Lasiurus frantzii

Western Red Bat

Family: Vespertilionidae · Class: Mammalia · Order: Chiroptera

Conservation status: G4 S3

The Western red bat is a medium-sized insectivorous bat with distinctive reddish fur coloration. Adults measure 105-125 mm (4.1-4.9 inches) in total length with a wingspan reaching 280-330 mm (11-13 inches). Males typically display brighter red pelage, while females exhibit more subdued reddish-brown coloration with frosted tips on the fur. The species possesses long, narrow wings adapted for swift flight and a furred interfemoral membrane that extends to the tip of the tail. Western red bats can be distinguished from Eastern red bats through genetic analysis, as the two species are morphologically similar and difficult to differentiate in the field. Historically, the Western red bat ranged throughout western North America from British Columbia to Central America. In California, the species occurs from sea level to approximately 2,400 meters (7,900 feet) elevation, inhabiting various regions including the Central Valley, coastal areas, and lower montane zones. Recent genetic confirmation has documented the species in Sutter County, demonstrating its continued presence in the Sacramento Valley region (CDFW 2024). Western red bats utilize diverse habitat types including riparian forests, oak woodlands, agricultural areas with trees, and urban environments with suitable roosting sites. The species shows strong preference for edge habitats where forested areas meet open spaces. Roosting typically occurs in foliage of deciduous trees, particularly willows, cottonwoods, and sycamores, where individuals hang from branches 2-4 meters above ground. Unlike many bat species that form colonies, Western red bats are largely solitary, with females occasionally roosting with their young. The species exhibits seasonal migration patterns, moving to warmer regions during winter months. Mating occurs during late summer and fall, with females storing sperm until spring fertilization. Gestation lasts approximately 90 days, with parturition occurring from May through July. Females typically produce 1-4 pups per year, with twins being most common. Young become volant at 4-6 weeks of age. Western red bats are aerial insectivores, foraging primarily on moths, beetles, and other flying insects captured during sustained flight patterns. Foraging typically begins shortly after sunset and continues throughout the night in areas 3-10 meters above ground or vegetation. The Western red bat holds a Global/State Rank of G4 S3, indicating the species is apparently secure globally but vulnerable in California. The California Department of Fish and Wildlife designates it as a Species of Special Concern. Primary threats include habitat loss due to riparian forest removal, urban development, and agricultural intensification. Pesticide use reduces insect prey availability and may cause direct mortality through bioaccumulation. Wind energy development poses collision risks during migration and foraging activities. Recently, the invasive fungus Pseudogymnoascus destructans, causative agent of white-nose syndrome, was confirmed in a Western red bat in California for the first time in 2024, representing an emerging conservation concern (USFWS 2024). Climate change may affect prey availability and suitable roosting habitat distribution. Conservation efforts focus on preserving riparian corridors, maintaining mature tree stands, and monitoring population trends across the species' California range.

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