Eptesicus diminutus
Diminutive serotine
Description
In South America, the genus Eptesicus is represented by seven species. There appears to
be size overlap between species, which has led to considerable confusion concerning the
applicable names for certain populations, and the identity of individual bats. Williams
(1978) studied three species of Eptesicus: E. diminutus, E. furnalis, and E. brasiliensis,
and found that the best characters to characterize the species are the length of the
mandible and the length of the mandibular toothrow, but they cannot distinguish all
specimens. Other than a complex linear discriminant function (which separates most
populations of these species), Williams found there is no single characteristic that will
distinguish all E. diminutus, E. furnalis, and E. brasiliensis. These three species can all
be caught in the same net in the rain forests along the Río Paraná in eastern Paraguay
(Redford and Eisenberg 1992).
Davis (1966) considered E. fidelis as a junior synonym of E. dorianus, but recognizable
as a subspecies, and regarded E. diminutus as conspecific with E. dorianus, but
recognizable as a subspecies. Williams (1978) also regards E. diminutus and E. fidelis as
being conspecific, and because E. diminutus has priority, this name is used to refer to the
smallest short-haired South American species of Eptesicus.
There are relatively few specimens of E. diminutus, and from widely scattered localities.
Consequently, little is known about individual and secondary variation, and most South
American Eptesicus are poorly characterized (Williams 1978). Barquez, Giannini, and
Mares (1993) suggest that the species is probably scarce.
E. diminutus, also known as the diminutive serotine, or the diminutive brown bat, is the
smallest bat of the South American Eptesicus, and approaches the size of Myotis. The
dorsum and venter are brown, but in some specimens the venter is washed with gray
(Redford and Eisenberg 1992). The species appears to be strongly dimorphic in size,
with females being larger than males (Williams 1978).
In Uruguay this species may be confused with M. albescens but can be distinguished by
the configuration of the external border of the pinna: in M. albescens it is essentially
straight, whereas in E. diminutus it is convex. Its pelage ranges from dark chestnut
brown with an orangish tint dorsally and paler and more yellowish ventrally to dark gray
with pale yellowish tips to the hairs dorsally and dark gray tinted with brown and whitish
ventrally. The flight membranes are dark brown (Redford and Eisenberg 1992; Williams
1978).
In specimens from eastern Argentina the dorsal hairs are bicolored, their bases dark and
their tips light brown; paler ventrally; in specimens from the northwest, dorsal coloration
is dark and the dorsal hairs are unicolored, calcar long, more than twice the length of the
foot; ears rounded; upper incisors unequal in size.
In northwest Argentina, E. diminutus is generally similar to E. furnalis, but smaller
(Barquez, Giannini, and Mares 1993).
Total length, 81-91; tail, 32-37; foot, 5-7; ear, 13-15; forearm, 32-35; weight, 4.9-6.5;
dental formula, 2/3, 1/1, 1/2, 3/3 = 32 (Barquez, Giannini, and Mares 1993).
Distribution
E. diminutus ranges from Venezuela, discontinuously through eastern Brazil, and south to
eastern Paraguay, western Uruguay, and northern Argentina (Redford and Eisenberg
1992).
Ontogeny and Reproduction
The ontogeny and reproduction of E. diminutus are unknown.
Ecology and Behavior
E. diminutus is an insectivore (Barquez, Giannini, and Mares 1993). In northern
Venezuela E. diminutus was collected at 100 m elevation in a mixed habitat of grassland
and deciduous tropical forest (Handley 1967). The natural roosts of E. diminutus are
unknown (Barquez, Giannini, and Mares 1993). In Paraguay has been found roosting in
houses and in trees (Redford and Eisenberg 1992). Barlow (1965) netted individuals in
low, open thorn woodlands. Several trees near the nets contained hollows and were
suspected of harboring small colonies of bats of various species, including perhaps a few
individuals of E. diminutus.
Literature Cited
Barlow, J. C., 1965. Land Mammals from Uruguay: Ecology and Zoogeography. Ph.D.
Dissertation. University of Kansas. 119-122.
Barquez, R. M., N. P. Giannini, and M. A. Mares. Guide to the Bats of Argentina. 1993.
Oklahoma Museum of Natural History. 57.
Davis, W. B. 1966. Review of South American bats of the genus Eptesicus. The
Southwestern Naturalist 11(2):245-274.
Handley, C. O. 1976. Mammals of the Smithsonian Venezuelan Project. Brigham
Young University Science Bulletin, Biological Series 20(5):1-90.
Redford, K. H., and J. F. Eisenberg. Mammals of the Neotropics, Volume 2, The
Southern Cone: Chile, Argentina, Uruguay, Paraguay. 1992. The University of
Chicago Press. 100-101.
Williams, D. F. 1978. Taxonomic and karyologic comments on small brown bats, genus
Eptesicus, from South America. Annals of Carnegie Museum 47(16):361-383.
Reference written by Elizabeth Roznik, Biology 378 student. Edited by Christopher
Yahnke.
Page last updated 08-03-05.