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JINIVERSITY ©.
ILLINOIS LIBRARY
AT URBANA-CHAMPAIGN
NATURAL HIST SURVE’

Distribution, Habitat, and Zoogeography
of the Plains Leopard Frog (Rana bairi) in Illinois

Lauren E. Brown
Michael A. Morris

Illinois Natural History Survey Biological Notes 136
May 1990

Illinois Natural History Survey, Lorin I. Nevling, Chief
A Division of the Illinois Department of Energy and Natural Resources

Printed by authority of the State of Illinois
X05481-2M-5-90
US ISSN 0073-490X

The photograph of a plains leopard frog (Rana blairi) from Spring Lake, Tazewell County, Illinois, used on the cover was
taken by Dr. Douglas W. Whitman.

A catalog of the publications of the Illinois Natural History Survey is available without charge from the address below.
A price list and an order blank are included with the catalog.

Illinois Natural History Survey

Distribution Center

607 East Peabody Drive

Champaign, Illinois 61820

Citation: Brown, L.E., and M.A. Morris. 1990. Distribution, habitat, and zoogeography of the plains leopard frog (Rana blair)
in Illinois. Illinois Natural History Survey Biological Notes 136. 6 p.

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Natural History Survey series: Bulletin, Biological Notes, Circular, and Special Publication. Authors who are not employees of the
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Distribution, Habitat, and Zoogeography
of the Plains Leopard Frog (Rana Dlairi) in Illinois

The early study of leopard frogs (Rana pipiens com-
plex) in Illinois and elsewhere was hampered by
several factors. Most important were (1) overlapping
and confusing morphological and color pattern
variation among the different species, (2) availability
of a number of specific names coupled with a complex
nomenclatural history (Brown et al. 1977), and (3)
lack of knowledge about the nature of reproductive
isolation and cryptic speciation in frogs. Consequently,
little of significance was published on leopard frogs in
Illinois until the appearance of The Amphibians and
Reptiles of Illinois (Smith 1961). Smith recognized two
leopard frog taxa in Illinois: Rana pipiens pipiens in the
northern one-third of the state and Rana pipiens
sphenocephala in the southern one-third of the state.

A wide zone of intergradation was thought to occur
across the center of Illinois. Subsequent research
(Brown and Brown 1972) revealed different “call
types” in Illinois that were considered to represent
distinct species. Other research (summarized by Brown
1973) supported this suggestion, and three sibling
species are now recognized as occurring in Illinois
(northern leopard frog, Rana pipiens Schreber 1782;
southern leopard frog, Rana sphenocephala Cope 1886;
and plains leopard frog, Rana blairi Mecham et al.
1973).

A number of publications (Axtell 1976; Axtell and
Haskell 1977; Brown and Brown 1972; Brown and
Funk 1977; Mecham et al. 1973; Pace 1974; Vogt 1981)
presented distributional information on Rana blair in
Illinois but comprehensive coverage has been lacking.
The objectives of this paper are (1) to present the
results of an in-depth investigation of the distribution
of R. blair‘ in Illinois, (2) to provide information on
the present and probable past habitats occupied by the
species in the state, and (3) to discuss the zoogeogra-
phy of the species.

Dr. Lauren E. Brown is Professor of Vertebrate Zoology,
Department of Biological Sciences, Illinois State University,
Normal; Dr. Michael A. Morris, formerly Assistant Research
Biologist in the Section of Aquatic Biology of the Illinois
Natural History Survey, is now Team Leader, Cuivre Island
Field Station, Western Illinois University, P.O. Box 219,
O'Fallon, Missouri.

Lauren E. Brown and Michael A. Morris

Materials and Methods

Distributional records for Rana blairi were obtained
through examination of preserved specimens and
fieldwork. The collections of the following 17 muse-
ums, academic institutions, and private individuals
were searched for specimens: Chicago Academy of
Sciences, Eastern Illinois University, Edward O. Moll
collection, Field Museum of Natural History, Illinois
Natural History Survey, Illinois State Museum, Illinois
State University, Lauren E. Brown collection, Michael
A. Morris collection, National Museum of Natural
History—Smithsonian Institution, Principia College,
Southern Illinois University at Carbondale, Southern
Illinois University at Edwardsville, University of Illinois
Museum of Natural History, University of Kansas
Museum of Natural History, University of Michigan
Museum of Zoology, and Western Illinois University.

The three species of leopard frogs in Illinois are
distinguished by a combination of morphological
character states: presence or absence of vestigial male
oviducts, and dorsolateral folds continuous or broken
(on one or both sides) just anterior to the thigh and
displaced medially (Table 1; Brown and Brown 1972).
Although displaced dorsolateral folds (Fig. 1) alone
morphologically distinguish Rana blair from R. pipiens
and R. sphenocephala, the possibility of natural hybridi-
zation necessitated that we open the abdomens of
leopard frogs to check for the presence or absence of
vestigial male oviducts.

Fieldwork was carried out from 1968-1989, primar-
ily in central and southern Illinois, although a number
of field trips were taken to northeastern Illinois. Nu-
merous specimens were captured alive or picked up
DOR (dead-on-the-road) and examined.

Table 1. Distinguishing morphological character combina-
tions for the three species of leopard frogs in Illinois.

Dorsolateral Vestigial

Species folds male oviducts

Rana blain displaced absent

Rana pipiens continuous present

Rana sphenocephala continuous absent

z Illinois Natural History Survey Biological Notes

The species-specific mating call of males is an
important isolating mechanism in frogs and toads
(Blair 1958a, 1964). Consequently, listening for the
mating call (Littlejohn and Oldham 1968; Brown and
Brown 1972; Mecham et al. 1973; Dunlap and Kruse
1976) provided a means for us to locate Rana blain.
The mating call (Fig. 2) has been described as sound-
ing like “chuck-chuck-chuck” (Conant 1975). It usually
is relatively low in volume and resembles the pounding
of a nail by a single carpenter in the distance. In
contrast, the mating call of R. pipiens is a “long deep
rattling snore,” and that of R. sphenocephala is a “short

Figure 1. Plains leopard frog (Rana blairi) from Spring Lake,
Tazewell County, Illinois, showing broken dorsolateral fold
that is displaced medially just anterior to the thigh. Photo-
graph by Dr. Douglas W. Whitman.

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No. 136

chuckle-like, guttural trill” (Conant 1975). Quantita-
tively, the much lower pulse rate (average of less than
six pulses per sec below 24°C—Mecham et al. 1973) of
the mating call of R. blairi distinguishes it from the
mating calls of R. pipiens and R. sphenocephala.

Mating calls of Rana blairi were recorded at a
number of locations in central Illinois using a Stancil-
Hoffman Minitape M9 tape recorder with Altec 633A
and Electro-Voice 644 microphones at a speed of 19
cm (7.5 in) per sec. Cloacal, air, and water tempera-
tures were taken with a Schultheis quick-reading ther-
mometer to the nearest 0.1°C immediately after re-
cording calls. A Kay model 6061A Sona-Graph was
used to analyze mating calls.

Distribution

Rana blairi has been found at 194 localities in Illinois.
The species is distributed (Fig. 3) mainly in a wide
band across the middle of the state with a southern
extension along the Mississippi River to extreme
southern Illinois (Alexander County). Smith’s (1961)
zone of intergradation between the two leopard frog
taxa he recognized in Illinois (R. pipiens pipiens and R.
pipiens sphenocephala) shows considerable overlap with
the distribution of R. blair across the center of the
state. We found many of the specimens from this area
that had been examined by Smith (1961) to be R.
blair. Clearly Smith (1961) often considered R. blair as
intergrades between R. pipiens pipiens and R. pipiens
sphenocephala. (L.E.B. came to this conclusion as
distributional data on leopard frogs in Illinois began to
accumulate; P.W. Smith and M.A.M. independently
came to the same conclusion [Morris et al. 1983].)

1.0 1.2 1.4 1.6 1.8

SEC

Figure 2. Audiospectrogram (narrow band) of the mating call of a male plains leopard frog (Rana blair) recorded on 24 April
1970 in a farm pond 3.49 km (2.17 mi) east of U.S. Highway 51 and 0.87 km (0.54 mi) north of McLean County Highway 8 (SW
kk, NW ‘4s, Section 2, T25N R2E), Hudson Township, McLean County, Illinois. Frequency (in kilohertz) is along the vertical axis;
time (in seconds) is along the horizontal axis. The complete first sequence (first four notes) and the initial part of the second
sequence (last two notes) are illustrated. Cloacal temperature = 16.1°C; air temperature = 9.4°C; water temperature = 16.0°C
(the male was calling in the water). Snout-vent length = 68 mm (measured alive). Recorded by L.E. Brown; photographed by
Gerald B. Liebenstein.

May 1990

Rana blair is not panmictic in Illinois, and we have
not found it to be abundant at any locality in spite of
the large number of distributional records (greater
than for any other state). Insufficient appropriate
habitat (see the following section, Habitat) probably is
responsible for this lack of abundance. In contrast, R.
sphenocephala is numerous at many localities in south-
ern Illinois where much of the environment is consid-
erably less disturbed by humans.

Along the northern edge of its range in Illinois,
Rana blair is sympatric at some localities with R.
pipiens. Sympatry appears to be more extensive
between R. blairiand R. sphenocephala than between R.
blairiand R. pipiens. Rana blairiand R. sphenocephala
occur together along the Illinois River in west-central
Illinois, along the Mississippi River in southern Illinois,
and at some localities along the southern edge of the
range of R. blair in central and eastern Illinois.

Habitat

Breeding sites that we found to be commonly utilized
by Rana blairi in Illinois included roadside and drain-
age ditches, marshes, rain pools, flooded areas, farm
ponds, and sometimes lakes. Some sites were ephem-
eral, and all were lentic. Outside the breeding season
we found individuals near the breeding sites as well as
on bottomlands, along creeks, in old fields, and in
variable habitats that often showed past disturbance
(nonagricultural) by humans. We never found R. blain
a great distance from water.

Two major types of environments in Illinois
apparently are not occupied by the species. We never
encountered the frog in mature upland forests or in
tillable fields (e.g., corn, soybeans). One of us (L.E.B.)
has carried out a number of herpetological surveys for
the Illinois Department of Transportation in central
and northeastern IIlinois. These surveys frequently
involved traversing arable land, but Rana blair was
never seen. Rana blairi was also never encountered in
tilled fields by either of us over many years of other
fieldwork in central Illinois. Moreover, K.A. Brown,
L.N. Brown, and G.L. Paukstis (personal communica-
tions) spent a great many days in several different years
roguing and detasseling corn in central Illinois without
coming across R. blairi (although American toads [ Bufo
americanus] were occasionally seen, usually near the
edges of fields). The absence of R. blain from culti-
vated fields could be the result of alteration of the soil
structure through tilling and/or compaction from
heavy farm machinery, application of agricultural
chemicals (anhydrous ammonia and other fertilizers
[see Berger 1989], herbicides [see Hazelwood 1970],
and insecticides), tiling of fields to reduce water
content of the soil, seasonal aridity (particularly mid
through late summer), lack of appropriate cover, or a
combination of these and other factors.

Brown and Morris: Plains Leopard Frog (Rana blair) 3

The devastating effect of the moldboard plow on
soil structure was emphasized by the well-known
agricultural conservationist Louis Bromfield (1955).
The steel moldboard plow was of considerable signifi-
cance in the establishment of agriculture in the
midwestern prairies because it greatly facilitated the
turning of prairie sod (Broehl 1984). Bromfield (1955)
pointed out that the pressing action of the moldboard
plow produces an artificial compacted layer (“hard-
pan”) some 17.8—20.3 cm (7-8 in) below the surface of

Figure 3. Distributional records for the plains leopard frog
(Rana blair’) in Ilinois. Closed circles represent localities for
preserved specimens we examined in museums and collec-
tions and for frogs heard in the field, recorded in the field,
DOR (dead-on-the-road), or caught, examined, and released
in the field. A number of circles represent two or more
records that are too close together to plot separately. Open
circles represent five other literature records and two
unpublished records (based on specimens we did not
examine) that are believed to be valid. The closed triangle
represents a record for R. blain (a museum specimen
examined by us) with locality data that we regard as question-
able. The entire known range of R. blair is shown in the
lower left corner.

4 Illinois Natural History Survey Biological Notes

the soil. The depth is variable depending upon how
deep the plow is set. Bromfield (1955) mentioned a
minimum depth of 5.1 cm (2 in). The typical depth in
central Illinois is 20.3-30.5 cm (8-12 in) at present
(T.E. Alt, personal communication). Much agricultural
land in Illinois has probably been underlaid with
hardpan because of the extensive use of the steel
moldboard plow for well over a century. The hardpan
is 5.1-7.6 cm (2-3 in) thick and is not easily pene-
trated by water and plant roots (Bromfield 1955). Con-
sequently, penetration of this impacted layer by am-
phibians (e.g., Rana blain, Pseudacris triseriata, Amby-
stoma texanum) seems doubtful should these animals
seek subterranean shelter (e.g., for winter hibernation
or to escape desiccation).

The distribution of Rana blair is primarily in the
Great Plains (Brooks 1976; Dixon 1987; Dunlap and
Kruse 1976; Hillis 1981; Lardie 1982; Littlejohn and
Oldham 1968; Lynch 1978; Mecham et al. 1973; Pace
1974; Post and Pettus 1966), with an eastward exten-
sion into the Prairie Peninsula (this paper; Axtell 1976;
Brown and Brown 1972; Johnson 1987; Pace 1974).
Prior to European settlement, this vast area was mainly
prairie and was likely the predominant habitat occu-
pied by R. dblairi. All of the range of R. blair as presently
known in Illinois, except for areas along the Mississippi
and Illinois rivers, occurs within the borders of the
presettlement prairie mapped by Anderson (1970).
Much of the prairie in Illinois was notable for its poor
drainage, which resulted in extensive marshes and
potholes (White 1978); hence it was sometimes called
“muck prairie” (Smith 1961). The Illinois prairies were
mostly unoccupied by humans until the decade
1850-1860 when the precipitous establishment of
railroads facilitated the rapid settlement of the area
(Barrows 1910; Wyman 1988). As late as 1871, prairie
was still common in certain areas of Illinois but by
1883 much had been converted for agricultural use
(Ridgway 1889). The continuing advancement of
agriculture, of course, destroyed nearly the entire
prairie ecosystem in Illinois. The ability of R. blair to
occupy areas peripheral to prairies and intense
agricultural cultivation probably allowed the species to
continue to survive in the state.

Zoogeography
Blair (1958b, 1965) was a foremost proponent of an
influential Pleistocene zoogeographic theory, which
suggested that southward glacial advances caused the
displacement of many warm-adapted, terrestrial,
vertebrate species into refugia in Florida and Mexico.
Rana blairi (or its evolutionary precursor) may have
been one of those taxa that withdrew to the south.
However, the present northern limits of the range of

No. 136

R. blairi (as far north as southern South Dakota—
Dunlap and Kruse 1976) suggest that the species has
considerable cold tolerance, at least in its northern
populations. Thus, the retreat of the entire species
into Mexico during the Pleistocene glaciations seems
unlikely. After the Wisconsinan glaciation, it was
possible for R. blain to expand its range northward in
the Great Plains. Smith (1957) proposed that a num-
ber of prairie-adapted species of the Great Plains
moved eastward into the Prairie Peninsula during the
subsequent Xerothermic Period. Rana blair probably
was one of those species that moved eastward, as
evidenced by its present distribution in the Great
Plains and Prairie Peninsula. However, Pace (1974)
suggested that R. blairi may have made this range
expansion during or after the post-Pleistocene devel-
opment of the Prairie Peninsula. The warm, arid
climate during the Xerothermic would probably have
been unfavorable for major amphibian migrations.
Thus, it seems likely that R. blair moved eastward after
the Xerothermic and after establishment of prairie.

The present extension of the range of Rana blain
south of the Prairie Peninsula along the Mississippi
River in southern Illinois is somewhat puzzling because
Anderson (1970) did not map presettlement prairies
in that area. However, other evidence (R.C. Anderson,
personal communication; Evers 1955; Gleason 1922;
King and Allen 1977; Schroeder 1983; Transeau 1935)
indicates the presence of some prairies along the
Mississippi River in southeastern Missouri and south-
ern Illinois during the Holocene. Thus, the ability of
R. blairi to occupy areas peripheral to prairies, as well
as the presence of scattered prairies, apparently
allowed the species to colonize this area, most likely by
an unusual southerly migration from the Prairie
Peninsula in the mid-Holocene.

Pace (1974) reported two apparently isolated
localities for Rana blair in southeastern Illinois
(“Wabash Co.: 2 mi N of Mount Carmel”) and south-
western Indiana (“Warrick Co.: Scales Lake, near
Boonville”). These localities are, respectively, ca. 1.2
km (0.8 mi) or less SW of the Wabash River, and ca.
17.4 km (10.8 mi) NE of the Ohio River. These popu-
lations may have originated by dispersal of R. blaini
southward from the Prairie Peninsula along the
Wabash River and/or perhaps even northeastward up
the Ohio River from Alexander County in extreme
southern Illinois. Anderson (1970) and Transeau
(1935) reported scattered presettlement prairies in
and adjacent to Wabash County, Illinois, but Lindsey et
al. (1965, 1969) did not recognize any in southwestern
Indiana in or near Warrick County (although presettle-
ment prairies did occur not too far away in adjacent
Illinois—Anderson 1970).

May 1990

Summary

Examination of museum specimens, fieldwork, and
literature records revealed 194 distributional localities
for the plains leopard frog (Rana blair) in Illinois. The
species is distributed in a wide band across the center
of the state with an elongated extension along the
Mississippi River to extreme southern Illinois. Sympa-
try between R. blairi and two other leopard frog species
(Rana pipiens and Rana sphenocephala) occurs at some
localities.

The present distribution of Rana blairi in the Great
Plains and Prairie Peninsula suggests that prairie was
its main habitat prior to European settlement. Rana
blairi presently occupies a variety of habitats (often
showing disturbance by humans) that are peripheral
to arable land. This distribution probably reflects the
nearly complete destruction of the prairie ecosystem
in Illinois by advancing agriculture, which R. blairi
apparently cannot tolerate. We did not find the
species to be abundant at any locality in the state.

Rana blair probably colonized the Prairie Penin-
sula in Illinois after the warm, arid Xerothermic
Period during the Holocene. The ability of R. blair to
occupy areas peripheral to prairies as well as the
presence of scattered prairies during the Holocene
apparently allowed the species to disperse along the
Mississippi River into southern Illinois and southeast-
ern Missouri.

Acknowledgments

We thank T.E. Alt, R.C. Anderson, J.R. Brown, E.L.
Mockford, L.L. Osborne, L.M. Page, G.L. Paukstis, and
J.J. Slack for critically reading all or part of the manu-
script; T.E. Alt, R.C. Anderson, J.R. Brown, and J.J.
Slack for enlightening discussion; R.C. Anderson, D.E.
Birkenholz, and G.B. Rose for bibliographic assistance;
R.W. Axtell (Southern Illinois University at Edwards-
ville), W.J. Beecher and R. Vasile (Chicago Academy of
Sciences), R.A. Brandon (Southern Illinois University
at Carbondale), R.F. Inger, H. Marx, and H.K. Voris
(Field Museum of Natural History), A.G. Kluge
(University of Michigan Museum of Zoology), K.
Livezey, J. Wanamaker, and D.K. Warren (Principia
College), L.R. Maxson and D.M. Smith (University of
Illinois Museum of Natural History), E.O. Moll
(private collection and Eastern Illinois University),
L.M. Page (Illinois Natural History Survey), J.R. Paul
and J.R. Purdue (Illinois State Museum), J.E. Simmons
(University of Kansas Museum of Natural History),
G.R. Thurow (Western Illinois University), and G.R.
Zug (National Museum of Natural History, Smith-
sonian Institution) for allowing us to examine pre-
served specimens under their care; R.A. Brandon and
D.L. Moll (outside referees) for reading and recom-
mending this paper for publication in Biological Notes,

Brown and Morris: Plains Leopard Frog (Rana blairi)

J.R. Brown, L.N. Brown, R.S. Funk, and D.L. Moll for
assistance in examining museum specimens; J.R.
Brown, J.T. Peterson, and G.B. Rose for help with
fieldwork; K.A. Brown, L.N. Brown, and G.L. Paukstis
for supplying information on the occurrence/absence
of frogs and toads in corn fields; N.J. Doss for typing
the manuscript; K.C. Kruse, K.S. Mierzwa, and M.
Redmer for providing locality records from Vermilion,
Will, and Effingham counties, respectively; G.B.
Liebenstein for photographing Figure 2; and D.W.
Whitman for taking the cover photo and Figure 1.
Financial support for some of the fieldwork was
provided by the Illinois Department of Transportation
(Statewide Biological Survey Program) and the Illinois
Department of Conservation. Illinois State University
(Department of Biological Sciences) provided funds
for photographic services and secretarial help.

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No. 136

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