General Distribution
Greater or western mastiff bats occur in two populations. One population is from the southwestern
United States to central Mexico and the second is located in the central and northern portions of South
America (Harvey and other 1999).
The western or California mastiff bat subspecies is primarily known from low to mid-elevations in
southern and central California southeast to Texas and south to central Mexico (Best and others 1996).
There are isolated records of the species occurring in northern California, and few records east of the
Sierra crest (Philpott 1997). Recent surveys in California (Brown report for West Mohave Plan Area)
have shown that western mastiff bats are "more widely distributed than was previously realized" and
significant populations occur in areas for which only single or scattered records were previously
available. Systematics
The genus Eumops contains eight species; three subspecies of E. perotis are recognized (Best and others
1996). Only E. perotis californicus occurs in North America. Habitat Requirements
Western mastiff bat is found in desert scrub, chaparral, mixed conifer forest, giant sequoia forests, and
montane meadows (Philpott 1997). In the southwestern United States, this species is most often
associated with upper and lower Sonoran life zones (Best and others 1996, Krutzsch 1943). In southern
California, most western mastiff bat roosts are found in semiarid areas with low-growing chaparral (Best
and others 1996) that do not significantly obstruct rock cliffs or outcrops.
Because of its large wingspan, the western mastiff bat requires roosts that have at least 6.5 feet (2
meters) of free space to drop from to initiate flight. In the southwestern United States, day roosts are
generally found in areas with rugged, rocky canyons and cliffs (Best and others 1996). Crevices in
granitic rocks and consolidated sandstone are a common roosting substrate (Best and others 1996).
These bats will also roost in building crevices—as nearly as many day roosts are known in buildings as
in natural crevices (Barbour and Davis 1969). They are found in cities such as Tucson and Los Angeles
(Best and others 1996).
It requires large bodies of flat water for drinking sites. Its long, narrow wings preclude it from drinking
at ponds less than 100 feet long (Bat Conservation International 2002). Reproduction
Copulation occurs in the early spring, and parturition occurs June–September (Barbour and Davis 1969,
Best and others 1996, Easterla 1972). Females typically give birth to one offspring. Females form
maternity colonies, although males may sometimes be present (Philpott 1997). Maternity colonies of 30
to several hundred (typically fewer than 100) individuals generally roost under exfoliating rock slabs (e.g.,
granite, sandstone, or columnar basalt) (Pierson 1998, Stephenson and Calcarone 1999). Daily/Seasonal Activity
Time of emergence from day roosts varies, but generally occurs from 40 minutes to 1.5 hours after
sunset (Barbour and Davis 1969, Best and others 1996, Easterla 1972). Western mastiff bats return
almost simultaneously and at a rapid rate to the day roost in the early morning (Best and others 1996,
Cox 1965). The foraging period is relatively long (approximately 6.5 hours), during which time the bat
flies continuously (Best and others 1996). Foraging may occur 6.2–15.5 miles (10–25 kilometers) from
roost sites (Vaughn 1959). Western mastiff bats have been observed to be active during foggy nights,
rainy nights, and violent thunderstorms (Vaughn 1959).
Western mastiff bats frequently vary their roosting sites; spending spring, summer, fall, and winter in
different roosts (Easterla 1972). They also alternate day roosts (Best and others 1996). The locations of
individual bats within the roost may also vary (Krutzsch 1955). These bats generally occupy the deeper
portions of crevices or open roosts in the morning, moving closer to the entrance in the afternoon (Best
and others 1996).
During the winter, this species becomes torpid on a circadian (24-hour) cycle (Leitner 1966).
Western mastiff bats appear to be periodically active all winter and likely seek winter refugia that are
protected from prolonged freezing temperatures (Texas Parks and Wildlife 2003). Diet and Foraging
Western mastiff bats are insectivorous and feed primarily on moths (Philpott 1997). They forage in
broad open areas including dry desert washes, flood plains, chaparral, oak woodland, open ponderosa
pine forest, grassland, montane meadows, and agricultural areas. They generally forage high above the
ground (Bat Conservation International 2002), and have been recorded to feed on insects carried by air
currents to altitudes higher than 1,000 feet (304.8 meters) (Best and others 1996, Vaughan 1959).
Western mastiff bats utilize large pools with open space for approach (Best and others 1996) and are
generally not netted over small ponds where other bats are frequently found (Best and others 1996).
They may forage 6–15 miles (10–25 km) away from roost sites (Vaughan 1959). Territoriality/Home Range
No information is available on territorial behavior. Individual bats may forage 6.2–15.5 miles (10 to 25
kilometers) from roost sites (Vaughn 1959). This species appears to move relatively short distances
seasonally (Texas Parks and Wildlife 2003). Predator-Prey Relations
Western mastiff bat is preyed upon by peregrine falcon (Falco peregrinus), American kestrel (F.
sparverius), red-tailed hawk (Buteo jamaicensis), and barn owl (Tyto alba) (Best and others 1996,
Easterla 1972, Sanchez and others 1993). White-throated swifts (Aeronautes saxatilis) have been
observed to harass this species (Easterla 1972). Literature Cited
Arizona Game and Fish Department. 1999. Arizona wildlife views (special edition). Phoenix,
AZ: Arizona Game and Fish Department.
Barbour, R.W.; Davis, W.H. 1969. Bats of America. Lexington, KT: The University Press of Kentucky.
Bat Conservation International. 2002. Bat Conservation International web site, species descriptions.
[Online].
Best, T.L.; Kiser, W.M.; Freeman, P.W. 1996. Eumops perotis. Mammalian Species No. 534. American
Society of Mammalogists; 1-8.
Brown, P. 2002. Species account for West Mohave Planning Area. Brown-Berry Biological Consulting,
134 Wilkes Crest, Bishop, California 93514.
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Cockrum, E.L. 1960. Distribution, habitat and habits of the mastiff bat, Eumops perotis, in North
America. Journal of the Arizona Academy of Science 1: 79-84.
Cox, T.J. 1965. Behavior of the mastiff bat. Journal of Mammalogy 466: 687-688.
Easterla, D.A.; Whitaker, J.O., Jr. 1972. Food habits of some bats from Big Bend National Park. Journal
of Mammalogy 53: 887–890.
Grinnell, J. 1933. Review of the recent mammal fauna of California. University of California
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Harvey, M.J.; Altenbach, J.S.; Best, T.L. 1999. Bats of the United States. Arkansas Game and Fish
Commission.
Howell, A.B. 1920. Contribution to the life-history of the California mastiff bat. Journal of Mammalogy
1: 111–117.
Johnson R.R.; Johnson, J.E. 1964. Notes on distribution of bats and other mammals in Arizona. Journal
of Mammalogy 45: 322–324.
Krutzsch, P.H. 1943. Zonal distribution of the California mastiff bat. Journal of Mammalogy 24: 269.
Krutzsch, P.H. 1945. Observations on a colony of molossids. Journal of Mammalogy 26: 196.
Krutzsch, P.H. 1955. Observations on the California mastiff bat. Journal of Mammalogy 36: 407–414.
Leitner, P. 1966. Body temperature, oxygen consumption, heart rate and shivering in the California
mastiff bat, Eumops perotis. Comparative Biochemistry and Physiology 19: 431–443.
Pierson, E.D. 1998. Western mastiff bat, Eumops perotis. In: Ecology, conservation, and management of
western bat species: bat species accounts. Unpublished document distributed at the Western Bat
Working Group Workshop, February 9-13, 1998, Reno, NV.
Philpott, W. 1997. Summaries of the life histories of California bat species. Unpublished document.
USDA Forest Service, Sierra National Forest, Pineridge Ranger Station.
Rowlett, R.A. 1972. First records of Eumops perotis and Microtus ochrogaster in New Mexico. Journal
of Mammalogy 53: 640.
Sanchez H.; de Lourdes Romero, C.M.; Vargas, A.R.; Gavino de la Torre, G. 1993. Noteworthy records
of some bats from Morelos, Mexico. Bat Research News 34: 1–2.
Stephenson, J.R.; Calcarone, G.M. 1999. Southern California mountains and foothills assessment:
Habitat and species conservation issues. General Technical Report GTR-PSW-175. Albany, CA: Pacific
Southwest Research Station, Forest Service, U.S. Department of Agriculture.
Texas Parks and Wildlife (Ed.). 2003. Texas Parks and Wildlife web site, species descriptions.
[Homepage of Texas PArks and Wildlife], [Online]. Available: http://www.tpwd.state.tx.us/.
Vaughan, T.A. 1959. Functional morphology of three bats: Eumops, Myotis, Macrotus. University
Kansas Publications, Museum of Natural History 12: 1–153.
Walton, D.W.; Kimborough, J.D. 1970. Eumops perotis from Black Gap Wildlife Refuge. Southwestern
Naturalist 15: 134–135.
Western Bat Working Group. 1998. Western bat species: Regional priority matrix. Developed at
Western Bat Working Group Workshop, Reno, Nevada, February 9–13, 1998.
Williams, D.F. 1986. Mammalian species of special concern in California. California Department of
Fish and Game, Wildlife Management Division Administrative Report (86-1): 1–112.
Information gathered from California DFG - California Interagency Wildlife Task Group
