1

United States

Department of

Agriculture

Forest Service

Northeastern

Research Station

Research Note NE-376

Abstract

In teaching students and technicians how to identify the

skins and skulls of southeastern bats in the field and

laboratory, it was necessary to develop an illustrated key

that makes identification both easy and reliable. Many of

the existing keys are poorly illustrated, include bat

species that are not applicable, and/or contain univariate

discriminatory measurements that can result in

inaccurate identifications. We constructed a key that

allows users to easily and accurately identify the skin and

skulls of 17 bat species that inhabit the Southeastern and

Mid-Atlantic regions (north of central Florida and east of

the Mississippi River).

MICHAEL A. MENZEL is a wildlife biologist with

West Virginia University’s Division of Forestry;

JENNIFER M. MENZEL is a research wildlife biologist

with the USDA Forest Service’s Northeastern Research

Station; STEVEN B. CASTLEBERRY is a wildlife

biologist and assistant professor with the University of

Georgia’s D. B. Warnell School of Forest Resources;

JAMES OZIER is a wildlife biologist with the Georgia

Department of Natural Resources; W. MARK FORD is

a research wildlife biologist with the Northeastern

Research Station; JOHN W. EDWARDS is a wildlife

biologist and assistant professor with West Virginia

University’s Division of Forestry.

Michael A. Menzel

Jennifer M. Menzel

Steven B. Castleberry

James Ozier

W. Mark Ford

John W. Edwards

Illustrated Key to Skins and Skulls

of Bats in the Southeastern and

Mid-Atlantic States
2

There has been renewed research emphasis on the

distribution and natural history of bats in the

Southeastern United States (Menzel et al. 2000). For

example, one-half of the 14 peer-reviewed manuscripts

and 4 technical reports on the natural history of bats in

Georgia have been published within the past 5 years. Yet

numerous questions posed by land managers and

ecologists remain unanswered. One impediment to

expanding research on and monitoring of southeastern

bats was the lack of a reliable key for identifying bats in

the field. Many existing keys contain information about

bat species that are found in the Southeast (Jenkins 1949;

Golley 1962; Barbour and Davis 1969; Hoffmeister

1989; Sealander and Heidt 1990; Schmidley 1991;

Whitaker and Hamilton 1998), but most are difficult to

use or are unreliable because they are poorly illustrated,

require examination of the lower jaw, or contain

univariate discriminatory measurements.

One of the first illustrated keys to the skins and skulls of

southeastern bats was published in The Mammals of

Georgia: A Study of Their Distribution and Functional Role

in the Ecosystem (Golley 1962). Although of some utility,

this key contains morphological measurements that

conflict with measurements in other keys. For example,

The Mammals of Georgia describes the southeastern

myotis (Myotis austroriparius) as having an interorbital

breadth of less than 4 mm, while The Bats of Texas

(Schmidly 1991) describes the interorbital breadth of

southeastern myotis as being more than 4 mm. A recent

quantitative comparison of 19 skull measurements among

six myotid species found in the Southeast revealed that

skulls of southeastern myotids could not be identified

reliably based on any univariate measurement.1

Additionally, our prior experience in teaching students

and field technicians to identify the bats in the

Southeastern and Mid-Atlantic regions using existing keys

suggested that additional illustration of diagnostic

characteristics, such as those of the keeled calcar of the

Indiana bat (Myotis sodalis), would be helpful in

identifying some species. Thus, the need for a wellillustrated, accurate, and simple key to the skins and

skulls of the bats of the Southeast prompted us to develop

the illustrated key presented here.

Developing the Key

In constructing the key, we used measurements from

museum specimens, information from publications about

1

Menzel, M.A.; Boone, J. L.; Menzel, J. M.; Hauge, M.

Mensural discrimination among six southeastern myotids. In

preparation.

Table 1.—Dental formulas for the bats in the Southeastern and Mid-Atlantic regions

(I = Incisors, C = Canines, Pm = Premolars, M = Molars)

Upper teetha Lower teetha Total (x2)

Species I C Pm M I C Pm M

Pipistrellus subflavus 2 1 2 3 3 1 2 3 34

Nycticeius humeralis 1 1 1 3 3 1 2 3 30

Myotis leibii 2 1 3 3 3 1 3 3 38

M. austroriparius 2 1 3 3 3 1 3 3 38

M. septentrionalis 2 1 3 3 3 1 3 3 38

M. lucifugus 2 1 3 3 3 1 3 3 38

M. sodalis 2 1 3 3 3 1 3 3 38

M. grisescens 2 1 3 3 3 1 3 3 38

Lasionycteris noctivagans 2 1 2 3 3 1 3 3 36

Corynorhinus rafinesquii 2 1 2 3 3 1 3 3 36

Corynorhinus townsendii 2 1 2 3 3 1 3 3 36

Lasiurus borealis 1 1 2 3 3 1 2 3 32

L. seminolus 1 1 2 3 3 1 2 3 32

L. intermedius 1 1 1 3 3 1 2 3 30

L. cinereus 1 1 2 3 3 1 2 3 32

Eptesicus fuscus 2 1 1 3 3 1 2 3 32

Tadarida brasiliensis 1 1 2 3 2/3 1 2 3 30/32

a

Number of teeth in each side of jaw.
3

JV

AD

TL

TV

HF

FA

Figure 1.—Standard bat measurements include total

length (TL), tail length (TV), forearm length (FA),

and foot length (HF). The inset illustrates the extent

of fusion in the epiphyseal gap of the finger joints of

adults and juveniles. Adult joints (AD) appear fused

and consist of a single protuberance; juvenile joints

(JV) are not fused (cartilaginous plates remain in the

joints) and consist of two protuberances or a single

protuberance that is larger and more tapered than in

adult joints.

bat morphological characteristics, and data from existing

dichotomous keys (Jenkins 1949; Golley 1962; Barbour

and Davis 1969; Hoffmeister 1989; Schmidley 1991). All

measurements taken exclusively for our key were from

specimens from the Georgia Museum of Natural History

at the University of Georgia. Because the lower jaw often

is damaged or missing from museum skeletal specimens

or skulls found in the field, we constructed our key so

that the lower jaw is not required for identification.

Many existing keys to southeastern bats do not

discriminate between the skulls of eastern red bats

(Lasiurus borealis) and Seminole bats (L. seminolus). We

incorporated distinguishing data on the size of the

protuberance of the lacrimal ridge (shelf), that proved to

be nearly 75-percent accurate (Lowery 1974; Laerm et al.

1999). Not included in The Mammals of Georgia (Golley

1962), we also included discriminatory information on

the eastern small-footed myotis (Myotis leibii) in our key

to the skins. We did not provide information about the

differentiation of the myotids for the skull key. With the

dichotomous key to the skulls presented here, the user can

classify a skull only as belonging to the genus Myotis.

Although the skins of the six Myotis species that are found

in the Southeastern and Mid-Atlantic regions can be

identified accurately using qualitative characteristics or

univariate metrics, myotid skulls cannot be distinguished

reliably using qualitative characteristics, univariate

metrics, or bivariate scattergrams.1

 Skulls of the six

southeastern myotid species can be identified accurately

(96+ percent correct classification) using complex

multivariate techniques such as discriminate function

analysis.

Exclusive of myotids, many bat skulls can be identified by

counting the number of teeth in one upper quadrant

(one-half of the upper jaw) and measuring the greatest

length of the skull (from the posterior-most margin to the

anterior-most portion, not including the incisors) and

comparing these measures to dental formulae of each

species (Table 1) and the skull key.

Locations of six standard body measurements used in

identification — total length (TL), tail length (TV), foot

length (HF), ear length (E), forearm length (FA), and

tragus length (TR) — are illustrated in Figures 1 and 2.

These measurements can be taken on dead specimens

prior to preparation or on live specimens prior to release.

Our key was designed using characteristics and

measurements recorded from adult individuals and may
4

Figure 3.—Contrast between the tail and

uropatagium of the Brazilian free-tailed bat (Tadarida

brasiliensis) and the other 15 species of bats that are

found in the Southeastern and Mid-Atlantic regions.

The tail of the former extends beyond the posterior

margin of the uropatagium (A); the tails of the other

15 bat species are enclosed in the uropatagium (B).

not be reliable for identifying juveniles. Bats can be

placed reliably in juvenile or adult age classes by

examining the extent of epiphyseal-diaphyseal fusion in

the finger joints (Anthony 1988). Cartilaginous plates are

not apparent in the finger joints of adults, which consists

of a single, knobby protuberance (Fig. 1). Cartilaginous

plates are apparent in juvenile finger joints, which consist

of two protuberances with a slight taper between, or a

single protuberance that is much longer and more tapered

at both ends than that in adult joints (Fig. 1). The most

effective way to observe the cartilaginous plates is by

backlighting the wing and looking for semitransparent

sections in the joints of the phalanges.

Key to Bat Skins

1. a. One-third or more of the tail extends beyond

uropatagium (Fig. 3a)—Brazilian free-tailed bat

(Tadarida brasiliensis)

b. Tail does not extend beyond uropatagium or only

slightly (Fig. 3b)—2

2. a. At least one-third of the dorsal surface of

uropatagium furred—3

b. Dorsal surface of uropatagium not furred or slightly

furred at the junction with the body—7

3. a. Pelage black; tips of hairs frosted with white—4

b. Pelage dark red, mahogany, or yellow—5

4. a. Total length more than 120 mm; uropatagium

heavily furred throughout; ear white or yellow with

black rim—hoary bat (Lasiurus cinereus)

b. Total length less than 115 mm; posterior one-third

of uropatagium bare; ear solid black—silver-haired bat

(Lasionycteris noctivagans)

5. a. White shoulder patch absent, yellow coloration,

frosting absent—northern yellow bat (Lasiurus

intermedius)

A

B

E

TR

Figure 2.—Ear (E) and tragus length (TR) measurements.
5

b. White shoulder patch present, red or mahogany

coloration, frosting usually present (except male

Lasiurus borealis)—6

6. a. Pelage bright, brick-red; tips of hair frosted white

(except males); face is light red/yellow—eastern red

bat (Lasiurus borealis)

b. Pelage dark mahogany; tips of hair frosted white;

face is mahogany/red—Seminole bat (Lasiurus

seminolus)

7. a. Ears more than 25 mm long; distinctive pararhinal

glands (large bumps, Fig. 4) on either side of nose—8

b. Ears less than 25 mm long; pararhinal glands not

distinct—9

8. a. Toe hair extending past claws; pelage gray to light

gray or white from tip to base—Rafinesque’s big-eared

bat (Corynorhinus rafinesquii)

b. Toe hair not extending past claws; pelage pale

brown to black with dark base and tips somewhat

buff—Townsend’s big-eared bat (Corynorhinus

townsendii)

9. a. Total length more than 100 mm, forearm more than

40 mm—big brown bat (Eptesicus fuscus)

b. Total length less than 100 mm, forearm less than 40

mm—10

10.a. Tragus (projection within the ear) short, blunt, and

curved (Fig. 5a)—11

b. Tragus long, pointed at tip, and straight (Fig. 5b)—

12

11.a. Dorsal fur tricolored when parted; coloration black

at base, yellowish-brown in the middle and dark

brown at tips; forearm pink and less than 32 mm—

eastern pipistrelle (Pipistrellus subflavus)

pararhinal gland

Figure 4.—Location of the pararhinal

glands on Rafinesque’s big-eared bat

(Corynorhinus rafinesquii).

Figure 5.—The eastern pipistrelle (Pipistrellus subflavus)

and the evening bat (Nycticius humeralis) have a short,

blunt tragus (A); the myotids have a long, pointed,

sharp tragus (B).

A B
6

b. Dorsal fur dark brown; forearm dark and more than

32 mm—evening bat (Nycticeius humeralis)

12.a. Plagiopatagium (wing membrane outside of hind

legs) proximal attachment to tarsus (ankle), well below

the base of the toes; pelage uniformly gray; hairs not

bicolored (Fig. 6a)—gray bat (Myotis grisescens)

b. Plagiopatagium attached to side of foot at the base

of toes; pelage not gray; hairs bicolored (Fig. 6b)—13

13.a. Ear more than 16 mm long; extends more than 2

mm beyond the tip of nose when laid forward—

northern long-eared myotis (Myotis septentrionalis)

b. Ear does not extend beyond the tip of nose when

laid forward—14

14.a. Calcar keeled (Fig. 7a)—15

b. Calcar not keeled (Fig. 7b)—16

15.a. Foot usually more than 7 mm, forearm usually

more than 35 mm; pelage short and wooly; black

mask around eyes absent—Indiana bat (Myotis sodalis)

b. Foot usually less than 7 mm, forearm usually less

than 35 mm; pelage long and glossy; hairs around eyes

black giving the appearance of a black mask—smallfooted myotis (Myotis leibii)

16.a. Tips of hairs are reddish; hair long and glossy—

little brown bat (Myotis lucifugus)

b. Tips of hairs are not reddish; hair short and

wooly—southeastern myotis (Myotis austroriparius)

Figure 6.—In the gray bat (Myotis grisescens), the

plagiopatagium attaches to the tarsus (A). In the other 5

species of myotids that are found in the Southeastern and

Mid-Atlantic regions, the plagiopatagium attaches to the

side of the foot (posterior margin of the metatarsals) at

the base of the toes (B).

Figure 7.—A keeled calcar (A) is characteristic of

Indiana bats (Myotis sodalis) and small-footed myotis

(M. leibii); an unkeeled calcar (B) is characteristic of

little brown (M. lucifugus) and southeastern (M.

austroriparius) myotis.

A

B

A

B
7

A

B

Key to Bat Skulls

1. a. Upper incisors obviously converge at tips (i.e.,

much closer together at tips than at base, Fig. 8a)—

Brazilian free-tailed bat (Tadarida brasiliensis)

b. Upper incisors wider at tip than base, equidistant at

tip and base, or tips slightly converging (Fig. 8b)—2

2. a. There are nine teeth in upper quadrant (one side of

upper jaw)—Myotis spp.

b. Fewer than nine teeth in upper quadrant—3

3. a. Eight teeth in upper quadrant—4

b. Fewer than eight teeth in upper quadrant—7

4. a. Upper incisor bifid (two-cusped)—Rafinesque’s

big-eared bat (Corynorhinus rafinesquii)

b. Upper incisor unicuspid—5

5. a. Greatest length of skull more than 13.5 mm;

rostrum flat with two concavities on dorsal surface—

silver-haired bat (Lasionycteris noctivagans)

b. Rostrum sloped with no concavities on dorsal

surface—6

6. a. Rostrum strongly sloped; greatest length of skull

more than 13 mm—Townsend’s big-eared bat

(Corynorhinus townsendii)

b. Rostrum gently sloped; greatest length of skull less

than 13.5 mm—eastern pipistrelle (Pipistrellus

subflavus)

7. a. Seven teeth in upper quadrant—8

b. Six teeth in upper quadrant—11

8. a. Two upper incisors (one large, one minute)—big

brown bat (Eptesicus fuscus)

b. One upper incisor—9

9. a. Greatest skull length more than 15.5 mm—hoary

bat (Lasiurus cinereus)

b. Greatest skull length less than 15.5 mm—10

Figure 8.—Unlike the upper incisors of other southeastern

bats (B), the upper incisors of the Brazilian free-tailed bat

(Tadarida brasiliensis) converge at the tips (A).
8

10.a. Protuberance of the lacrimal ridge (shelf) well

developed (Fig. 9a)—eastern red bat (Lasiurus borealis)

b. Protuberance of the lacrimal ridge poorly developed

or absent (Fig. 9b)—Seminole bat (Lasiurus seminolus)

11.a. Sagittal crest well developed; greatest length of skull

more than 16 mm—northern yellow bat (Lasiurus

intermedius)

b. Sagittal crest absent or poorly developed; greatest

length of skull less than 16 mm—evening bat

(Nycticeius humeralis)

Acknowledgments

Support for this project was provided by the USDA

Forest Service, West Virginia University’s Arlen G. and

Louise Stone Swiger Fellowship, and the National

Council of the Paper Industry for Air and Stream

Improvement. Figures 1-8 were illustrated by B. Coslick;

figure 9 was illustrated by G. Weis-Gresham. We thank

the numerous students at the University of Georgia who

tested earlier versions of the keys. Cover artwork by John

MacGregor. This project would not have been possible

without the professional support of B. R. Chapman and

the late J. Laerm.

Literature Cited

Anthony, E. L. P. 1988. Age determination in bats. In:

Kunz, T. H., ed. Ecological and behavioral methods for

the study of bats. Washington, DC: Smithsonian

Institute Press. 533 p.

Barbour, R. W.; Davis, W. H. 1969. Bats of America.

Lexington, KY: University Press of Kentucky. 286 p.

Golley, F. B. 1962. Mammals of Georgia. Athens, GA:

University of Georgia Press. 218 p.

Hoffmeister, D. F. 1989. Mammals of Illinois. Urbana,

IL: University of Illinois Press. 348 p.

A

B

Figure 9.—The lacrimal ridge protuberance of the

eastern red bat (Lasiurus borealis) (A) and the

Seminole bat (L. seminolus) (B). The dorsal surface

view of the upper left skull quadrant is depicted.

Note that the two triangular structures at the top are

the upper incisor and the upper canine. The hooked

structure at the lower left section is the anterior-most

section of the zygomatic arch. The lacrimal ridge

protuberance (lacrimal shelf) typically is larger in L.

borealis than in L. seminolus.
9

Jenkins, J. H. 1949. A dichotomous key to the skulls of

the recent land mammals of the southeastern United

States. Athens, GA: University of Georgia. 87 p. M.S.

thesis.

Laerm, J.; Menzel, M. A.; Krishon, D. M.; Boone, J.

1999. Morphological discrimination of the red bat

(Lasiurus borealis) and the Seminole bat (Lasiurus

seminolus). Journal of the Elisha Mitchell Scientific

Society. 115: 131-139.

Lowery, G. H. 1974. The mammals of Louisiana and its

adjacent waters. Kingsport, TN: Louisiana State

University Press. 565 p.

Menzel, M. A.; Chapman, B. R.; Ford, W. M.; Menzel, J.

M.; Laerm, J. 2000. A review of the distribution and

roosting ecology of bats in Georgia. Georgia Journal

of Science 58: 143-178.

Schmidly, D. J. 1991. The bats of Texas. College Station,

TX: Texas A&M University. 188 p.

Sealander, J. A.; Heidt, G. A. 1990. Arkansas mammals.

Fayetteville, AR: University of Arkansas Press. 308 p.

Whitaker, J. O. Jr.; Hamilton, W. J., Jr. 1998. Mammals

of the eastern United States. Ithaca, NY: Cornell

University Press. 583 p.
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