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JINIVERSIT \G.
ILLINOIS LIBRARY
AT URBANA-CHAMPAIGN
NATURAL HIST SURVE’

zo

Distribution, Habitat, and Calling Season
of the Illinois Chorus Frog (Pseudacris streckeri illinoensis)
along the Lower Illinois River

Lauren E. Brown and George B. Rose

Illinois Natural History Survey Biological Notes 132 September 1988

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

RR55784GR-2M~—9-88

US ISSN 0073-490X

The printing of this publication was paid for by the Illinois Department of Transportation.

No charge is made for most publications of the Illinois Natural History Survey, and a list of those publications is available
upon request. Single copies of most publications are available to anyone requesting them. Requests for multiple copies
should be made in writing and should explain the use to be made of the publications. Address correspondence to the Office
of the Chief at the address below.

Illinois Natural History Survey

Natural Resources Building

607 East Peabody Drive

Champaign, Illinois 61820

The cover photograph of a male Illinois chorus frog (Pseudacris streckeri illinoensis) was taken about 24.1 km (15 mi) east of
Havana, Mason County, Illinois, by John C. Murphy.

Graphic Assistance: Molly Scott
Composition: Patty Duzan and Eva Steger

Citation:
Brown, L.E., and G.B. Rose. 1988. Distribution, habitat, and calling season of the Illinois chorus frog (Pseudacris streckeri
ilinoensis) along the lower Illinois River. Ilinois Natural History Survey Biological Notes 132. 13 p.

Distribution, Habitat, and Calling Season of the Illinois Chorus Frog
(Pseudacris streckeri illinoensis) along the Lower Illinois River

Two aspects of the biology of the Illinois chorus frog
Pseudacris streckert illinoensis Smith 1951 are of current
interest. The first concerns its highly unusual forward
burrowing behavior which involves exclusive use of
the forelimbs for digging (Brown et al. 1972). Move-
ments of the forelimbs of the frog are synchronized
like the arms of a human swimmer doing the breast-
stroke. The vast majority of other fossorial species of
salientians dig backwards with their hind feet (Emer-
son 1976). Pseudacris streckeri illinoensis has evolved a
unique set of morphological adaptations that facilitate
forward burrowing: thick forelimbs, enlarged tuber-
cles on the palms of the hands, stout fingers, reduc-
tion of the intercalary cartilage of the fingers to a
wafer-shaped structure, elimination of vertical offset-
ting of the terminal phalanx from the subterminal
phalanx of the fingers by the intercalary cartilage, and
absence of digital pads (Brown et al. 1972; Brown and
Means 1984; Paukstis and Brown 1987). Brown
(1978) demonstrated that this frog can feed while un-
derground, and that ability helps explain the evolu-
tion of the forward burrowing. Underground feeding
is not known to occur among other species of salien-
tians. As a member of the family Hylidae, the highly
fossorial P. streckeri illinoensis is also quite unusual
because of the predominance of arborealism in the
family.

The second major interest in Pseudacris streckeri il-
linoensis Is its rarity. The subspecies has been reported
only in isolated populations in northeastern Arkansas
(Smith 1966), southeastern Missouri (Smith 1955,
1966; Johnson 1987), extreme southern Illinois in
Alexander County (Holman et al. 1964; Brown and
Brown 1973), southwestern Illinois in Madison and
Monroe counties (Axtell and Haskell 1977; Gilbert
1986), and along the east side of the Illinois River in
west-central Illinois in (prior to the initiation of this
study) Morgan, Cass, Menard, Mason, and Tazewell
counties (Smith 1951, 1961, 1966; Moll 1962). Paucity
of specimens and extensive disturbance of habitat led

Dr. Lauren E. Brown is Professor of Vertebrate Zoology,
Department of Biological Sciences, Illinois State University,
Normal; Dr. George B. Rose, formerly Assistant Wildlife
Specialist in the Wildlife Research Section of the Illinois
Natural History Survey, is now Staff Ecologist, Bureau of
Location and Environment, Illinois Department of Trans-
portation, Springfield. Outside referees Dr. Don Moll and
Mr. Gary L. Paukstis read and recommended this paper for
publication in Biological Notes.

Lauren E. Brown and George B. Rose

to the listing of the frog as a state threatened species
by the Illinois Endangered Species Protection Board
(Illinois Department of Conservation 1978; Morris
and Smith 1981). In addition, the U.S. Fish and
Wildlife Service (Bury et al. 1980) recommended a
status survey. More recently, a Notice of Review from
the U.S. Fish and Wildlife Service (Dodd et al. 1985)
indicated that P. streckeri illinoensis is a Category 2
taxon (it may qualify for listing as a federally endan-
gered or threatened species, but further information
is needed to ascertain the status and vulnerability of
the taxon).

In the early 1980s the Illinois Department of
Transportation became concerned that Pseudacris
streckeri illinoensis might occur in the proposed cor-
ridors for several potential Illinois River bridge sites
of the Central Illinois Expressway (FAP 408) where
the corridors cross the Illinois River floodplain in
Scott and Pike counties. Consequently, we conducted
a field survey along the lower Illinois River, primarily
in the spring of 1984. Presented here are data on the
distribution, habitat, and calling season of P. streckeri
illinoensis collected during that survey.

Methods

Because Pseudacris streckeri illinoensis is highly fos-
sorial (Brown 1978), the best time to search for the
frogs is when they come to the surface to breed in the
spring. Males can begin calling in the spring soon
after daytime temperatures are above freezing, and
they sometimes call even when patches of snow re-
main on the ground (L.E. Brown, personal observa-
tions). In this study, field trips were initiated when
weather conditions seemed favorable in the third
week of February and continued until after the breed-
ing season terminated in May. During the main part
of the breeding season, field trips were usually taken
every 2—4 days. Fieldwork was carried out on 25
nights in the spring of 1984: 17, 23, 25 February; 2, 5,
16, 18, 20, 22, 24, 26, 28, 30 March; 1, 3, 5, 7, 10, 12,
15, 17, 19, 23, 30 April; and 9 May. Thus the com-
plete breeding season of the frog was covered and all
choruses in the study area were presumably found.
Two field trips had previously been taken to the area
in 1983 (9 and 11 May), and two were subsequently
taken in 1985 (14 and 19 March).

Listening for the easily detected, species-specific
mating call of the male (Blair 1958a; Blair and Little-

john 1960; Littlejohn and Michaud 1959) provided

2 Illinois Natural History Survey Biological Notes

the means for locating Pseudacris streckeri illinoensis.
The mating call is a short whistle that is repeated rela-
tively rapidly (Figure 1), and it could be detected from
a distance of at least 2.1 km (1.3 mi) when the wind
was not blowing strongly (Brown 1984). We estab-
lished listening stations at or within hearing range of
bodies of water that could serve as potential chorusing
sites on the floodplain of the Illinois River in Scott,
Morgan, Greene, eastern Pike, and southern Cass
counties. Over the course of the study, 748 stops (not
including stops for triangulation) were made at 109
listening stations. A mean of 25.8 stations was visited
per evening in the field (range =9-—5]1 stations). Be-
cause of time constraints, not all stations were visited
in a given evening. After the locations of choruses
were pinpointed, the sites were revisited during day-
light hours to examine the habitat.

Results

Distribution

Historical background. Alfred C. Weed, former
Curator of Ichthyology at the Field Museum of Natu-
ral History in Chicago, collected the first Pseudacris
streckeri ulinoensis in Illinois in September 1922 from
the bottom of the hatchery well at the Meredosia Fish
Hatchery in Morgan County in the northern part of
our study area (Weed 1923). As no hatchery is shown
on the 1928 Meredosia quadrangle map (U.S. Geolog-
ical Survey), we tried to determine its location by con-

KHZ

0 0.2 0.4 0.6 0.8
SEC

No. 132

tacting fisheries personnel. Maurice A. Whitacre,
former State Fish Culturist with the Illinois Depart-
ment of Conservation, collected information on the
history of the state hatchery system shortly before his
retirement, and in his opinion no official state-owned
hatchery ever existed at Meredosia. He explained the
misnomer as follows.

During the late 1800s and early 1900s, the levee
system along the Illinois River was apparently incom-
plete, and periodic flooding carried fishes far out
onto the floodplain. When the water level receded,
these fishes were stranded in smaller bodies of water.
Through a state rescue program these fishes were col-
lected and relocated to various lakes or ponds for tem-
porary holding. Later these fishes were returned to
the Illinois River or distributed to cities, owners of pri-
vate ponds, sportsmen’s clubs, or other organizations
throughout the state. After a number of years, the
ponds and lakes used for temporary holding were re-
ferred to locally as “fish hatcheries.”

The Meredosia area was mentioned as a site of fish
rescue operations in several adminstrative reports of
the state (e.g., Fairbank et al. 1891; Roe and Schmidt
1897; Stratton and Roach 1925; Stratton and Abbey
1928). The 1926—1927 administrative report of the II-
linois Department of Conservation (Stratton and
Abbey 1928, p. 140) referred to a fish rescue station at
Meredosia Bay (Meredosia Lake) north of Meredosia.
These references and Whitacre’s information suggest
that this site may have been where Weed collected

1.0 1.2 1.4 1.6

FiGuRE 1. Audiospectrogram (narrow band) of three mating calls of a male Illinois chorus frog (Pseudacris streckeri illinoen-
sts) recorded by L.E. Brown on 7 April 1970 in a ditch on the north side of the Saidora—Snicarte Road 2.9 km (1.8 mi) west of
its junction with Illinois State Route 78, Section 11, Lynchburg Township, Mason County, Illinois. Frequency (in kilohertz) is
along the vertical axis; time (in seconds) is along the horizontal axis. Cloacal temperature = 11.6°C; air tempera-
ture = 11.6°C; water temperature = 11.8°C (the male was calling in the water). Snout-vent length = 41 mm (measured alive).

Photograph by Gerald B. Liebenstein.

September 1988

Pseudacris streckeri illinoensis. We suspect that the
center of operations for the rescue station was located
on the southern end of the lake on the east side be-
cause the 1928 Meredosia quadrangle map shows a
number of buildings in that area.

Weed (1923) noted that the specimen he collected
(Figure 2) had a “short, thick body,” and he referred it
to the species Pseudacris feriarum (upland chorus frog).
He also stated that it corresponded well with Cope’s
(1889) first color description for Chorophilus feriarum
brachyphonus from near the Kiskiminitas River in west-
ern Pennsylvania. Walker (1932) examined Weed’s
specimen during the course of research in Ohio that
recognized the mountain chorus frog Pseudacris
brachyphona as a valid species. Walker stated that the
specimen was not brachyphona, but he did not identify
Weed’s specimen to species, possibly because no name

Brown and Rose: Illinois Chorus Frog (Pseudacris streckeri illinoensis) 3

was available for the specimen at that time. The fol-
lowing year (1933), Wright and Wright described
Pseudacris streckeri (Strecker’s chorus frog) as a new
species from the southern United States. Walker then
recognized that Weed’s specimen was P. streckeri, and
he later encouraged Philip W. Smith (late former
Head of the Section of Faunistic Surveys and Insect
Identification at the Illinois Natural History Survey)
to investigate the Meredosia area (Smith 1951).
Weed’s specimen (FMNH 3266) was examined by
Smith (and later by L.E. Brown in the early 1970s and
again in 1985). The specimen is a small (snout-vent
length=28 mm, measured by L.E. Brown in 1985),
sexually immature subadult that was emaciated when
originally preserved (Figure 2). Because of its size and
condition, it is superficially more similar in appear-
ance to Pseudacris brachyphona and P. triseriata feriarum

FIGURE 2. Preserved specimens of Illinois chorus frogs (Pseudacris streckeri illinoensis) representing the older distributional
records from Morgan County in the northern part of the study area. On the left, the first specimen collected in Illinois,
FMNH 3266 (paratype; sexually immature; snout-vent length = 28 mm, measured in 1985). This specimen was collected in
1922 at the Meredosia Fish Hatchery, Meredosia, Illinois, by A.C. Weed. On the right, INHS 5982 (holotype; male; snout-
vent length = 39 mm, measured in 1985), collected “three miles north of Meredosia” in 1950 by students in a herpetology
class from the University of Illinois. Photograph by Gerald B. Liebenstein.

4 Illinois Natural History Survey Biological Notes

than are more normal appearing Pseudacris streckeri il-
linoensis. However, Weed’s specimen is definitely P.
streckert ullinoensis.

Smith’s fieldwork with colleagues and students led
to his subspecies description of Pseudacris streckeri il-
linoensis in 1951. The holotype (INHS 5982, Figure 2)
was collected in 1950 on a highway “three miles north
of Meredosia, Morgan County,” by students in a her-
petology class from the University of Illinois (Smith
1951). That mileage designation would place the type
locality north of Morgan County in Meredosia Lake
or on Meredosia Island in southwestern Cass County.
However, only an unimproved roadway on Meredosia
Island, mostly in Cass County, is present in that re-
mote area. Further details on the type locality were
not provided by the students (P. Smith, personal com-
munication). The only road in the general area of the
type locality that can be considered a highway is U.S.
Route 67/Illinois State Route 100, which runs through
the area in a north—south direction and is 3.7 km (2.3
mi) by quadrangle map east of Meredosia. Thus, the
holotype may well have been collected on that high-
way northeast of Meredosia. (Several choruses were
found near that area during our study.)

New records. We found 36 new locations of
choruses of Pseudacris streckert illinoensis on the flood-
plain on the east side of the Illinois River in Scott,
Morgan, and extreme southern Cass counties (Figure
3). Locations | and 2 are in Cass County, 3—9 in Mor-
gan County, and 10—36 in Scott County. Specific loca-
tions are as follows:

. SW 4, SW V4, Sec. 36, T17N, RISW

. SW 4, SE 4, Sec. 36, T17N, RI3W

. NW, NW %, Sec. 6, TION, R12W

. SS’, NE 4, Sec. 11, & SE %4, Sec. 11, TION,

RI3W

5. NW 4, SW V4, Sec. 27, TI6N, RI3W

6. NW 4, SW V4, Sec. 26, TI6N, RI3W

7. SW 4, SE V4, Sec. 25, TI6N, RIS W

8. NE 4, SW , Sec. 36, TI6N, RI3W
9
0

em OF ND

. SW 4, & SE 4, SE V4, Sec. 34, TI6N, RI3W
. NW 4, Sec. 6 (1,890 m [6,200 ft] north of
south line of Sec. 6, and 838 m [2,750 ft] west
of east line of Sec. 6; this is an irregular sec-
tion), T1I5N, RI3W
11. SW “4, NW 4, Sec. 4 (914 and 1,181 m [3,000
and 3,875 ft] north of south line of Sec. 4, and
30 m [100 ft] east of west line of Sec. 4; this is
an irregular section), T15N, RI3W
12. SE Ys, NW V4, Sec. 6, & NW 4, SE 4, Sec. 6
(869 m [2,850 ft] north of south line of Sec. 6
and 823 m [2,700 ft] west of east line of Sec. 6;
and 762 m [2,500 ft] north of south line of
Sec. 6 and 686 m [2,250 ft] west of east line of
Sec. 6; this is an irregular section), T15N,
R13W
13. SW A, NW 4, Sec. 7, TI5N, RI3W

No. 132

14. SW 4, NW 4, Sec. 8, TI5N, RI3W

15. NE 4, NW 4, Sec. 13, TI5N, RI4W

16. SW 4, NE 4, Sec. 24, TI5N, RI4W

17. SE “4, SE 4, Sec. 24, & SW 14, SE 4, Sec. 24,
TI5N, RI4W

18. SE 4, SE 4, Sec. 24, TI5N, RI4W

19. SE%, NW 4, Sec. 30, TI5N, RIS W

20. SE 14, SE 4, Sec. 25, TI5N, RI4W

21. SW, NW 4, Sec. 31, TI5N, RIZW

22. SE 4, NE 4, Sec. 31, TI5N, RI3SW

23. NE 4, SW 4, Sec. 31, & SE 4, NW 4, Sec.
31, TI5N, RI3W

24. SE 4, NE 4, Sec. 1, & NE 4, SE 4, Sec. 1,
TIA4N, R14W

25. SE 4, SE “4, Sec. 1, TI4N, RI4W

26. E Ya, SW 4, Sec. 8, & W 2, SE 4, Sec. 8,
TI4N, RI3W

27. SW 4, NE 4, Sec. 19, T14N, RI3W

28. SEs, NW 4, Sec. 21, T14N, RISW

29. NW 4, NW \, Sec. 27, T14N, RI3ZW

30. NW 14, SW 4; Sec. 29, T14N, RI3W

31. NE Ys, SW 4, Sec. 27, T14N, RI3W

32. SW 4, SW 4, Sec. 26, TISN, RI4W

33. NE “4, NE 4, Sec. 3, TI3N, RI3W

34. NW 14, SE 4, Sec. 15, T13N, RI3W

35. SE 4, SE V4, Sec. 15, TI3N, RI3SW

36. NW 14, NW \, Sec. 7, TI4N, RI3ZW

We did not find Pseudacris streckeri illinoensis in the
Pike County portion of our study area (on the flood-
plain west of the Illinois River from Valley City to
Florence) even though we surveyed that area fre-
quently. The limited habitat available there is quite
disturbed (see Environmental disruption).

We made several field trips to the southern part of
our study area (southern Scott County and Greene
County) where sand is much less common. On 10 and
12 April 1984, we surveyed the floodplain, stopping
to listen every 0.8 km (0.5 mi) along the Hillview
Blacktop between the southernmost locality record in
southern Scott County (Figure 3) and Bucks Branch
in northern Greene County, but we heard no Pseuda-
cris streckeri illinoensis. On 17 April 1984, we visited
three locations further south in Greene County on the
floodplain in Section 32, T11N, R13W, in Section 17,
TION, R13W, and in sections 29 and 32, TION,
R13W, all in Bluffdale Township. These areas are
designated as having sandpits on the 1980 Kampsville
quadrangle map (U.S. Geological Survey). No P.
streckeri wllinoensis were heard, but the peak of the call-
ing season had passed. In the following year on 14
and 19 March 1985, we returned to our study area in
Scott and Greene counties. Pseudacris streckeri illinoen-
sts were calling vigorously at several localities in Scott
County. When we went south of Scott County on 19
March 1985, however, and visited an area in Section
31, T12N, R13W, in Patterson Township, Greene
County (a pond and flooded ditch in an area desig-

September 1988

nated as a low-level sand terrace on Plate 7 of Willman
1973), we heard no P. streckeri illinoensis.

When our study was nearing completion, Moehn
(1984) reported the first locality for Pseudacris streckeri
illinoensis from Scott County: “2.8 km S intersection of
US Hwy 54 and Hillview Blacktop.” Loren D. Moehn

| |
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aa }
Se sass
~ F Woped
LA ‘

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eS 1

se, La
aces j ie f
Fi ~ ; i

f mak 104) oa]
qgMORGANTR me ite
Scott FRUN 7

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a a GraveT

Sandor
coms TI
4) he Bon

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FiGuRE 3. New distributional records (larger closed circles)
for the Illinois chorus frog (Pseudacris streckeri illinoensis) on
the floodplain of the Illinois River in Cass, Morgan, and
Scott counties, Illinois. Prepared from a portion of a U.S.
Geological Survey map (Quincy NJ 15-3; 1956, revised
1980). Photograph by Gerald B. Liebenstein.

Brown and Rose: Illinois Chorus Frog (Pseudacris streckeri illinoensis) 5

(personal communication) clarified this location; it oc-
curs near one of the choruses we found 2.5 km (by
map) south of the intersection of U.S. Route 36 and
the Hillview Blacktop (Figure 3). (The highway per-
pendicular to the Hillview Blacktop in Scott County
was formerly known as U.S. routes 54 and 36 but is
now designated only as U.S. Route 36.)

Habitat

Availability of sand as a substrate. Brown et al.
(1972) demonstrated through discrimination experi-
ments that Pseudacris streckeri illinoensis had a highly
significant choice of sand for burrowing rather than
black prairie sod. Sod was chosen in only 3 of 50 trials,
and in those three instances the frogs were unable to
burrow because of their unusual method of digging;
consequently, they remained on the surface. Smith
(1966), Brown and Brown (1973), and Axtell and
Haskell (1977) also found that P. streckeri illinoensis is
restricted to areas in the Midwest that have sand sub-
strates. In Mason County to the north @€.our study
area, sand and sandy soils predominate. Our study
area, however, is a mosaic of sand and sandy soils
along with soils that have a higher content of clay, silt,
and/or organic material.

Origin of sand areas in the study area. The areas
of sand in our study area are Pleistocene alluvial sands
deposited by glacial meltwater about 14,000 years ago
(Cote et al. 1970). The sand ridges are a series of rem-
nants of eroded sandbars of the Bath Terrace (Cote et
al. 1970; Willman and Frye 1970). The Illinois Valley
was a major meltwater channel during the Pleis-
tocene. When the Wisconsinan glacier was standing
behind the Valparaiso Moraine about 14,000 years
ago, large quantities of ponded meltwater poured
down the Illinois Valley in a great flood. In the vicin-
ity of the study area, the valley filled to the level of the
Bath Terrace with eroded sand and gravel from up-
stream. Subsequently the river deepened its channel,
cut away part of the fill, and formed the Bath Ter-
race. Later overflow (about 10,000 years ago) further
eroded the valley to as much as 15.2 m (50 ft) below
the present level. During the past 7,000 years the river
has deposited sediment, thereby filling the valley to its
present level (Cote et al. 1970).

Calling sites in relation to Pleistocene deposits.
Thirty-three of the 36 calling sites identified in this
study were on or near (within 800 m, usually much
less) terrace deposits of the Mackinaw Member (A.
Goodfield, personal communication) of the Henry
Formation (Willman 1973). Four of these 33 sites
were clearly located on Henry Formation deposits;
the remaining 29 were either on Henry Formation de-
posits or on nearby Cahokia Alluvium. Only 3 calling
sites that were located on Cahokia Alluvium were
more than 800 m from Henry Formation deposits.
The Henry Formation is composed mostly of sand
and gravel, and “south of Peoria the low-terrace rem-

6 Illinois Natural History Survey Biological Notes

nants are largely pebbly sand” (Willman 1973).
Cahokia Alluvium, on the other hand, is predomi-
nantly “poorly sorted sandy or clayey silt,” although it
occasionally “contains lenses of silty sand” (Willman
1973). The use of sand lenses by Pseudacris streckeri il-
linoensis has been documented by Axtell and Haskell
(1977), who reported finding three P. streckert ullinoen-
sts in “lenticular sand deposits (ca. three meters wide
by 20 m long).”

Calling sites in relation to soil type. Table | lists
the soils present (based on preliminary soil maps from
the U.S. Soil Conservation Service) at each of the 36
calling sites. Ten of the sites were located on soils de-
scribed by the U.S. Soil Conservation Service as
“sand” (which includes “loamy sand”), and another 9
were on soils described as “sandy loam.” The remain-
ing 17 were on nonsandy soils described as loam, silt
loam, silty clay loam, clay loam, or silty clay. All but 7
of the 36 calling sites, however, were within 200 m of
sand, but only 3 of these 7 were more than 200 m
from sandy soil.

Aquatic characterization of calling sites. Pseuda-
cris strecker ulinoensis called at several types of aquatic
sites. The most common (27 of 36 choruses, 75.0%)
were flooded depressions in fields. These sites varied
and were further characterized by one or more of the
following: small marshlike area, cattle or hog pasture,
tilled field, waterway (lentic), flooded drainage ditch
(lentic) in a field, roadside ditch (lentic) flooded into a
field, and pond flooded into a field. Other aquatic
calling habitats included: ditches (lentic) beside or
near roads (4 choruses, 11.1%); pits resulting from
sand mining (2 choruses, 5.6%); permanent pond (1
chorus, 2.8%); pool created by excavations to build a
levee (1 chorus, 2.8%); and retaining basin for a
chemical or water storage tank (1 chorus, 2.8%). All
sites except for the two ponds were probably ephem-
eral, and all sites were lentic. These types of calling
sites were not unique for P. streckeri illinoensis as other
local species of salientians also used these habitats.
Flooded depressions in fields were probably the most
prevalent type of suitable calling habitat present, and
their greater use by P. streckert illinoensis probably re-
flected availability rather than preference over other
types of calling habitats utilized.

No mating calls were heard at sites with lotic envi-
ronments such as ditches with moving water, creeks,
and larger rivers including the Illinois River. Nor did
we hear Pseudacris streckeri illinoensis at larger flood-
plain lakes.

Environmental disruption. A number of habitat
disruptions were found in our study area, and these
may have a negative effect on populations of Pseuda-
cris streckeri illinoensis. The most conspicuous environ-
mental modification is intensive agriculture. Tilling
the soil, moving heavy equipment over the land, com-
paction of soil, and applying agricultural chemicals

No. 132

(insecticides, herbicides, and anhydrous ammonia and
other fertilizers) could be detrimental. However, P.
streckert illinoensis is probably fossorial throughout
much of the year, and its breeding period frequently
occurs before many agricultural activities are initiated
in the spring. The presence of many choruses in fields
also suggests that P. streckeri illinoensis tolerates ag-
riculture or that agricultural practices do not conflict
temporally with its activities. The commonly used her-
bicide Atrazine has been shown to be lethal to frog
eggs in England (Hazelwood 1970). Runoff of her-
bicides into aquatic breeding sites may thus represent
a potential threat to P. streckeri allinoensis.

Thousands of hogs are raised on the sandy areas
in our study area. Their manure pollutes both soil and
water, and their activities denude the soil of vegeta-
tion (Figure 4). It is also likely that Pseudacris streckert
illinoensis are eaten when uncovered by rooting hogs.

The construction of levees along the Illinois River
and associated factors (fast movement of water, pro-
longed inundation in the spring, extensive wave pro-
duction by the many barges, floating debris, water
pollution) provide an environment along the base of
the bluffs in Pike County that does not seem condu-
cive to breeding or habitation by Pseudacris streckeri il-
linoensis. The floodplain of the Illinois River has also
been considerably altered in other ways by the pres-
ence of many levees and drainage ditches (Bellrose et
al. 1983; Brown and Moll 1979; Parmalee and Loomis
1969). Wetlands have been drained for agricultural
purposes and other areas that were probably only sea-
sonally inundated are now permanently flooded
lakes. The consequence of these habitat modifications
for P. streckeri illinoensis is unclear, but they may not
have had a long-term detrimental effect.

Pseudacris streckert illinoensis could be killed by vehi-
cles on the roads in our study area. However, except
for major highways, vehicular traffic is rather light.
We never encountered specimens on roads in the
many hours we spent in the field during this study.
However, the holotype was collected on a highway
(Smith 1951), and other specimens have been seen on
a road in Missouri (Smith 1955). Furthermore, G.
Paukstis (personal communication) encountered
road-killed P. streckeri illinoensis in Illinois. The con-
struction of highways often results in ditches and de-
pressions that accumulate water and these can serve as
breeding sites. In 1972 a vigorous chorus of P. strecken
ilinoensis was encountered in a water-filled depression
within the cloverleaf of the intersection of U.S. High-
way 62 and Interstate Highway 55 just east of Sikes-
ton, Missouri (L.E. Brown, personal observation). On
the other side of I-55, choruses were found in three
years in a marshy depression not far from the high-
way. Both breeding sites may have been created by the
construction of the bridge and access roads at the in-
tersection. On the negative side, however, vehicular

September 1988

traffic releases heavy metals and other toxins into the
environment, and these could contaminate breeding
sites adjacent to highways.

The physical process of mining sand (Figures 5
and 6) could kill Pseudacris streckeri illinoensis and alter
breeding sites. Three choruses in our study occurred
on or adjacent to sand ridges where sand had been

Brown and Rose: Illinois Chorus Frog (Pseudacris streckeri illinoensis) |

mined in the past. One chorus was located on top of a
sand ridge and the site was quite disturbed (Figure 5).
Considerable rubbish had been dumped in the area
and gravel had been hauled in to stabilize the sand for
the movement of heavy vehicles. Extensive sand min-
ing produced numerous pits that partially filled with
water and were used as calling sites. It might be pre-

TABLE 1. Distance from each chorus location of Illinois chorus frogs (Pseudacris streckeri illinoensis) to nearest sand and
nearest other sandy soil. Soil types are given for the location of each chorus, for nearest sand, and for nearest other sandy
soil. Data extracted from preliminary soil maps of the U.S. Soil Conservation Service.

Nearest sand (S) or

Chorus Soil type(s)
identification at location Distance
number of chorus” (m)
1 7302 75(S)
2 206 50(S)
3 200 O(SS)
4 302 50(S)
5 54B O(S)
6 682A 150(SS)
1; 81 25(S)
8 81 25(S)
9 70, 302 50(S)
10 682A 25(SS)
11 180, 302 25, 100(S)°
12 87 0(SS)
13 49, 302 O(S)
14 172A, 200 O(SS)
15 87, 302 O(SS)
16 200 O(SS)
17 54B O(S)
18 54B O(S)
19 26 25(S)
20 26, 682A 50(SS)
21 49 O(S)
22 200 O(SS)
23 49, 682A 0(S)
24 7070 425(SS)
25 26 100(SS)
26 26, 71, 180, 200 O(S)
27 71 250(S)
28 54D O(S)
29 862 O(S)
30 71, 302 50(SS)
31 54B O(S)
32 150B, 302 O(SS)
33 49 0(S)
34 7070 275(S)
35 26 75(S)
36 200 (SS)

nearest other sandy soil (SS)

Nearest sand”
Soil Distance Soil
type(s)” (m) type(s)”

54B = -
54B =

200 100
88B = -

87 125
88B ~ -
87 100, 150° 588
49 - -

172A, 200 ais 1 \P-b): 49
87 500
200 50

200 1600
200 800
54B, 88B, 200 -

200 600

“When sandy soil was nearer than sand to a given chorus, the nearest sand is listed in these columns.
g

»Soil types are indicated as follows.

Sands: Other sandy soils:
49 Watseka loamy sand 87
54B Plainfield loamy sand, 2—-7% slopes
54D Plainfield loamy sand, 7—15% slopes
88B Sparta loamy sand, 1—-6% slopes 200 Oriosandy loam
588 Spartaloamy sand, loamy substratum Other soils:

862 Sandpit 26 = Wagner siltloam

= Sand spot 70

Dickinson sandy loam
150B Onarga fine sandy loam, 2—5% slopes 180
172A Hoopeston sandy loam, 0—3% slopes 206

Beaucoup silty clay loam

71 Darwin silty clay

81 Littleton silt loam

Dupo silt loam

Thorpsiltloam

302. Ambrawclay loam

682A Medway loam, 0—3% slopes

7070 Beaucoup silty clay loam, frequently flooded
7302 Ambraw loam or silty clay loam, rarely flooded

“The three choruses for which two distances are given are choruses that were divided into two parts, the centers of the two parts being as
much as 280 m apart. Two of these choruses were divided by Coon Run Creek.

8 Illinois Natural History Survey Biological Notes No. 132

FiGureE 4. Habitat modification due to hog raising on a sand ridge in Scott County, Illinois. Note that the hog pen is de-
nuded of vegetation. The dead trees in the area adjacent to the pen were probably killed earlier by hogs. The fertile, level
land (with more clay, silt, and/or organic matter) in the foreground is planted in corn. Illinois chorus frogs (Pseudacnis streckert
illinoensis) were heard calling in the springs of 1984 and 1985 not far from this site. Photograph taken on 30 August 1985 by
Kevin J. Tarrant.

FiGuRE 5. Habitat modification due to sand mining on a sand ridge in Scott County, Illinois. Mining has apparently been
carried out periodically for a number of years at this site. Illinois chorus frogs (Pseudacris streckeri illinoensis) were heard call-
ing in ephemeral pools at this site in 1984. Photograph taken on 30 August 1985 (rain had occurred the previous day) by
Kevin J. Tarrant.

September 1988

sumed that because sand mining provided additional
breeding sites, it promotes conservation of P. streckert
illinoensis. However, a number of the sandpits were
dried up in the spring of 1984 before fieldwork in
that year was concluded, and any tadpoles of P. streck-
ert illinoensis present may have died before they had a
chance to metamorphose. We first heard calling males
at this site on 28 March 1984, but a number of the pits
had dried up by 19 April 1984. Taubert et al. (not
dated) estimated that 35—50 days are required for de-
velopment of a tadpole from egg to metamorphosed
juvenile, and thus the sandpit breeding pools may not
retain water long enough for tadpoles to metamor-
phose. Although the ecological characteristics of an
adequate breeding site for P. streckeri illinoensis are un-
clear, aquatic sites over soil with a high content of clay,
silt, and/or organic material may be better because
surface water would be retained longer.

Another chorus also is of particular interest. The
sand ridge associated with it has been mined since at
least 1980 (the site is marked by a symbol for a gravel,
sand, clay, or borrow pit and the word “sandpit” on
the 1980 Bedford quadrangle map), and the recrea-
tional use of ATVs has also disturbed the ridge. On 1
May 1983 Loren D. Moehn found a chorus of approx-
imately ten males calling on top of the ridge (Moehn
1984; Moehn, personal communication). Later in
1983 the aquatic site on the sand ridge was destroyed

Brown and Rose: Illinois Chorus Frog (Pseudacris streckeri illinoensis) 9

by sand mining (Moehn, personal communication).
On 28 March 1984 we stopped at the site. Pseudacris
streckert illinoensis were not calling on the sand ridge,
but a chorus of approximately 25 males was found in
a wide, flooded ditch between the sand ridge and the
nearby Hillview Blacktop (third-most southerly local-
ity in Figure 3). The following spring, on 14 and 19
March 1985, we revisited the area and estimated that
25 and 10 males, respectively, were calling in the same
ditch. The soil at the new site has considerably more
clay, silt, and/or organic matter and hence a greater
capacity to retain surface water. The proximity of the
site to the road, however, subjects dispersing, newly
metamorphosed P. streckeri illinoensis to danger from
vehicular traffic.

Other types of habitat modification that may
threaten Pseudacris streckeri illinoensis in our study area
include trash dumps, a junkyard, development adja-
cent to towns, burning of vegetation around calling
sites, development of chemical storage facilities, and
bulldozing to remove trees and improve drainage.

In spite of actual and potential environmental
threats to Pseudacris streckeri illinoensis, considerable
habitat for the animal remains in our study area.
Much of the land on the sand ridges and other sandy
areas is wooded and not too disturbed. These areas
probably can provide suitable habitat for the frog.

FiGure 6. Sand mining initiated in 1985 on a sand ridge in Scott County, Illinois. Note tracks of ATVs on the slope to the
right of and in front of the end loader. Illinois chorus frogs (Pseudacris streckeri illinoensis) were heard calling adjacent to this
site in the springs of 1984 and 1985. Photograph taken on 30 August 1985 by Kevin ]. Tarrant.

10 Illinois Natural History Survey Biological Notes

Calling Season

On 22 March 1984, when patches of snow were
still evident on the sides of drainage ditches, we heard
the first Pseudacris streckeri illinoensis calling in the
northern part of the study area just north of the Cass/
Morgan county line. Calling was intermittent and only
two or three males were vocalizing at this site. Pseuda-
cris streckert illinoensis were heard nowhere else in the
study area. Heavy rain fell during the evening of 24
March 1984 and calling was more extensive at several
locations in the study area. The last calling was heard
on 23 April 1984 at several localities in Scott County.
Calling may have continued for a few days after 23
April when we were not in the field, but by 30 April
and 9 May 1984 (our next nights in the field) calling
had ceased. Thus, the calling season was at least 33
days in length.

Pseudacris streckeri illinoensis were vocalizing on
each of the 15 nights we were in the field during the
calling season, but the number of males calling in each
chorus varied from night to night and not every
chorus was active every night. However, males were
heard in two of the larger choruses in Scott County
almost every night we were in the field during the
calling season. The peak period of calling activity
seemed to be 1—5 April 1984. During that period,
males also vocalized during daylight hours—a phe-
nomenon not noted earlier or later in the calling sea-
son. As the end of the calling season approached,
fewer calling males seemed to be present and breed-
ing may have diminished.

Discussion

Our study uncovered far more new localities for
Pseudacris streckeri illinoensis than have been reported
in any previous publication. Indeed, the 36 choruses
we found represent a greater number of populations
than the total number heretofore known to be extant.
The most comprehensive previous distributional
study (Taubert et al. not dated) found 18 new local-
ities and a total of 25 extant populations.

Taubert et al. (not dated) found the older histori-
cal populations reported for Morgan, Cass, and
Menard counties to be inactive in 1981. Therefore, no
active localities were known to exist in 1981 along the
Illinois River south of Mason County. Our new rec-
ords, however, firmly establish the presence of
Pseudacnis streckert illinoensis in Scott, Morgan, and Cass
counties. Our findings do not necessarily mean that P.
streckert ullinoensis has undergone a recent population
explosion or range expansion. Rather, we feel that the
populations we found have been in existence for some
time and went undiscovered because the area is re-
mote and was previously little explored for frogs.

The zoogeographic history of Pseudacris streckert
has received comment in various papers. Blair (1958b,

No. 132

1965) presented an argument that southward ad-
vances of glaciers during the Pleistocene forced the
withdrawal of numerous species into refuges in
Mexico and Florida. In various cases the subsequent
isolation and differentiation of these disjuncts re-
sulted in speciation (Blair 1965). The species pair P.
streckert (of the southwestern United States) and the
ornate chorus frog Pseudacris ornata (of the southeast-
ern United States) probably originated in that manner
(Blair 1958b, 1965). This speciational event was consi-
dered to have been initiated prior to the Wisconsinan
glaciation (Blair 1965).

The present occurrence of Pseudacris streckert in
west-central Illinois was thought by Blair (1965) to be
the result of a post-Wisconsinan northeastward dis-
persal from the main portion of the range of the
species in the southwestern United States. Smith
(1957) suggested that P. streckeri was one of several
species adapted to the grasslands of the Great Plains
that later dispersed eastward into the Prairie Penin-
sula of Illinois during the Xerothermic period (6,000
to 4,000 years ago). He envisioned that after the wane
of the Xerothermic and the return of a cooler, moister
climate, P. streckeri was eliminated throughout most of
the Prairie Peninsula except for such favorable re-
fugia as sand prairies.

The discovery of the close association of Pseudacris
streckert illinoensis with sand substrates and the fre-
quent occurrence of the frog on floodplain-like to-
pography led Axtell and Haskell (1977) to suggest a
refinement of Smith’s (1957) Xerothermic hypothesis.
They favored a more southern dispersal avenue for P.
strecker. across Arkansas along the Arkansas River
floodway and up the Mississippi River floodplain to
central Illinois. Isolated distributional records for the
species in Arkansas and Louisiana uncovered by Ax-
tell and Haskell (1977), Turnipseed and Shepherd
(1985), and Fesperman (1986) support a more south-
ern dispersal route.

The timing of these events is, of course, not known
with certainty. However, we feel that the optimal
period for the initial dispersal of the frog through our
study area along the valley of the lower Illinois River
was from 8,000 to 5,000 years ago. Two geological
phenomena were favorable for colonization at that
time. First, the last overflow of glacial meltwater down
the Illinois River valley occurred 10,000 years ago,
and the floor of the valley was as much as 15.2 m (50
ft) below the present level of the floodplain (Cote et al.
1970). Second, the deposition of sediments into the
valley of the Illinois River began 7,000 years ago (Cote
et al. 1970). Consequently, more extensive remnants
of the eroded sand terraces would have been evident
on the surface of the floodplain. Additionally, non-
sandy areas would have been smaller and distances
between sand remnants would have been shorter.
Thus, Pseudacris streckeri could have dispersed

September 1988

through the valley of the lower Illinois River with less
hindrance 8,000 to 5,000 years ago than in earlier or
later times.

The ability of Pseudacris streckeri illinoensis to cross
nonsandy areas is problematic. In regions with exten-
sive sand deposits (e.g., in Mason County), the disper-
sal of the frog may be relatively unhindered. How-
ever, in some other regions (e.g., Scott County), non-
sandy soils occur between many populations of P.
streckert illinoensis on sandy areas. Also, in the southern
part of our study area (Greene County) only minimal
sand is present. Thus, the interesting question arises
as to how the frog disperses from one sand area to
another when the intervening nonsandy regions are
of suboptimal or perhaps even inhospitable habitat.
Fossorialism imposes low vagility and thus dictates a
further hindrance to dispersal. Pseudacris streckeri il-
linoensis has rarely been found on the surface of the
ground outside of the calling season (Smith 1966;
Brown 1978). During the spring calling season when
adult frogs are on the surface, dispersal is possible.
However, mature frogs may be less inclined to leave
established home ranges, and the animals may recog-
nize nearby sand more readily. Dispersal is also possi-
ble soon after metamorphosis. Young frogs would not
yet have established home ranges, and their experi-
ence with sand would be limited or nonexistent. Thus,
they would be more likely to move randomly from
their aquatic habitat to previously unoccupied areas.
Brown and Means (1984) found that recently meta-
morphosed Pseudacris ornata (also a forelimb bur-
rower) in southern Georgia dispersed at least as far as
370 m and possibly as far as 480 m from the breeding
pond where they originated. The location of many of
the breeding sites of P. streckeri illinoensis on nonsandy
substrates adjacent to sand ridges (as seen in Scott
County) may well promote dispersal because random
movement of newly metamorphosed frogs away from
such sites might enhance the colonization of other
more distant isolated sand areas. Thus, even though
P. streckeri illinoensis is probably fossorial (and of low
vagility) throughout much of its life, there are two
periods in the year (during the calling season and,
especially, after metamorphosis) when dispersal is
quite possible.

In the southwestern United States the potential
period of breeding for Strecker’s chorus frog Pseuda-
cris streckeri streckeri is relatively long. Blair (1961)
found males calling as early as 22 October and Wright
and Wright (1949) reported breeding in late May.
Blair (1961) concluded that rain stimulated the activ-
ity of this primarily winter breeder and temperature
was important in determining calling periods.

In the Midwest, the potential period of breeding
of Pseudacris streckeri illinoensis occurs in the spring and
is considerably shorter than that of its southwestern
relative. The typical breeding period in central Illinois
along the Illinois River may be during the month of

Brown and Rose: Illinois Chorus Frog (Pseudacris streckeri illinoensis) 1]

March (Smith 1961). However, the calling season we
observed in 1984 took place from 22 March through
23 April. Standing water was available for breeding
and some rainfall did occur as early as 17 February
1984. Conditions seemed appropriate for calling, and
on 23 February 1984 we heard two small choruses of
striped chorus frogs Pseudacris triseriata (which at
other times frequently called with P. streckeri illinoen-
sis). Intermittent snow storms, sleet, and cold weather,
however, occurred in late February and in the first
half of March. Thus, periodic inhospitable weather
probably delayed the calling season in 1984.

Clearly, Pseudacris streckeri illinoensis was commonly
encountered in our study area. We did not, however,
carry out mark and recapture studies to estimate
population sizes because the time required (probably
at least 2—4 hours each night at each location) would
not have permitted adequate sampling of other listen-
ing stations. Further, it would have been impossible to
satisfy the restrictive conditions of Poole (1974) that
must be fulfilled to assure the validity of statistical esti-
mates of population size (see Brown and Moll 1979).
We did, however, estimate chorus sizes by listening to
the numbers of males calling. In small choruses (fewer
than seven males) our estimates were probably quite
accurate; in larger choruses our estimates were less
precise. In 1984, half of the choruses (n= 18; 50.0%)
were estimated to have a maximum of 1-10 calling
males. Eleven choruses (30.6%) were estimated to
have a maximum of | 1—20 males; 3 choruses (8.3%), a
maximum of 21—30 males; 2 choruses (5.6%), a
maximum of 31—40 males; 1 chorus (2.8%), probably
about 50 males; and | chorus (2.8%), possibly around
100 males. However, the number of males calling in
the choruses varied on different nights. Nonetheless,
the numbers of calling males in many choruses were
relatively small. Additional field surveys in southeast-
ern Missouri, northeastern Arkansas, along the Mis-
sissippi River, and further south along the Illinois
River would help for the determination of whether or
not P. streckert illinoensis should be listed as a federally
threatened or endangered species.

Summary

Thirty-six new distributional records are reported
for the Illinois chorus frog Pseudacris streckeri ilinoen-
sis, a species listed as threatened by the Illinois Endan-
gered Species Protection Board. These records were
collected on the floodplain of the Illinois River in
Morgan, Scott, and southern Cass counties, Illinois,
and represent a greater number of populations than
the total number heretofore known to be extant. The
choruses were found on or not far from sand or sandy
soils. The most typical calling sites were ephemeral,
flooded depressions in fields. No choruses were
found in lotic environments or at larger floodplain
lakes. Substrates at calling sites frequently contained a

12 Illinois Natural History Survey Biological Notes

considerable amount of clay, silt, and/or organic mat-
ter; these soils can hold surface water longer than
permeable yellow sand. Considerable environmental
disruption occurs in the study area, and agricultural
practices (particularly hog raising and the application
of agricultural chemicals) probably pose the greatest
potential threat to the frog. However, considerable
relatively undisturbed habitat remains available for
the frog in our study area, particularly on sand ridges.
The 1984 calling season extended from 22 March until
at least 23 April and peaked from 1—5 April. Inhos-
pitable weather in late February and March probably
delayed the calling season. Although the number of
choruses found in our study area was relatively large,
the numbers of calling males in many choruses were
small. Additional field surveys in other areas are de-
sirable before a determination is made as to whether
or not the Illinois chorus frog should be listed as a
federally threatened or endangered species.

Acknowledgments

We thank J. Brown for her considerable help with
late-night driving and fieldwork; R. Anderson and
J. Slack for enlightening discussion; J.P. Biggers, J.
Brown, A. Goodfield, E. Mockford, C. Perino, and
J. Slack for critically reading all or parts of the manu-
script; R. Inger, H. Marx, and H. Voris for the loan of
specimens (FMNH 3266 and others) from the Field
Museum of Natural History; L. Johnson for the use of
a camera; G. Liebenstein and K. Tarrant for taking
photos; L. Moehn for information on the chorus of
Pseudacris streckeri illinoensis he found in Scott County;
J. Murphy for the cover photo; L. Page for the loan of
INHS 5982 from the Illinois Natural History Survey;
C. Perino and R. Nowack for help with fieldwork; J.
Rowley for obtaining soil maps of the study area; E.
Scoggin for assistance pertaining to Figure 3; the late
P. Smith for correspondence about the holotype; D.
Stewart for information on A. Weed; M. Sweet for
supplying a State Endangered Species Permit to work
on P. streckeri illinoensis; G. Thurow for directing us to
an area where P. streckeri illinoensis could be found in
northwestern Morgan County; and M. Whitacre for
information on the fish rescue program. Primary fi-
nancial support was provided by the Statewide Biolog-
ical Survey Program of the Illinois Department of
Transportation. The Department of Biological Sci-
ences, Illinois State University, provided funds for
photographic services and secretarial help.

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Smith, P.W. 1961. The amphibians and reptiles of Illinois.
Illinois Natural History Survey Bulletin 28:1—298.

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vision of Game and Fish. Pages 82—88 in Seventh ad-
ministrative report of the directors of departments
under the Civil Administrative Code for the year, July 1,
1923, to June 30, 1924. State of Illinois, Springfield.

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[n.d.]. Breeding biology and distribution of the Illinois
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Willman, H.B. 1973. Geology along the Illinois waterway—a
basis for environmental planning. Illinois State Geologi-
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Willman, H.B., and J.C. Frye. 1970. Pleistocene stratigraphy
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1-204.

Wright, A.H., and A.A. Wright. 1949. Handbook of frogs
and toads of the United States and Canada, 3rd ed.
Comstock Publishing Associates, Ithaca, New York.

Wright, A.A., and A.H. Wright. 1933. Handbook of frogs
and toads—the frogs and toads of the United States and
Canada, Ist ed. Comstock Publishing Company, Inc.,
Ithaca, New York.

Manuscripts of high quality dealing with any aspect of natural history will be considered for publication in one of the II-
linois Natural History Survey series: Bulletin, Biological Notes, Circular, and Special Publications. Authors who are not employ-
ees of the Survey are required to pay printing costs. Manuscripts should follow the recommendations of the third edition of
the Council of Biology Editors Style Manual except that journal names in literature cited are to be spelled in full. The Survey ex-
pects to publish only one or two manuscripts by non-Survey authors yearly.

Send three copies of manuscripts to be considered for publication to Office of the Chief, Illinois Natural History Survey,
607 East Peabody Drive, Champaign, Illinois 61820.

\Ilinois Natural History Survey
Natural Resources Building
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A Division of the Illinois Department of Energy and Natural Resources

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