered environments such as forest edges, riparian corridors, and around vegetation. Mating occurs in fall, with delayed fertilization until spring. Females form maternity colonies of 12 to 200 individuals from May through August, giving birth to a single pup after a gestation period of approximately 100 days. Pups are capable of flight at 3 to 4 weeks of age. The species holds a Global rank of G4 (apparently secure) but a State rank of S2 (imperiled) in California, indicating significant conservation concern at the state level. Primary threats include disturbance and destruction of roosting sites, particularly caves and abandoned structures, habitat fragmentation, pesticide use that reduces insect prey availability, and white-nose syndrome, though this fungal disease has had less impact on western bat species. Wind energy development poses an emerging threat in some regions. Conservation efforts focus on protecting known roosting sites, implementing seasonal restrictions on cave access, and maintaining suitable foraging habitat around roost sites.

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, and more.