Western Red Bat (Lasiurus frantzii)

Description: The western red bat (Lasiurus frantzii) is a medium-sized bat with short, broad, rounded ears that do not extend much above the dorsal fur. The nose is short and inornate. The posterior one-third of the interfemoral membrane is bare or only sparsely haired.

Color: Aptly named, the western red bat sports a pelage that ranges from rusty red to brownish. White- or silver-tipped hairs that gives the frosted appearance so characteristic of the closely related hoary bat may or may not be present; however, the face of a western red bat typically lacks these light-colored highlights.

Eastern Red Bat. Photo: By U.S. Fish and Wildlife Service Southeast Region

Eastern Red Bat. Photo: By U.S. Fish and Wildlife Service Southeast Region

Range: The western red bat occurs in the western United States from the western edge of the Great Plains to the Pacific Ocean (although it is mostly absent from the Great Basin); from northern California, southern Idaho, and southern Wyoming south to the U.S.-Mexico border including Arizona, New Mexico, and western Texas. South of the U.S.-Mexico border, the Western Red Bat occupies much of Mexico excluding the Mexican Plateau and coastal areas abutting the Gulf of Mexico and the Caribbean.

Recent studies have determined that in western Canada, old records formerly though to be those of the Western Red Bat have been confirmed genetically as the Eastern Red Bat. Current distribution records suggest a significant gap between the occurrence of Western Red Bats (e.g., there are currently no confirmed records of the species in Oregon or Washington) and the currently westward and southward expansion of the Eastern Red Bat from the north and east. The Eastern Red Bat is currently thought to be the only “Red Bat” occurring in western Canada.

Roosting: Western red bats are usually solitary, roosting in the foliage of large shrubs and trees, usually taking shelter on the underside of leaves. Often found hanging by one foot from the leaf petiole, they may occasionally hang from a twig or branch. However, they may also be found in rock crevices adjacent riparian corridors.

Roosting Red Bat. Photo: Chris Harshaw

Roosting Red Bat. Photo: Chris Harshaw

Characteristics: Western red bats roost along woodland borders, riparian corridors (especially with large sycamores) including oak riparian habitats, and urban areas with large (esp. large-leafed) trees. Other favored roosting trees include cottonwoods, sycamores, walnuts (and possibly other older, larges nut species), and older willows with dense leaf clusters.

Feeding: Western red bats are insectivorous. In most populations, moths comprised a large percentage of their insect prey. Foraging typically begins one to two hours after sunset. Foraging occurs in and amongst vegetation. Foraging habitats include oak woodlands, coniferous forest (at low elevations), along riparian corridors, among non-native trees in urban and rural residential areas, and within mature orchards. Western red bats may forage through most of the night within the initial foraging period commencing soon after sunset, a feeding hiatus spent at a temporary night roost followed by a secondary activity period prior to sunrise – often corresponding to a pre-dawn spike in insect activity.

Red bats may offer significant benefit to agriculture – this species can be found in habitats and agricultural areas adjacent to streams and rivers at some distance from known roosting habitats.

Migration: Some populations of the western red bat make north-south migrations in spring and fall. Other populations (e.g., along our Central Coast) may not and may simply hibernate for the short periods of time between suitable foraging periods. They may even interrupt extended period of hibernation for short periods during periods of warm winter weather.

Breeding: Mating occurs in late summer to early fall. Following delayed fertilization, the female will often give birth to pups in late spring to early summer (between early May and late June). There are typically two, occasionally three and up to five pups to a litter. Females remain solitary with their young at modest risk of predation to both mother and offspring – known predators include commonly occurring birds (e.g., western scrub jays) and arboreal mammals (e.g., raccoons, Virginia opossums).