Eumops bonariensis
dwarf bonneted bat

The range of the mastiff bat, or Eumops bonariensis, extends from Veracruz, Mexico, through Central America and into South America. In southern South America mastiff bats are found throughout Paraguay, sections of Uruguay, and as far south as the Buenos Aires province in Argentina. Mastiff bats have only been found in the lowlands throughout this range. (Redford and Eisenburg 1992, Reid 1997)

Eumops bonariensis individuals are found at low elevations in dry, deciduous tropical forests as well as thorn scrub. (Eisenburg 1989, Nowak 1999, Reid 1997)

Eumops bonariensis is the smallest of the eight species which comprise the genus Eumops. Mastiff bats have agouti hair coloring. The base of each hair is pale while the tips are frosted. Bristles are not located on the rump but some short hairs can be found on the calcar, which is the bone that gives structure to the membrane between the tail and the hind foot. The snout is broad and flat with a few slight wrinkles on the lips. Their large ears are rounded and, when laid forward, touch the tip of the nose. The fur is soft and somewhat long (5mm). The dorsal side is gray-brown or brown whereas the ventral side is gray-brown. Little else is known specifically about this species but many physical traits are common to all Eumops species. Each species in this genus have a thick head with a broad muzzle. The eyes of Eumops are small compared to species of bats from other genera. Eumops have legs which are short, strong, and muscular with broad feet and a well developed fibula. The wings of Eumops are long, flat, and narrow giving them a high-aspect ratio. The dental formula for the genus is I:1/2,C:1/1,P:2/2, and M:3/3. Measurements (in mm) specifically for E. bonariensis are: head-body length 49-68, tail 28-47, hind foot 6-11, ear 12-19, and forearm 39-48. (Anderson and Jones 1984, Emmons and Feer 1990, Eisenburg 1989, Kunz 1982, Nowak 1999, Redford and Eisenburg 1992, Reid 1997)

Information specifically about the reproduction of mastiff bats is not well known. However, members of the family Molossidae typically have 1 young and breed once each year. Breeding occurs before ovulation, which occurs in the late winter or early spring. Gestation lasts 70-90 days. The resulting offspring weigh 3-4g but typically do not exceed 22% of the adult weight. (Grzimek 1989, Nowak 1999)

Eumops bonariensis individuals prefer to roost in tree holes and in the iron roofs of man-made buildings. They are considered common house bats in Paraguay. Activity peaks within 2 hours of sunset and then again before dawn. Eumops typically fly as fast as 65 km/hr but may reach as fast as 95 km/hr in groups. These bats live in groups that usually consist of 10-20 bats at least 6 meters off the ground. The bats of this genus roost high enough to gain the speed for flight required by their long narrow wings as each bat drops out of the roost. (Anderson and Jones 1984, Emmons and Feer 1990, Nowak 1999, Redford and Eisenburg 1992, Reid 1997)

The diet of mastiff bats consists of larger, hard-shelled insects, particularly beetles, as well as moths. Eumops are specialized for rapid aerial pursuit of these insects. The long narrow wings and the ability to retract their tail membrane allow the bats in this genus to reduce drag and enhance speed. Eumops have rapid and relatively straight flight compared to that of other insectivorous bats. Laterally placed eyes and ears give Eumops a wide field of perception, which aids in capturing prey. All Eumops emit echolocation "chirps" which are audible to humans. This system allows Eumops to locate prey and then catch it in mid-flight. (Emmons and Feer 1990, Findley 1993, Macdonald 1993, Nowak 1999, Redford and Eisenburg 1992, Reid 1997)

Positive benefits to humans unknown.

Negative effects on humans unknown.

Status is unknown.

Although fairly common throughout its range, the biology of Eumops bonariensis is not well understood.