Eumops bonariensis
Dwarf Bonneted Bat
Description:
The Peter’s Mastiff Bat (E. Bonariensis) belongs to the genus Eumops and is the smallest
of the eight species (Hunt et al. 2003). Upper body parts were found to be reddish to
blackish-brown often speckled with gray hairs. Underside of body colored dingy to a
similar gray as on upper portion of body (Sanborn 1932). Colors may vary with
geographical location in Paraguay, with northwestern Chaco E. bonariensis being paler
than E. bonariensis from eastern Chaco and Paraguay (Hunt et al. 2003).
Figure 1. Eumops bonariensis (Dwarf Bonneted Bat)
Phil Myers
(photographer, copyright_holder),
Museum of Zoology, University of Michigan,
http://animaldiversity.ummz.umich.edu
Ears are broad and connected by a thin skin and when projected forward they reach out
past the tip of the proboscis. Lips appear smooth and upper lip has many stiff, short hairs
which project downward. Proboscis is broad and upper incisors are hook-like (Sanborn
1932).
This genus is thought to be a related link or transitional genus between other
species of the family Molossidae. Comparable characteristics include the third
commissure and metacone, in Eumops these characters are either absent or very minute,
whereas in other genera (Tadarida, Chaerephan, and Platymops) these attributes are
apparent on the third upper molar. The tragus can also be considered an intermediary
trait which is either very small or broad and flat (Sanborn 1932).
Distribution:
In South America E. bonariensis arise around the Patagonian subreigion, eastern
Brazilian highlands and coast, the Amazon Basin, the northern coast islands, and the
Pacific coast f Colombia and Ecuador. Eumops bonariensis occurs in Panama to
Patagonia in South America with the exemption of all the west coast. In Panama they are
thought to have a very limited distribution which is constrained to the xeric coastal
lowlands along the drainage of the Rio Piedras and Rio Chirigugua in southeastern
Chiriqui (Dolan and Carter 1979). E. bonariensis appear around altitudes of 240 m in
Panama, sea level to 1,000 m in Colombia, and 80 m in Venezuela (Hunt et al. 2003).
Figure 4. Distribution of Eumops bonariensis in North and South
America, 1, E. b. beckeri; 2, E. b. bonariensis; 3, E. b. delticus; and
4, E. b. nanus
Map source (Hunt et al. 2003)
Ontogeny and Reproduction:
Research in Yucantan, Mexico has indicated that adult males had testes 3 – 5 mm
in average length during March and May, 4 mm in September and October (Birney
1974). In Argentina one male had abdominal testes and another had scrotal testes in midJuly. On average the male’s glans penis was 1.5 – 2.5 mm in length. The external
covering of the glans penis is free of epithelial spines. It is oval at the origin and expands
distally to form 3 prominent lobes. One is dorsal and the other two are lateral which
connect along ventral midline and produce a V-shaped furrow that terminates at the
urinary meatus (Birney 1974).
Two females were captured during November in Bolivia and when examined
were discovered to have single embryos. Also in Yucantan, Mexico two other females
were captured which had fetuses, one measuring 8 mm in crown-rump length and the
other measuring 16 mm in crown-rump length during the month of March (Mares et al.
1995).
Ecology and Behavior:
In Paraguay, E. bonariensis was found in many diverse areas. In all it was
captured in six of the country’s seven biomes (Willig et al. 2000). In the Paraguayan
Chaco, the Dwarf bonneted bat was commonly found around homes. They will often
roost in the roofs of the homes that are made of overlapping, split, palm logs. Research
has indicated that they will use the same roosting sites for a number of years and even
then they may not drift too far away. Research has also indicated that they will roost with
other species.
They also were found being active over small ponds during evening and early
morning hours. E. bonariensis is an insectivore. Its diet has been known to contain
Lepidoptera, Coleoptera, Hemiptera, Scarabaeidae, and other unidentified insects (Hunt
et al. 2003). They fly high and fast and have been captured in mist nets. While resting
and throughout activity E. bonariensis emanate high-pitched calls that are audible to
humans.
Literature Cited:
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December 02, 2004 at
http://animaldiversity.ummz.umich.edu/site/accounts/information/Eumops_bona
riensis.html.
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Reference written by Jeremy Mueller, Biol 378 (Mammalogy), University of Wisconsin –
Stevens Point: Edited by Christopher Luddington. Page last updated 02-17-05.