Eptesicus diminutus - Diminutive serotine​

Physical 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.