Eumops perotis - Western Bonneted Bat​

Physical Description:

The western bonneted bat (Eumops perotis), also known as the Greater mastiff bat and the Western mastiff bat, is the largest bat in North America. Its wings are distinctively long but narrow, which does not allow much maneuverability around objects. It is a free-tailed bat that has large feet, and the pelage is short and velvety. The upper parts are brown to grayish brown with bases of the hairs being whitish, the under parts of the bat are paler. It has large ears that are connected across the forehead and protrude beyond the tip of the snout by 10 mm. Males have a peculiar glandular pouch on their throat which produces an odoriferous secretion, in females this gland is not as developed. The dental formula is I 1/2, C 1/1, P 2/2, M 3/3 . The external measurements average: total length 167 mm, tail length 57 mm, foot 17 mm, ear 40 mm, and forearm 76 mm (Chebes 2002).

Distribution:

Eumops perotis has a rather disjunctive distribution. Two subspecies are confined to South America (Venezuela, Ecuador, Peru, Bolivia, Paraguay, eastern Brazil, and northern Argentina) and also Cuba. The subspecies E. p. californicus ranges from the southwestern United States down through central Mexico. In the United States that range includes parts of California, southern Nevada, southern New Mexico, Arizona, and western Texas. The species is found in a variety of habitats which include desert scrub, chaparral, or oak woodland, however they prefer habitats where there are significant rock features offering suitable roosting sites (Best et al 1996).

Fig. 1 distribution of Eumops perotis http://www.funet.fi/pub/sci/bio/life/mammalia/chiroptera/molossidae/eumops/

Ontogeny and Reproduction:

Eumops perotis mates in early spring and the gestation period is approximately 80-90 days. Young are typically born in June or July and a nursery may contain young ranging from newborn individuals to ones that are already several weeks old. The parturition dates vary more for these bats then any other bat in the United States. Normally one young is produced per year, but occasionally a female may give birth to twins. Young are a dull black color at birth. Observation has indicated that males and females remain together throughout the year (Best et al 1996).

Ecology and Behavior:

Eumops perotis prefers rugged rocky canyons and cliffs where they can find roost sites in crevices, choosing long vertical slits at least 2 inches (50 mm) wide, from which they climb rapidly to a narrower spot and wedge themselves in. These crevices generally face downward so they can be entered from below. These bats can not take off from a flat surface on there own, so an unobstructed drop of several meters is required so that the emerging bats can gain sufficient momentum to become airborne. Colony size varies from two or three bats to several dozen, but generally never more than one hundred. These bats leave their day roosts late in the evening to forage. This species produces a high-pitched call that can be heard when they are flying up to 300 meters (990 feet) above ground. This call can often be heard in the evening when bats are getting ready to leave their day roost to feed (Cox 1965). Their diet consists mostly of moths (80%) but also eat ground-living crickets and long-horned grasshoppers. Since these bats can not take off from the ground these insects must be taken off canyon walls. These bats do not use night roosts but instead sore at high altitudes all night long in order to feed over wide areas. Insects that have been carried up by thermal currents are thought to make up a large part of their diet (Chebes 2002).

Remarks:

Since these bats make rather loud calls that can be easily heard, experts can use these calls to monitor the population size. In the southwest there has been a decline in calls which has showed a rather large decrease in the population size over the past 30 years (Chebes 2002).  The loss of large open water drinking areas seems to be a major threat to the species. Also destroying or disturbing key cliff habitat by building impoundments or quarry operations has caused a decrease in the population. Foraging may also be affected by pesticide application in agricultural areas (Best et al 1996). 

Literature Cited:

Best, T. L., W. Mark, and P. W. Freeman 1996. Eumops perotis Mammalian Species 534: 1-8.

Chebes, L. 2002. "Eumops perotis" (On-line), Animal Diversity Web.  Accessed October 27, 2004 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Eumops_perotis.html.

Cox, Thomas J. 1965. Behavior of the Mastiff bat. Journal of Mammalogy, 46(4): 687-688

Reference written by Tyler Haase, Biol 378 (Mammalogy), University of Wisconsin – Stevens Point:  Edited by Christopher Luddington. Page last updated 02-17-05.