California Department of Fish and Wildlife

Bay Delta Region

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  Napa, CA 94558
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  Stockton, CA 95206
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Acting Regional Manager:
Scott Wilson

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Stanislaus River Report


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Stanislaus River Basin and Calaveras River Water Use Program
Threatened and Endangered Species Report - March 1995
Bay Delta and Special Water Projects Division, CA Dept of Fish and Game

Pallid Bat

Antrozous pallidus
California Department of Fish and Game "Species of Special Concern"
Two subspecies are recognized by E. Raymond Hall (1981) in California A.p. pacificus and A.p. pallidus.

Life History

Pallid bats have large eyes and separate ears. The coloration on the upper body is creamy to light brown and paler below. The tragus is long and lanceolate, longer than one half of the length of the pinna. The pallid bat has a pig-like muzzle and wart-like bumps on its face. The total length of the pallid bat measures 114 to 35 mm (Ingles 1965), the ear length is 23 to 37 mm, and the forearm length is 48 to 60.2 mm (Hall 1981). The females are generally heavier than the males.

Pallid bats occur throughout California, except in the high Sierra Nevada, from Shasta to Kern counties and the northwestern corner of the state from Del Norte and western Siskiyou counties (Hall 1981). These bats inhabit a variety of habitats, including grasslands, shrublands, woodlands, and forests from sea level up through mixed coniferous forests. They are common in grasslands and desert regions in the southwestern United States and most abundant in the sonoran life zones; less abundant in evergreen and mixed forests than in vegetation assemblages characteristic of lower elevations (Hermanson 1983). Pallid bats reside yearly in the majority of their range and they have been collected at sites up to 8,000 feet in elevation. In California pallid bats are associated with oak woodlands at lower elevations (BioSystems 1994) and may roost in a variety of places including tree cavities, rock crevices and man made structures.

Pallid bats travel 0.31 to 1.55 miles from the day roost for foraging. They will make longer movements to hibernation sites and for post-breeding dispersal, yet they are yearlong residents in most areas. Copulation occurs from late October to February and pregnancy averages nine weeks with one to three young born from April to July. Lactation may occur from the beginning of May through the middle of August; the young are weaned at seven weeks, and begin to fly at four to five weeks of age (Hermanson 1983). Pallid bats feed on large insects usually taken from the ground and activity is infrequent below 35 degrees Fahrenheit (2 degrees Celsius).

Findings and Conclusions

Pallid bats are very sensitive to disturbance of maternity colony sites. Because this bat is highly associated with oak woodlands and these woodland habitats are declining, so could the numbers of pallid bats.

Roosting and foraging habitat is found throughout the Stanislaus River, making this a likely species to be found. Any project which affects the oak woodland could negatively impact the pallid bats.