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.
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