ditches (normally having several feet of water and a lush growth of
aquatic vegetation) that connect inland swamps to the Mississippi
flood-plain but dry up periodically, and in Elkville Lake, an
artificial lake having much aquatic vegetation in shallow areas (_op.
cit._:157). Myers (1927:339) recorded a _spinifer_ from Indiana from a
"tiny brook." In east-central Illinois P. W. Smith (1947:39) recorded
_spinifer_ in mud-bottomed dredge ditches, lakes, ponds, small streams
and rivers, whereas _muticus_ was found to prefer rivers having clean,
sandy bottoms and was not taken from lakes or small streams. This
restriction in habitat preference of _muticus_ is again emphasized by
Smith and Minton (1957:346) who wrote that in Illinois and Indiana,
_muticus_ "generally avoids lakes and minor streams." Weed (1923:48),
however, recorded _muticus_ (and _spinifer_) from Meredosia Bay,
Illinois, presumably a broad, shallow, muddy ox-bow lake of the
Illinois River.
In Minnesota, _spinifer_ has been taken from the Mississippi River,
which is described as fairly swift having a fluctuating water level,
sandy islands, mud banks, a bed of pebbles and large boulders, and
abundant crawfish (Breckenridge, 1955:5). In Michigan, Edgren
(1942:180) recorded _spinifer_ from a "very small muck-bottomed lake."
Evans and Roecker (1951:69) recorded _spinifer_ from Long Point, Lake
Ontario, which is a "broad sand spit, straight on the lakeward side
but irregular with wet flats and lagoons on the bayside."
In Kansas, Brumwell (1951:207-08) found "mostly young [_muticus_] ...
in the old ponds left during flood stages of the Missouri River" ...
and _spinifer_ occasionally ... "in the backwaters where stagnant
ponds had been formed." In southcentral Kansas, Burt (1935:321)
reported _muticus_ from "a sandbar at junction of a small creek and
Medicine River" ... and ... a "shallow sand-bottomed, algae-filled
pasture streamlet." The same author reported _spinifer_ from a
"sand-bottomed prairie streamlet" ... and ... "an alga-filled pool
near a stream." Burt (_loc. cit._) remarked that "No ecological
differences in general habitat and field behavior of _mutica_ and
_spinifer_ are evident in Kansas." Clarke (1958:21) observed
_spinifer_ in Long Creek (Osage County, Kansas), which is a winding
stream, characterized by numerous deep holes alternating with rocky
riffles, and having high and wooded banks, and mostly mud bottom but
occasional rock bottom.
Marr (1944:490) mentioned a _spinifer_ that was obtained on the bank
of a small, mud-bottomed stream in the Texas panhandle, and Linsdale
and Gressitt (1937:222) recorded _spinifer_ from irrigation canals in
Baja California.
In southern Florida, _ferox_ occurs in all fresh-water habitats
(Duellman and Schwartz, 1958:272). Carr (1940:107) reported _ferox_ as
widely distributed in streams, lakes, big springs and canals. Judging
from the numbers of turtles, "the larger canals in the Everglades must
represent something like an optimum habitat" (Carr, 1952:417). Wright
and Funkhouser (1915:119) wrote that in the Okefinokee Swamp, _ferox_
was especially abundant where the water is deep and the bottom soft,
and the species was found wherever there were alligators. Deckert
(1918:31) wrote that young _ferox_ were taken in springs and brooks
near Jacksonville, Florida. Marchand (_in_ Carr, 1952:417-19) observed
_ferox_ while water-goggling in Florida and noted that individuals
buried themselves in deep water in white sand, mud or bubbling
mud-sand springs, sometimes where there was vegetation overhead.
Neill (1951:16) collected _ferox_ in marshes, "prairies," flood-plain
lakes, lagoons, ox-bow lakes, mangrove swamps, rivers, creeks,
calcareous spring runs, man-made lakes and lime sinks. The same author
(_loc. cit._) reported taking _agassizi_ (= _asper_) in large muddy
rivers, clear "blackwater" streams, calcareous spring runs, creeks,
marshes, lagoons, ox-bow lakes, flood-plain lakes, lime sinks,
man-made lakes, and smaller ponds. Crenshaw and Hopkins (1955:16),
however, stated that in the area where _T. ferox_ and _T. spinifer
asper_ overlap, "_asper_ is nearly always an inhabitant of fluviatile
situations whereas _ferox_ is equally closely confined to
non-fluviatile lakes and ponds"; in the region of sympatry, Schwartz
(1956:8) reported _ferox_ from "a moderately fast, blackwater stream
[Combahee River, South Carolina]."
Carr (1952:417) wrote that _ferox_ is not uncommon near the mouths of
streams in brackish waters, where the tide must occasionally take it
to sea, and cited Conant, who told of an individual found at sea in
Bahaman waters; Carr (1940:25) listed _ferox_ as occasional in the
marine-littoral, mangrove swamps, as did Neill (1951:16). Neill
(1958:26-27) mentioned his observance of _ferox_ at the mouth of the
Pithlachascotee River, Pasco County, Florida, where the water is
sufficiently saline to favor the growth of oysters, and added that
commercial fishermen had told him that these turtles are sometimes
netted with loggerhead sea turtles (_Caretta_) in the Indian River.
Neill (_op. cit._:5-6) also noted the presence of _ferox_ on Meritt
Island, which supports an extensive saltwater herpetofauna, off the
coast of Brevard County, Florida. Löding (1922:47) recorded _spinifer_
from Fig Island, Mobile County, Alabama, which is probably a marine or
brackish water habitat. Cagle and Chaney (1950:386) obtained one
_spinifer_ in a brackish marsh of the Sabine Wildlife Refuge,
Louisiana; the poor trapping returns here (one _Trionyx_ and one
_Pseudemys_ in 408 trap-hours) suggest that fresh-water species are
not abundant in brackish habitats. Neill (1958:26-27) has summarized
the occurrence of soft-shelled turtles in marine and brackish
habitats.
My own observations indicate a variety of habitat preferences; the
term "relatively clear" refers to waters in which visibility extends
four to six inches below the surface at night using a head-light.
Individuals of _spinifer_ have been taken in large, deep rivers having
a moderate to swift current, relatively clear water, mostly sand and
clay bottoms, and emergent débris intermittent along the shoreline;
the banks may be steep and of mud having a sparse growth of herbs
(Black Warrior River, south of Tuscaloosa, Alabama), or of low
extensive, sandy bars and beaches (Escambia River, near Century,
Florida, Pl. 50, Fig. 1). A juvenile _spinifer_ was taken by hand
among rocks in quiet water behind a rocky shoal in the large,
deep-channeled Ocmulgee River (near Hawkinsville, Georgia). Several
individuals of _spinifer_ were seen in the Flint River (near
Bainbridge, Georgia), which had a swift current in a wide, deep
channel, sandy or sand-silt banks, few brush piles along shore and
many oölitic, submergent snags on an otherwise sandy bottom; the water
was exceedingly clear and permitted water-goggling (this habitat has
been obliterated by a dam on the Apalachicola River). A large female
_spinifer_ was taken on a set line from the bottom of one of several
deep holes (approximately seven feet) that were connected by shallow
areas or riffles (near headwaters of Escambia River--Escambia Creek,
Escambia County, Alabama). Two large females of _spinifer_ (one
escaped) were taken on a trotline set in a large, deep, isolated
barrow pit near the Escambia River (near Century, Florida); there was
no aquatic vegetation, the water was slightly turbid, and the
substrate was of a sand-silt or mud.
In Arkansas, _spinifer_ has been taken in large deep rivers having
relatively clear water, a moderate current, steep banks four to 15
feet high, and a substrate of mud with few rocks (one taken on
trotline, escaped; Black River, near Black Rock, Lawrence County). Two
_spinifer_ were taken (trotline and hoop-net) from a smaller
(approximately 50 feet wide) turbid river having a swift current,
débris along the shoreline, and mud-gravel banks (Petit Jean Creek,
Yell County). Several _spinifer_ and _muticus_ were taken from the
White River (Marion County) having a sand-gravel or bed rock bottom
and clear water; individuals were collected by hand in shallow water
(approximately 3-1/2 feet deep) as they lay on the bottom in the main
channel where the current was moderate to swift or in a quiet-water
side channel having submergent vegetation.
Lake Texoma, an impoundment on the Red River, having a fluctuating
water level with no permanent stand of aquatic vegetation, a mud-rock
or sand-silt bottom, and turbid water (Pl. 49, Fig. 1) is a suitable
habitat for _spinifer_ and _muticus_. _T. spinifer_ is found in large
rivers having relatively clear water, moderate currents, emergent logs
and débris, and mud or sand banks (Little River, McCurtain County,
Oklahoma, Pl. 48, Fig. 1), or small, shallow, turbid creeks having
sand-gravel channels of pools connected by riffle areas (Mayhew Creek,
Choctaw County, Oklahoma).
Three _spinifer_ were taken from the Llano River (near Llano, Texas)
in a period of low water level in hoop-nets set in a large quiet-water
pond about four feet deep and having patches of rushes encroaching
into the water from the shore. The river bed of sand, gravel and large
boulders consisted of narrower, swift-water channels, small pools and
riffles, and large ponds.
Individuals of _T. s. emoryi_ have been taken in large ponds having
little or no current, turbid, deep water, and clay or sand-gravel
banks (Río Purificación, Padilla, Tamaulipas). Two _emoryi_ were
collected from a large pond (Río Sabinas, near Sabinas, Coahuila),
which was connected to an adjoining one by riffle areas and had little
or no current, relatively clear, greenish water, clay or mud banks, a
sand-gravel bottom, and was flanked by brush and large cypress trees.
A few _emoryi_ were trapped in hoop-nets that were set in the Río
Mesquites, a stream in central Coahuila approximately 20 feet wide and
six feet deep, flanked by dense stands of _Phragmites_, and having a
moderate current, relatively clear, pea-green water and a mud-sand
substrate with some gravel; the stream enlarged in some places to form
quiet-water coves (Pl. 48, Fig. 2). One adult male _emoryi_ was taken
from a crystal-clear, dendritic, pond (El Mojarral, near Cuatro
Ciénegas, Coahuila), having shallow areas averaging about two feet but
several deep holes--in one of these at the west end of the pond the
water was being emitted under pressure from an underwater cavern and
"bubbling" at the surface; the vegetation consisted of scattered
patches of water-lilies and stonewort; the bottom was a soft mud-marl,
and in some places was carpeted with shells of small gastropods. This
habitat corresponds to that of the type locality of _T. ater_ (Pl. 49,
Fig. 2); see description in Webb and Legler (1960:26). The water of
the ponds is warm; at 8 p. m. on July 31, 1959, the temperature of the
water at the type locality of _ater_ was 29° C., and the air was 27°
C.
An immature female _spinifer_ was taken on a trotline in a swift,
clear, cold-water habitat having mud banks and an abundance of brush
piles (Little Tennessee River, Monroe County, Tennessee). _T.
spinifer_ occurs also in large ox-bow lakes having relatively clear
water, extensive mats of submerged vegetation, a soft mud bottom, and
several emergent stumps and fallen logs (Lake Concordia, Concordia
Parish, Louisiana); alligator grass and cypress trees encroached to
the shoreline.
Locality data of some individuals of _spinifer_, _hartwegi_, _asper_,
_pallidus_ and _emoryi_ that were examined indicated that turtles were
captured in ponds, bayous, sloughs, lakes, impoundments, rivers and
creeks, indicating habitation of essentially all permanent waters.
A juvenile of _hartwegi_ was seen by Mr. Wendell L. Minckley on a
gravel bar jutting into a small, shallow creek having a mud-gravel
bottom (Carnahan Creek, Pottawatomie County, Kansas); the impounding
of the Big Blue River by the Turtle Creek Dam will obliterate this
habitat. Mr. J. Knox Jones, Jr. reported seeing a large softshell in a
narrow, shallow, clear sandy creek in Holt County, Nebraska.
_T. s. emoryi_ occurs in large rivers having generally turbid waters,
a moderate to swift current and mud or sand bottoms such as the Río
Grande; this habitat corresponds to that of large rivers in the
western parts of the range of _T. s. pallidus_ (Red and Washita) and
_T. s. hartwegi_ (Canadian and Cimarron). These last-named rivers, in
periods of low water level, often have shallow, clear, flowing water
in parts of the river bed. _T. s. emoryi_ has also been taken from
small creeks having bottoms of rocks and large boulders (Black River
Village, Eddy County, New Mexico; field notes of Sydney Anderson and
Kenneth Shain, June 12-14, 1958).
I received a hatchling _T. s. guadalupensis_ that was obtained in a
clear, shallow-water stream (Hondo Creek, Bandera County, Texas, on
April 12, 1958). The larger streams and rivers known to be inhabited
by _guadalupensis_ are generally clear having greenish-tinted waters.
The geographic distribution of _guadalupensis_ indicates that that
subspecies occurs principally in those waters that drain the
limestone-mantled, Edward's Plateau off the Balcones Escarpment; the
headwaters are characterized by clear, calcareous streams having
occasional travertine deposits. It is probably this type of habitat to
which Agassiz's statement (1857:408) of "clear, bold and rocky
streams" refers.
There are a few specimens whose locality data indicate a tolerance of
brackish-water habitats. An adult male _spinifer_ was obtained at
Delacroix Island, St. Bernard Parish, Louisiana, a locality said to
have exceedingly brackish waters (Dr. George H. Bick, St. Mary's
College, Notre Dame, Indiana); this adult male (TU 16170) is unique in
having a mottled and blotched pattern. Another adult male (_spinifer_,
TU 16071) was obtained in shallow water in Lake Pontchartrain at the
mouth of Tchefuncta Creek; the salinity at the time of capture was
recorded as 1.7 (datum from Dr. Royal D. Suttkus, Tulane University),
indicating only slightly brackish water. Two _spinifer_ (USNM
100409-10) and one _muticus_ (USNM 100406) were taken at Berwick Bay,
near Morgan City, St. Mary's Parish, Louisiana; the waters at this
locality are probably brackish. The tolerance of brackish waters
doubtless facilitates the dispersal of these turtles along coastal
marshes and swamps, and into adjacent drainage systems. The greater
number of records in the literature pertaining to _ferox_ suggest that
this species may be more tolerant of brackish and marine waters than
are _spinifer_ or _muticus_.
In summary, _T. ferox_ occurs in all fresh-water habitats, but chiefly
in lentic habitats in the northern part of its range where it and _T. s.
asper_ are sympatric. _T. ferox_ possibly is more tolerant of brackish
and marine waters than are the subspecies of _spinifer_ and _muticus_.
The subspecies of _T. spinifer_ occur in all fresh-water habitats. In
the southern part of the geographic range, which overlaps that of _T.
ferox_, _T. s. asper_ occurs principally in running-water habitats. _T.
s. pallidus_ and _T. s. asper_ are tolerant of brackish-water habitats.
_T. s. guadalupensis_, known at present only from rivers and streams,
occurs principally in river systems that drain the Edward's Plateau of
southcentral Texas. _T. ater_ is confined to crystal-clear ponds in
central Coahuila.
The subspecies _muticus_ occurs in large rivers and streams throughout
its geographic range, but is known from lakes and impoundments
principally in the southern part of its range (the northernmost record
is from Reelfoot Lake, Obion County, Tennessee); there is only one
record of _muticus_ from a small, shallow, headwater creek (Reno County,
Kansas), and only one from a lentic habitat (Meredosia Bay, Illinois) in
the northern part of its range. _T. muticus calvatus_ is known at
present only from rivers and streams.
The seemingly greater restriction of _muticus_ to running-water habitats
suggests less vagility than in _spinifer_ (Netting, 1944:86).
Size and coloration are adaptations to habitat. Soft-shelled turtles of
large size are best adapted to mesic, essentially continuous swampy or
marshy habitats, whereas small size is an adaptation to less continuous,
semi-isolated habitats. A turtle of the maximum size attained by _ferox_
in the habitat of _emoryi_ would, in a general way, probably be more
conspicuous and exposed to its enemies, both in the aquatic environment
and during overland excursions; perhaps the kind and amount of food
would be insufficient. In any event, small size is correlated with the
more arid habitats of the southwest, and large size with mesic ones in
the southeast. _T. ferox_, the largest species, and the smallest
population of _T. spinifer_ (resembling _muticus_) both occur in the
southernmost part of the range of the genus. This situation does not
support the corollary of Bergmann's Rule, that pertains to some groups
of terrestrial reptiles, in which those subspecies occurring farther
north, or in cooler climates during their season of activity, tend to be
smaller.
Within the species _spinifer_, the _emoryi_ group of subspecies are
pallid having whitish dots on the carapace and lack extensive black
pigmentation; these features seem to confer protective coloration on the
inhabitants of arid, essentially sandy or muddy habitats having
sluggish, turbid waters, whereas the more contrasting patterns of the
_spinifer_ group of subspecies eastward seem more suited to existence in
clearer, swifter waters.
The occurrence of the two clines, _spinifer-hartwegi_ and
_pallidus-guadalupensis_, in the species _spinifer_ are notable in that
the former occurs mostly in one large continuous drainage system, that
of the Mississippi, and shows no sharp break in the one character
distinguishing the two subspecies whereas populations composing the
_pallidus-guadalupensis_ cline are separated into several river
drainages, and show a relatively sharp break in several characters at
the Brazos-Colorado river divide. This situation seemingly supports the
thesis that clines are maintained by some sort of parallel gradient in
ecological or geological conditions. It is notable that streams draining
the Edward's Plateau (inhabited by _guadalupensis_) differ in quantity
(more) and quality (especially CO_{3}^{--}, Ca^{++}, and Mg^{++} ions)
of their solutes, and probably pH (higher) from those farther east
(Hubbs, 1957:102). The gross difference in habitats mentioned above
(sandy, turbid, sluggish streams in the west _vs._ clear, swift streams
in the east) may affect the differentiation recognizable in the
_spinifer-hartwegi_ cline.
Daily and Seasonal Activity
_Diurnal Habits_
Softshells bask on débris in the water or on banks close to the water;
basking presumably raises the bodily temperature. In general in the
southeastern and southwestern United States, I have seen softshells
basking only rarely but once saw six at one time close together on logs
in Bowie Creek, Hattiesburg, Mississippi (species undetermined). Surface
(1908:122) saw _spinifer_ in rows on rocks or logs in tributaries of the
Ohio River. Duellman and Schwartz (1958:271-72) stated that _ferox_
basks on banks or beds of aquatic vegetation. Deckert (1918:31)
mentioned large _ferox_ "sunning in shallow water at edge of pond."
Minton (1944:447) wrote that _muticus_ and _spinifer_ sun on steep mud
banks (Wabash River). Cahn (1937:180) stated that _muticus_ (in
Illinois) basks on banks at the water's edge but seldom on logs, and
suggests that _muticus_ is less prone to leave the water than
_spinifer_. According to Carr (1952:438), _muticus_ never basks on
logs or rocks. In Ohio, Conant (1951:159) mentioned _spinifer_ as
occasionally basking upon a log or rock, or sometimes on steep clay
banks of streams. On banks, quick escape is facilitated by directing the
head toward the water, thus eliminating the time that it would take to
turn around on land (Conant, _loc. cit._; Newman, 1906:129). Evermann
and Clark (1920:593) mentioned _spinifer_ as basking on sandy or grassy
shores, and large boulders. Muller (1921:181) wrote that _muticus_ basks
four to ten feet from the water's edge on gently sloping sand and mud
shores of small islands in the Mississippi River (near Fairport, Iowa).
Muller stated that basking usually occurs in the morning, up until 2 p.
m., and that beaches with a northern exposure were preferred; he
observed 37 turtles within a 50-foot stretch of beach. In captivity,
hatchlings bask on wire-mesh supports.
I have frequently observed softshells floating at the surface of the
water, a habit previously mentioned by Surface (1908:122) and Pope
(1949:305, 311). Individuals of _Pseudemys_ and, to a lesser extent,
_Graptemys_ also float at the surface; those kinds of turtles and
softshells at least, often appear at the surface of the water, seemingly
as a result of an inquisitiveness, following repeated disturbances that
cause submergence.
Newman (1906:131) described the active pursuit of food: "They crawl or
swim along the bottom, thrusting their snouts under stones and into
masses of aquatic vegetation, occasionally snapping up a crayfish or
larva that they have succeeded in dislodging. They do not tear up their
food, but swallow it whole, using the forefeet to assist in forcing it
down." Surface (1908:123) suggested that softshells may feed "upon
insects which may be found floating on the water," and I have had
captives take insects from the surface of the water. Carr (1940:107)
also wrote that _ferox_ and numerous gars in the Tamiami Canal, often at
the mouths of the tributary ditches, snap at each other furiously as
floating bits of food are washed in from the Everglades. Another habit
that has been mentioned as an aid in acquiring food (Breckenridge,
1944:186; Conant, 1951:156; Hudson, 1942:101) is burrowing just below
the surface in a soft bottom in shallow water, to ambush passing fish,
or other food. Presumably all kinds of softshells do this in both
shallow and deep water of lakes or rivers having a suitable substrate;
_spinifer_ and _muticus_ have been reported to burrow in shallow waters
(no observations in deep water) by Agassiz (1857:333), Cahn (1937:180,
189), Conant (1951:159) and Weed (1923:48). Marchand (_in_ Carr,
1952:417-19) noted that _ferox_ burrows in deep water, and mentioned
that in areas of bare white sand a group of fish invariably surrounds
them, and one can locate buried softshells by observing these particular
schools of fish. No mention was made of the turtles attempting to catch
the fish. Other associations of soft-shelled turtles and fish have been
described. Kirtland (_in_ DeKay, 1842:7) observed several large bass
that closely followed large numbers of turtles floating at the surface.
Newman (1906:131) reported the observations of fishermen in Lake
Maxinkuckee that large-mouth black bass stay not far away from swimming
softshells; the same author also mentioned the observations of Jacob
Reighard, who suggested that bass may be feeding upon minnows that he
noticed following softshells. Seemingly some sort of commensalistic
relationship exists whereby fish acquire food that is dislodged by
grubbing and scurrying of softshells. Probably food is pursued on
occasion from a buried position, but this habit probably is not executed
specifically for obtaining food. Newman (_op. cit._:129) was of the
opinion that burrowing in shallow water is a habit to facilitate
"warming up."
Marchand (_loc. cit._) also wrote of other notable underwater
observations on _ferox_ in Florida. He commented on this turtle's
inquisitiveness in deep water and unconcern upon being touched or even
upon being handled to some degree. Calf-deep in soft mud, he noted a
turtle that "emerged from the mud of the bottom, headed up toward shore,
circled, and when about three feet above the bottom dived suddenly and
completely disappeared." Marchand wrote that some areas on the bottom
(Crystal Springs), which are rooted up by the burrowing of softshells,
are bare and soft, and assume a characteristic, easily recognized,
appearance.