In northeastern Kansas ornate box turtles are dormant from late
October to mid-April--approximately five and one half months of the
year. Individuals may be intermittently active for short periods at
the beginning and end of the season, however. Once a permanent
hibernaculum is selected dormancy continues until spring; unseasonably
warm weather between mid-November and March does not stimulate
temporary emergence. There is little movement during dormancy except
for the deepening or horizontal extension of the hibernaculum.
Woodbury and Hardy (1948:171) found desert tortoises (_Gopherus
agassizi_) in dormancy from mid-October to mid-April in southwestern
Utah; some tortoises became temporarily active on warm days in winter.
Cahn (1937:102) was able to compare hibernation in several individuals
each of _T. ornata_ and _T. carolina_, kept under the same conditions
in Illinois. Individuals of _T. ornata_ burrowed into the ground in
October, two weeks before those of _T. carolina_ did, and continued to
burrow to a maximum depth of 22A1/2 inches. Some individuals of _T.
carolina_ spent the entire winter in the mud bottom of a puddle and
became semiactive on warm winter days. Other individuals of _T.
carolina_ burrowed nearly as deeply as did _T. ornata_. Individuals of
_T. ornata_ emerged from hibernation one or two weeks later in the
spring than did those of _T. carolina_. There are some indications
that populations of _T. carolina_ in eastern Kansas are dormant for a
shorter period of time than those of _T. ornata_ but comparative
studies are needed to verify this. Richard B. Loomis gave me a large
female of _T. carolina_ that he found active beside a highway in
Johnson County, Kansas, on November 23, 1954; on that date most
individuals of _T. ornata_ under my observation had already begun
permanent hibernation but a few at the Reservation were still
semiactive.
Fitch (1956b:438) listed earliest and latest dates on which box
turtles were active at the Reservation in the years 1950 to 1954; in
the five year period box turtles were active an average of 162 days
per year (range, 140-187) or approximately 5.3 months of the year. It
is significant that 1954, having the most days of activity was,
according to my studies of growth-rings, an exceptionally good year
for growth. Fitch's data indicate the approximate season of growth and
reproduction but not of total activity, since he did not take into
account the sporadic movements of box turtles in late fall and early
spring.
Activity in autumn is characterized by movement into ravines and low
areas; many turtles move into wooded strips along the edges of fields
or small streams. Sites protected from wind, providing places for
basking and for burrowing, are sought. Burrows of other animals, along
the banks of ravines, were often used for temporary shelter;
overhanging sod at the lips of ravine-banks provided cover beneath
which turtles could easily burrow. After mid-October progressively
fewer box turtles were found in open places and activity was
restricted to a few hours in the warmest part of the day.
Low air temperature probably is the primary stimulus for hibernation.
Autumn rains are usually followed by a decrease in general activity.
Rain probably hastens burrowing by softening the ground.
Ornate box turtles more often than not excavate their own hibernacula.
Digging begins with the excavation of a shallow form which is deepened
or extended horizontally over a period of days or weeks. Such
hibernacula are sometimes begun at the edges of rocks or logs; the
overhanging edge of an unyielding object acts as a fulcrum on the
shell and hastens digging. Ornate box turtles are slow but efficient
burrowers.
Forms in open grassy areas are begun at an angle of 30 to 40 degrees;
an adult box turtle requires approximately one hour to burrow far
enough beneath the sod to conceal itself but can dig into soft, bare
earth much more rapidly. Once a hibernaculum is begun, all four feet
are used for its excavation, the front feet doing most of the digging
and the hind feet pushing loose earth to the rear.
Several turtles were seen entering burrows and dens in late autumn and
trailing records showed that some individuals visited several of these
shelters in the course of a single day.
By means of systematic probing of known hibernacula it was found that
they are deepened gradually in the course of the winter. Depth seems
to be governed by the temperature of the soil. Hibernacula in wooded
or sheltered areas were ordinarily shallower than hibernacula in open
grassland.
In the autumn of 1953-54 two pens were constructed at the Reservation
in order to study hibernation; one pen was on a wooded hillside and
the other was on open grassland. Turtles in the grassland pen were in
newly excavated hibernacula, just beneath the sod, on October 25 and
did not emerge for the remainder of the winter, whereas turtles in the
woodland pen were intermittently active until November 10.
Correspondingly, turtles in the grassland pen descended to depths of
eight and one half and 11A1/2 inches, respectively, whereas those in
the woodland pen were covered by a scant six inches of loose earth and
leaf litter. In 1954 four turtles were traced (by means of trailing
threads) to hibernacula on wooded slopes at the Reservation; two
entered permanent hibernacula on November 13 and two remained
semiactive until sometime after November 20. All four turtles spent
the winter in hibernacula that were not more than six inches deep.
Temperatures of the soil at a depth of nine inches were usually
slightly lower at the grassland pen than at the woodland pen on a
given date. It is probably significant that individuals with trailing
devices and individuals in experimental pens furnish the latest
records for autumn activity. The unnatural conditions created by
confining the turtles in pens restricted the number of hibernation
sites that were available to them; although trailing devices did not
affect the normal movements of box turtles on the surface of the
ground these devices certainly hampered the turtles somewhat in
digging. However, it is noteworthy that box turtles are able to move
about after mid-November, whether this is of general occurrence under
more natural conditions or not. Depths of hibernacula at the Damm Farm
were also influenced by amount of vegetation or other cover. Maximum
depth of hibernacula in more or less open situations ranged from seven
to 18 inches whereas a female hibernating in a ditch that was covered
with a thick mat of dead grasses was four inches beneath the surface
of the soil, and another female was only two and one half inches below
the floor of a den.
Several _T. ornata_ kept by William R. Brecheisen in a soil-filled
stock tank on his farm in the winter of 1955-56, burrowed to maximum
depths of seven to eight inches in the course of the winter. A layer
of straw covered the soil. All the turtles were alive the following
spring except for one juvenile, found frozen at a depth of one inch on
December 30 (the lowest air temperature up to this time was
approximately -12A deg.). Three adult and 24 juvenal _T. ornata_
hibernating in the earth of an outdoor cage at the University of
Kansas in the winter of 1955-56, were all dead on December 3 after air
temperatures had reached a low of -12 degrees.
Ornate box turtles are usually solitary when hibernating; in the rare
instances in which more than one turtle is found in the same
hibernaculum, the association has no social significance and is simply
a reflection of the availability and suitability of the hibernaculum.
The only communal hibernaculum--the "Tree Den"--at the Damm Farm was
discovered on October 16, 1955, after a turtle was traced to it by
means of a trailing thread. The flask-shaped cavity, approximately two
and one-half feet deep, in the north-facing bank of a narrow ravine,
had an entrance one foot wide and nine inches high, nearly flush with
the bottom of the ravine. Grasses on the bank of the ravine hung over
the entrance and nearly concealed it. The steep sides of the ravine
protected the entrance from wind.
Seven turtles were in the den when it was discovered, and on each of
five subsequent visits from October 20, 1955, to March 6, 1956, fewer
turtles were found in the den. Figure 24 shows the approximate length
of stay of each known occupant of the den. Only one of the turtles
(an adult female) that left the den returned. Turtles found in the den
on three visits in October were more or less torpid and were seen
easily from the entrance but on November 6 the two remaining
individuals had burrowed into the sides and floor of the den.
Three turtles (one female, one male, and one juvenile) were found in
separate form-hibernacula within a few inches of one another on
November 6, 1955 (Pl. 21, Fig. 2). The common entrance to all three
hibernacula was a shallow depression that resulted from an old
post-hole. Soil in the depression was loose and moist and ideal for
burrowing. The three hibernating turtles were situated, in a vertical
plane, at depths of 18 ([Male]), 12 (juvenile), and seven ([Female])
inches. One of the turtles hibernating at this place on November 6 was
basking on October 30 in the shelter of some tall weeds a few feet
from the hibernaculum.
[Illustration: FIG. 24. The approximate length of stay of each
known occupant of a den that was examined six times in the
winter of 1955-1956 at the Damm Farm. Most of the occupants
used the den as a temporary shelter and sought permanent
hibernacula elsewhere. One turtle left the den for
approximately two weeks and then returned to it for the rest
of the winter. The temperature of the air outside the den (A)
and the average body temperature of turtles in the den (B) are
given at the bottom of the diagram for each date the den was
examined. The symbol "J" represents a juvenal turtle.]
In general, body temperatures approximated the temperature of the soil
around the turtle. Body temperatures tended to be slightly higher than
soil temperatures in November and December but were slightly lower
than soil temperatures in the months of February and March. The lowest
body temperature recorded for any turtle that survived a winter was
2.7 degrees, taken from an adult female on December 26, 1955. Body
temperatures one to three degrees higher were common in the coldest
part of the winter. Turtles in shallow hibernacula, like those
observed in wooded areas at the Reservation, are probably subjected to
freezing temperatures at least for short periods but I have no records
of body temperatures this low, except where they were induced
experimentally. Turtles exposed to temperatures of zero degrees or
slightly lower would retain enough heat to survive without freezing
for a period of several hours or even a day if well insulated. A
temperature gradient exists within the body; cloacal temperatures, for
example, differ from temperatures deep in the colon and temperatures
in the dorsal and ventral parts of the body cavity (taken by
manipulating the bulb of the thermometer while it was in the colon)
differ from one another. Probably, therefore, some parts of some
turtles--probably the top of the shell or the extremities--freeze in
winter without causing the death of the turtle. Ewing (1939:91) found
a female of _T. carolina_, just emerging from hibernation, that had
lost some scutes from its carapace; he found the missing scutes in the
hibernaculum and attributed their loss to severe temperatures in the
winter of 1933-34.
The incidence of mortality due to freezing is unknown for most species
of reptiles. The observations of Bailey (1948) on DeKay snakes
(_Storeria dekayi_) and Legler and Fitch (1957) on collared lizards
suggest that rates of mortality are high in dormant reptiles. Bailey
(_op. cit._) suggested that winter mortality might act as a natural
check on snake populations. Neill (1948a:114) thought more box turtles
(_T. carolina_) were killed in Georgia by cold weather in late autumn
than "... by all other factors together," and that this winter
mortality acted as an effective check on population levels. Neill
reported that many turtles left their burrows in late autumn and began
to forage; if the temperature dropped suddenly, the turtles became
"... too torpid to dig" and froze.
If ornate box turtles are occasionally caught in the open by a sudden
cooling of air temperature, it would occur at a time of year when
temperatures would approximate freezing but would drop not far below
this level; laboratory and field records show that adults could
probably survive these low temperatures overnight and warm up
sufficiently on the following day to seek adequate shelter. Box
turtles deepening their burrows in winter do so at body temperatures
somewhat lower than 10 degrees (near the minimum temperature at which
co-ordinated activity was observed in the laboratory); turtles found
in the open in late October were known to burrow into the ground at
body temperatures of approximately 15 degrees.
Emergence from hibernation usually occurs in April but in some years a
few turtles may emerge as early as the first week of March. Emergence
is stimulated by temperature and humidity. Fitch (1956b:438) stated
that emergence was delayed until "... the ground has been sufficiently
moistened and until air temperatures have reached at least 26A deg.." Box
turtles at the Reservation emerged on April 21 in 1954 and from April
16 to 17 in 1955. William R. Brecheisen found recently emerged box
turtles in Anderson County on April 2, 1955, and March 6, 1956.
Turtles were found facing upward in their hibernacula in early March.
As the temperature of the soil rises, they move slowly upward, usually
following the route by which they entered. They remain just below the
surface of the soil for a week or two before actually emerging; this
final phase of emergence is probably hastened by spring rains that
soften the soil. Activity may be sporadic after emergence if the
weather is cold.
A number of box turtles at the Reservation emerged in a cold rain in
1954 when the temperatures of the air and ground were 16 and 13
degrees, respectively, but remained inactive for several days
afterward. In 1955 the air and ground temperatures were higher (28A deg.
and 17A deg., respectively) on the day of emergence and box turtles became
active almost immediately.