Mammal Species of the World
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The distribution of the western mastiff bat is patchy. It can be found from the coast of the southwestern United States into central Mexico and southeast to Cuba. The northern limit of its range is the southern half of California. In the United States it extends southeast into western Texas through southern Nevada and southwestern Arizona. The southern limit of its range is in Argentina. This species is non-migratory (Hall, 1981, Allen, 1987, Cockrum, 1960).
Biogeographic Regions: nearctic (Native ); neotropical (Native )
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: (20,000-2,500,000 square km (about 8000-1,000,000 square miles)) Central California (Constantine 1998) southeastward to southern Nevada, central Arizona, and west Texas, and south through northern Baja California and central mainland Mexico (Muniz-Martinez et al. 2003), to Zacatecas and Hidalgo (Simmons, in Wilson and Reeder 2005); apparently a permanent resident in the United States. Also South America: northern Venezuela, western Ecuador, western Peru, Bolivia, northern Argentina, Paraguay, and eastern Brazil; Cuba (Simmons, in Wilson and Reeder 2005). Not known from Central America, but it may occur there (Best et al. 1996). Reaches elevations of about 1,100 meters in Texas and 3,000 meters in Peru
Eumops perotis is easily identified by large ears united across the top of its skull and projecting about 10 mm beyond its snout. It is the largest molossid in North America. Characteristic to the family Molossidae, its wings are distinctively long but rather narrow. Their flight membranes are tough and leathery. This is a free-tailed bat whith relatively large feet. Its pelage is short, velvety, and whitish at the roots. Coloration is dark to greyish brown dorsally and more pale ventrally. The dental formula is I 1/2, C 1/1, P 2/2, M 3/3 X 2 = 30. Both sexes of the western mastiff bat possess a peculiar dermal gland on the throat which looks like a pouch and produces an odoriferous secretion, athough this gland is much more developed in the males (Ahlborn, 2000; Texas Tech, 1997; Allen, 1987).
Average mass: 57 g.
Average length: 81 mm.
Range wingspan: 0.53 to 0.60 m.
Average wingspan: 0.56 m.
Other Physical Features: endothermic ; bilateral symmetry
Length: 19 cm
Weight: 65 grams
Size in North America
Average: 175 mm
Range: 159-187 mm
Range: 45.5-73 g
Differs from EUMOPS UNDERWOODI in a longer forearm (73-83 mm vs. 65-74 mm), longer ears (36-47 mm vs. 28-32 mm), broad square tragus rather than small and rounded, and greatest length of skull greater than 30 mm rather than usually under 30 mm (see Hoffmeister 1986 for further cranial distinctions). Much larger than other similar bats in western North America, where species with a free tail never exceed about 140 mm in total length or 64 mm in forearm length (EUMOPS GLAUCINUS of Florida, West Indies, and southern Mexico reaches 165 mm in total length and 69 mm in forearm length).
Habitat and Ecology
Suitable habitat for the western mastiff bat consists of extensive open areas with potential roost locations having vertical faces to drop off from and take flight, such as crevices in rock outcropings and cliff faces, tunnels and tall buildings. This species inhabits various types of open, semi-arid to arid habitats. These include coastal and desert scrublands, annual and perennial grasslands, conifer and deciduous woodlands, as well as palm oases (Ahlborn, 2000; Cockrum, 1960; Allen, 1987).
Range elevation: 5 to 300 m.
Habitat Regions: terrestrial
Terrestrial Biomes: desert or dune ; chaparral ; forest ; scrub forest
Other Habitat Features: urban ; suburban
Comments: North America: arid and semiarid, rocky canyon country habitats in the Chihuahuan Desert; roosts in crevices and shallow caves on the sides of cliffs and rock walls, and occasionally buildings. Roosts usually high above ground with unobstructed approach. Most roosts are not used throughout the year. May alternate between different day roosts.
Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: No. No populations of this species make annual migrations of over 200 km.
Apparently present year-round in Arizona (Hoffmeister 1986).
Western mastiff bats feed primarily on insects which they catch in flight. These bats rarely utilize night roosts and feed at night, with foraging ranges exceeding 24 km from roost sites, and a long foraging period of 6 to 7 hours. Prey includes relatively small, low-flying, and weak-flying insects. They usually feed from ground to tree-level but may soar to heights of some 60 m in rugged terrain. It is interesting to note that flightless insects, including ants and crickets, comprise part of their diet even though these bats are unable to take off from the ground, requiring that the prey be snatched up as the bat flies by. These prey items are likely to be taken from surfaces such as canyon walls (Cockrum 1960; Texas Tech, 1997; Ahlborn, 2000).
Some insect prey include: moths, crickets, grasshoppers, bees, dragonflies, leafbugs, beetles, true bugs, ants and wasps.
Animal Foods: insects
Primary Diet: carnivore (Insectivore )
Comments: Insectivorous. Feeds on various insects including moths, crickets (how these flightless insects are obtained is unknown), and longhorned grasshoppers. Appears to forage at considerable heights over extensive areas for long periods during the night (Barbour and Davis 1969).
Eumops perotis is an insectivore feeding primarily on flying insects.
Known prey organisms
This list may not be complete but is based on published studies.
Roosts in small colonies of generally less than 100 individuals. May fly more than 24 kilometers from roost sites while foraging (Vaughan 1959).
Life History and Behavior
Perception Channels: tactile ; chemical
Comments: In winter in North America, believed to exhibit daily diurnal torpor with nocturnal activity, rather than lengthy hibernation. Usually leaves daytime roost about one hour after sunset. In Arizona in midsummer, began leaving roosts to forage at around 8:00 p.m.; started to return at around 4:00 a.m. or slightly later (Hoffmeister 1986).
Males attract females with secretions from their enlarged dermal gland during the mating season.
Mating System: polygynous
Males and females of this species remain together throughout the year, including the period when young are produced. Mating occurs in early spring when the dermal gland of adult males is most functional and the testes enlarge and descend. Normally only one young is produced per pregnancy, with twins being very rare. Eumops perotis is a eutherian with a gestation period of approximately 80 to 90 days. The offspring are dull black in color at birth and are naked, except for tactile hairs on the feet and face. The period of parturition usually extends from June into July, varying more than for any other bat in the United States. A nursery colony of these bats may contain young ranging from newborn individuals to ones already several weeks old. Nursery roosts are located in tight rock crevices or holes in buildings at least 90 cm deep and 5 cm wide (Texas Tech, 1997; Ahlborn, 2000).
Breeding season: March to July
Range number of offspring: 1 to 2.
Average number of offspring: 1.
Range gestation period: 80 to 90 days.
Range weaning age: 1 to 2 months.
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous
Males remain with females during the period when young are produced but it is uncertain what degree of assistance in care they actually provide.
Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)
Breeds probably in early spring. Parturition dates vary extensively throughout range; in North America, young have been found as early as June and as late as August; probably most births occur in June and July. In Arizona, young a week old or younger have been found from mid-June through early August (Hoffmeister 1986). Litter size: usually 1. Adults males and females cohabitat in the same roosts throughout the year, even during period of parturition and lactation (unusual among bats) (Schmidly 1991).
IUCN Red List Assessment
Red List Category
Red List Criteria
- 2008Least Concern (LC)
- 1996Lower Risk/least concern (LR/lc)
Apparently, litte data is available for the current status of this bat species. Bat Conservation International lists Eumops perotis on its Threatened and Endangered Bats List due to the the fact that it uses only select drinking sites and is severely limited by the availability of drinking water. Because its wing structure is adapted for fast and straight-line flight, it is unable to drink from water sources less than 30 m long. As a consequence, western mastiff bats are no longer found in many previously occupied areas and populations may be in decline (Acker, 2001).
Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%. While there are currently no reports of Eumops perotis mortalities as a result of white-nose syndrome, the disease continues to expand its range in North America.
US Migratory Bird Act: no special status
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: least concern
- Cryan, P. 2010. "White-nose syndrome threatens the survival of hibernating bats in North America" (On-line). U.S. Geological Survey, Fort Collins Science Center. Accessed September 16, 2010 at http://www.fort.usgs.gov/WNS/.
- National Park Service, Wildlife Health Center, 2010. "White-nose syndrome" (On-line). National Park Service, Wildlife Health. Accessed September 16, 2010 at http://www.nature.nps.gov/biology/wildlifehealth/White_Nose_Syndrome.cfm.
National NatureServe Conservation Status
Rounded National Status Rank: N3 - Vulnerable
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Relevance to Humans and Ecosystems
This species sometimes roosts in high buildings or tunnels where it can be an unsightly nuisance.
Western mastiff bats feed on various insects and may play a role in controlling their populations, hence decreasing losses to agricultural products upon which these insects feed.
Positive Impacts: controls pest population
Western mastiff bat
- "Greater mastiff bat" redirects here. See Mops (bat) for the genus also known as "greater mastiff bats".
The western mastiff bat (Eumops perotis), also known as the western bonneted bat, the greater mastiff bat, or the greater bonneted bat, is a member of the free-tailed bat family, Molossidae. It is found in the Western United States, Mexico and South America, and is the largest bat native to North America. The subspecies Eumops perotis californicus is a species of concern as identified by the U.S. Fish and Wildlife Service. The range of this subspecies is principally southwest desert regions of the United States, along the border with Mexico; however, the range extends as far north on the Pacific coast to Alameda County, California.
The western mastiff bat has a body length of 5.5 to 7.5 in (14 to 19 cm) and a wingspan of over 22 in (56 cm). It has chocolate brown fur and thirty teeth. The body mass of this species can range from 60 to 70 g (2.1 to 2.5 oz).
The western mastiff bat needs at least 3 m (9.8 ft) of open space under its roosting spot for takeoff. Its echolocationary squeaks, which are inaudible to humans in most bats, can be heard from up to 300 m (980 ft) away. During the day they form colonies of less than 100. Unlike most North American bats, they do not undergo either migration or prolonged hibernation, but are periodically active all winter.
- Chiroptera Specialist Group 1996. Eumops perotis. 2008 IUCN Red List of Threatened Species. Downloaded on 26 October 2008
- Steven Moore, Endangered Species Survey for Water Treatment Plant Number Two of the Alameda County Water District, Earth Metrics Inc., published by the Alameda County Water District, Report number 10445.003, October, 1990
- Burt, William H. and Grossenheider, Richard P.; A field guide to Mammals; Huoghton Mifflin press, 1903: pg 45
- tpwd.state.tx.us; Accessed 2/28/07
- enature.com; Accessed 2/28/07
Names and Taxonomy
Comments: Eumops trumbulli of South America formerly was regarded as a subspecies of E. perotis (see Simmons, in Wilson and Reeder 2005). The large gap between the North American and South American ranges suggests that E. perotis as currently defined may encompass more than one species (Simmons, in Wilson and Reeder 2005).