have brought out the fact that terrestrial poikilotherms, and especially
lizards, maintain fairly high and constant body temperatures through
behavioral thermoregulation, during their periods of activity. For
genera and species of lizards, there are optimum body temperatures,
which the individual tends to maintain, fluctuating within a range of
only a few degrees while it is active. Forms that are not closely
related may differ notably in their optimum temperatures, although
within any one genus the range is slight. For example in the iguanid
genus, _Sceloporus_, Bogert found that different species from such
distant regions as Arizona and Florida agreed in having body
temperatures approximating 35 deg. or 36 deg.C., while different members of the
teiid genus _Cnemidophorus_ in the same two regions were found to
approximate 41 deg.C. in mean temperatures. In commenting on the
distribution of North American lizards as affected by opportunity for
behavioral thermoregulation by direct insolation, Bogert (_op.
cit._:205) wrote: "Such secretive lizards as skinks (principally
_Eumeces_ in North America) with low body temperature preferences
approximating 30 deg.C. are dominant in Florida and the Gulf Coast, in
contrast to the Teiidae and Iguanidae (several genera in the United
States), which are far more abundant in the arid regions of the
Southwest." Bogert and Cowles (1947:19) record that in a large
individual of _Eumeces inexpectatus_ taken near the Archbold Biological
Station in Florida, the body temperature was 33.2 deg.C.
In the 1952 season, a small thermometer of the type described by Bogert
(_op. cit._:197) was frequently carried on collecting trips, and cloacal
temperatures were recorded for the lizards collected. For those found in
traps the opportunity for behavioral thermoregulation was limited, and
temperatures usually approximated those of the air. The circumstances of
capture, and the air temperatures were recorded for most of the skinks
taken. For those found under rocks or in other shelter, the temperature
usually approximated that of the immediate surroundings, and averaged
much lower than for those taken in the open, but some found in such
shelters had temperatures many degrees higher than their surroundings,
and were fully active, having evidently just taken to cover to escape
notice as the collector approached. As soon as a lizard was secured it
was held in a leather glove or heavy cloth to prevent conduction of heat
from the collector's hand, and a reading was taken within a few seconds.
Most of the skinks found in the open could not be caught immediately but
were secured only after minutes of maneuvering on the part of both
collector and lizard. In most instances this maneuvering probably
entailed some loss of heat by the lizard, as it interrupted its
thermoregulatory behavior to run to a place of concealment, usually in
shadow on a tree trunk, or in or beneath ground litter. Excluding all
those not found active in the open, the mean temperature, in a sample of
41, was 31.5 deg.C. +- .60. This figure is thought to be slightly too low
because of heat loss by many of the skinks in the time required to
capture them.
In order to test the range of tolerance and verify the preferred optimum
temperature of the five-lined skink, an experimental terrarium was set
up providing extremes of temperature at each end. A false floor of 1/8
inch wire screen was provided, with a seven-inch strip of galvanized
sheet metal beneath it at each end. Beneath the screen and sheet metal
at one end the space was filled with chopped ice, and "dry ice."
Observations were made on hot, clear summer days, with the terrarium
arranged so that the half of it containing ice, was in shadow, and the
other half was in sunshine. The strip of metal, warmed by direct
sunlight, became uncomfortably hot to the touch while at the other end
the sheet metal and overlying screen were cooled by the ice. A narrow
zone across the middle of the terrarium had screen but no underlying
sheet metal and was the only part within which the lizard could maintain
normal temperature, one end being uncomfortably hot and the other end
too cool. A large dead skink left on the metal strip in direct sunlight
for five minutes had a cloacal temperature of 45.3 deg.C., and after five
minutes on the screen at the cool end, its temperature had dropped to
25.5 deg.C. On several occasions a number of skinks were put in the
terrarium and their temperatures taken at brief intervals. Temperatures
ranged from 21.6 deg.C. to 37.7 deg.C. but were mostly within a much narrower
range, from 28 deg. to 36 deg.C. One skink that seemed to be sick was sluggish
in behavior, not responding to the extremes of temperatures as readily
as the other individuals and his temperature fluctuated widely and
irregularly. Eliminating this individual, 66 temperature readings taken,
from five other skinks, gave a mean of 32.6 deg.C. +- .235. While nearly all
the temperature readings were within a range of ten degrees, two of the
readings were outstandingly low and perhaps should be discarded. If this
is done, a mean of 33.8 deg.C. +- .19 is obtained for the remaining 64. There
is distinct bimodality in this series however, with a mean of 34.2 deg. for
the 49 higher readings, and a mean of 28.8 deg.C. for the 15 lower
temperatures. A similar bimodality is evident in the readings obtained
from skinks caught in the open under natural conditions. It seems that
the lower readings result from lags in the skinks' response when body
temperature drops slightly below the optimum. The skink is quick to make
adjustment whenever its temperature appreciably exceeds this optimum
level, and is in extreme discomfort at only a few degrees higher
temperature. At slightly lower temperatures, however, the skink
experiences no discomfort, and only slightly decreased efficiency in its
various functions, and its thermoregulatory behavior in making
readjustment toward the optimum is likely to be leisurely and
interrupted unless its temperature drops below 28 deg.C.
Catching the skinks in the experimental terrarium at frequent intervals
to take their temperatures involved some disturbance to them,
interrupting their thermoregulatory behavior. The experimenter's first
attempt to grasp a skink sometimes failed, and it then dashed about the
terrarium for several seconds, probably altering its temperature
somewhat. Nevertheless most of the lizards' movements were motivated by
thermoregulation. This was especially evident when they were left
undisturbed, and is illustrated by the following notes on behavior of an
adult female and half-grown young of _fasciatus_ and a young _E.
obsoletus_ on the afternoon of July 21, 1952.
2:58 All resting over cooled metal.
3:01 Female runs to line of sunshine and shadow, coming to rest with
approximately half her body in sunshine, the other half in shadow
over the cooled metal.
3:03 Female reverses position so that hindquarters previously in shadow
are now in sunshine, and forequarters are in shadow.
3:03-1/2 Young runs to middle coming to rest in sunshine on screen.
3:04 Female moves back to the cool end.
3:05 Young moves to edge of cooled metal but not over it, in a narrow
middle strip that has sunshine.
3:05-1/2 _E. obsoletus_ moves from cool end to middle, partly in
sunshine.
3:07 _E. obsoletus_ adjusts its position in narrow middle strip of shadow
just off the cold end.
3:08 Boards used for shading adjusted back slightly so that
_E. obsoletus_ is in sunshine.
3:08-1/2 _E. obsoletus_ moves back to cold end.
3:10 Young still at middle, but resting mainly over cooled metal with
tail partly in sunshine.
3:10-1/2 Young moves out into sunshine at middle.
3:11 Female moves out into sunshine at middle. _E. obsoletus_ moves over
cooled metal to its edge, coming to rest partly in sunshine.
3:12 Female moves back over cooled metal.
3:13-1/2 Air temperature 33.3 deg.C. _E. obsoletus_ shifts a short distance
so that it is resting entirely over the cooled metal, with only part
of its tail receiving sunshine.
3:17 Young moves about in sunshine, then comes to rest in shadow with half
its body over cooled metal.
3:19 Young shifts so that more than half its body is in sunlight in middle
section.
3:20 Young shifts away from sunlight, coming to rest with most of its body
over the cooled metal.
3:21-1/2 Female moves from cooled metal to sunshine in middle strip.
3:23 Female moves out of sunshine, partly over edge of cooled metal.
3:30 Young moves off cooled metal, coming to rest over edge of warmed metal
in narrow middle strip that is in shadow.
3:30-1/2 Young moves back away from warmed metal, pauses briefly, and then
moves over cooled metal coming to rest there.
3:31 Female shifts so that about half her body is in sunshine in the middle.
3:32 Female shifts back into shadow, partly over cooled metal.
3:33 Boards providing shade readjusted so that female is in sunshine.
3:33-1/2 Female moves back into shadow over cooled metal.
3:38 Female moves to edge of cooled metal, resting partly in sunshine;
sky is becoming slightly overcast.
3:40 Temperature of female 33.4 deg.C.
3:41 Temperature of young 32.8 deg.C.
3:43 Temperature of _E. obsoletus_ 32.4 deg.C.
3:45 Young moves to shaded edge of warmed metal. Finds a dead spider
dropped there and eats it.
3:47 Temperature of female 32.3 deg.C.
3:48 Temperature of young 36.4 deg.C.
3:50 Temperature of _E. obsoletus_ 33.8 deg.C.
3:52 Sky partly overcast with thin layer of clouds;
observations concluded.
Having once emerged from its hiding place a skink becomes more or less
independent of the temperature of the air and substrate, as it is
capable of thermoregulation through insolation. However, after a period
of cooling and inactivity in dormancy, or merely resting for the night
in temporary shelter, the skink is dependent on warmth from the air or
substrate or both to become sufficiently activated so that it can emerge
and take advantage of direct sunlight. About 10:00 a. m. on April 13,
1951, when the air temperature was a little less than 10 deg.C., a large
adult male rustling among dry leaves attracted my attention. Obviously
recently emerged from hibernation, he was caked with dried mud and his
eyelids were nearly sealed shut. He had been sunning, however, and was
active enough to elude my attempts to catch him, as he scurried into a
deep crevice under the ledge. On the morning of March 24, 1951, while
the temperature was still between 10 deg. and 15 deg.C., a subadult skink, the
first one of the season, was seen sunning itself at the entrance of a
deep crevice under the ledge. This skink was still not fully active, and
its movements were stiff, yet it was alert and wary, and it quickly
retreated back into the crevice. During the first week of May, 1952,
skinks were active in abundance and numbers were caught daily in funnel
traps and pitfalls. On May 9, however, the maximum air temperature was
16.5 deg.C. with cloudy sky and occasional showers. Under these conditions
skinks stayed under cover; none was seen in the open nor caught in a
trap, and several found under rocks were slow and sluggish. On May 10 a
terrarium with several adults was placed in dilute sunshine beside a
window in an unheated room. After a period of basking the skinks were
stimulated to activity, but were unable to attain normally high
temperatures, and as a result their movements were like slow motion
caricatures of the normal behavior. Males approached each other with
menacing demeanor, with heads turned, snouts depressed, and forequarters
standing high. Frequently one would edge up to another and bite hard at
its flanks. The several males were sexually aroused by the presence of
the two females, but were capable of only the preliminary phases of
courtship, in delayed and protracted form. The temperature of one was
18.2 deg.C. when the sun had nearly set and activity was tapering off, at an
air temperature of 16.2 deg.C. At 16 deg.C. skinks in a terrarium with no access
to sunshine for the most part showed no interest in food and kept out of
sight under cover. When exposed their activity was directed almost
entirely toward burrowing into the substrate or searching for objects
beneath which to hide. One adult female was partly exposed by scraping
away loose soil into which she had burrowed. A mealworm was then dropped
just in front of her head. She tested it several times with her tongue
and then ate it without emerging, her movements being much less brisk
than they normally are in feeding. Probably this approximates the
threshhold temperature for feeding behavior. At 19.5 deg.C. the several
skinks in this terrarium were moving about in the open although they
were not exposed to sunshine, and they accepted food avidly when it was
offered, but were much slower than at optimum temperatures. On May 16,
1951, when a pair of skinks were put together in a terrarium in the
laboratory at 21 deg.C., copulation ensued but it was of longer duration
than in other observed instances, seemingly because of the relatively
low temperature.
Relatively few temperature readings on gravid or brooding females under
natural conditions were obtained as they were easily disturbed and
tended to desert their nests at slight provocation. To avoid desertions
handling was kept to a minimum. Occasionally gravid females were caught
in the open, but most of them were in nest burrows under flat rocks.
These females found in nests were mostly cold to the touch, and the
temperature readings taken on some of them usually approximated the air
temperature, being either higher or lower (depending on whether the air
was cooling or warming and whether the lizards were warmed by contact
with rock or soil receiving sunshine). On May 23, 1952, 22 skinks were
seen, four adult males, seven adult gravid females, and 11 young. Of
these the adult females all were in nest burrows, and were cold and
slow; consequently all of them were caught without difficulty. The males
and young, however, were either fully warmed or warm enough to escape
rapidly, so that only three of the young and no adult males were caught.
Temperatures of the females tested were 25.6 deg., 23.6 deg., 23.5 deg., 22.3 deg., and
19.4 deg., and for the three young, 32.8 deg., 28.4 deg., and 28.4 deg.. Air temperature
varied from 20.5 deg. to 24.8 deg.. For the total of 30 females in nest burrows
whose temperatures were taken in 1952, the average was 26.3 deg.C, ranging
from 16 deg. to 34 deg.. Gravid females, and those with nests and eggs were
rarely seen in the open.
The five-lined skink is confined to a region where summer rains are
frequent. It is evident that a regular supply of drinking water is one
of the most critical ecological requirements. Bogert and Cowles
(1947:19) found that an _E. inexpectatus_ experimentally kept at high
temperature lost moisture at a more rapid rate than any other reptile
tested (including two other kinds of lizards, four kinds of turtles, an
alligator, and three kinds of snakes). They remarked that this rapid
moisture loss presumably accounts for the inability of skinks to survive
in containers when no moisture is readily available, and also accounts
for their absence in truly arid habitats. The Natural History
Reservation is situated near the western edge of the species' range in a
climate that may be near the limit of its range of tolerance. However,
on most summer mornings low woodland vegetation is copiously laden with
dew, and this evidently fulfills the need for drinking water. Diminution
of surface activity and retirement to underground retreats seem to be
closely correlated with cessation of rains in late summer. After
rainless periods in August and September, when morning dew is no longer
available these skinks, especially the adults, are no longer regularly
seen in the open. They have retreated to underground shelters where they
spend nearly all their time. The time of disappearance varies from year
to year and the correlation with varying weather conditions seems
obvious. While no actual experiments were performed to determine the
moisture requirements, it is evident that the need for moisture rises
sharply with increased temperature. Skinks that are dormant in
hibernation survive for periods of months without drinking, with but
little loss of weight. In their underground shelters temperature is low
and presumably relative humidity is high. At temperatures above their
optimum of approximately 34 deg.C. the skinks are especially subject to
rapid moisture loss, since evaporation of body moisture is resorted to
as a device to keep the temperature below the lethal level. The skinks
subjected to extremes of temperature in an experimental terrarium were
seen to lap up condensed moisture on the cooled metal plate at intervals
of a few minutes. After an hour or more in the experimental terrarium
they seemed somewhat debilitated. Skinks brought from the study areas to
the laboratory for weighing and other records, were ordinarily returned
on the following day. When circumstances prevented adherence to this
schedule in hot summer weather, mortality could be expected in the
skinks kept in cloth bags or glass containers, unless water was
provided. Dramatic weight loss of up to more than 30 per cent was
recorded in some individuals, kept at the high temperatures which
usually prevailed in the laboratory, over periods of days in the summer.
Skinks having access to drinking water often ingest amounts far beyond
their immediate requirements, which may be stored in the bladder and
drawn upon over periods of days as it is needed, or may be utilized to
dampen the soil of the underground shelter and raise the humidity, as
incubating females seem to do.
GEOGRAPHIC RANGE AND THE DECIDUOUS FOREST HABITAT
EUMECES FASCIATUS corresponds in its distribution with the original
hardwood forests of eastern North America, as mapped by Braun
(1950:cover folder) and the "Oak-Wild Turkey Biome" of Shelford
(1945:240). Few species of vertebrate animals have ranges that coincide
more closely with this extensive area (exclusive of the northern edge,
that part characterized by Braun as the Hemlock-White Pine-Northern
Hardwoods). This latter is a mixed forest which actually is transitional
between the more typical deciduous forest farther south and the Taiga
Biome (or Formation) to the north, which is dominated entirely by
conifers. At the northern edge of its range _Eumeces fasciatus_ is much
less generally distributed than it is farther south. Although it is well
established and even may be locally numerous in South Dakota, Minnesota,
Wisconsin, northern Michigan, Ontario, northern New York, and
Connecticut, the locality records from these states are few, and
seemingly represent isolated and widely separated colonies that are able
to persist because of favorable combinations of environmental factors
not of general occurrence in the surrounding regions. Figure 6 shows the
extent of the hardwood forests as mapped by Braun (excluding the
transitional Hemlock-White Pine-Northern Hardwoods Association) with
specific locality records of _E. fasciatus_ included in all outlying
portions of the range. The locality records are those published by
Taylor (1936:206-212) supplemented by other marginal records, more
recently published, by Hamilton (1947:64) for New York, Breckenridge
(1944:97) for Minnesota, Hudson (1942:42) for Nebraska, Smith (1950:185)
for Kansas, Brown (1950:116) for Texas, Neill (1948:156) for Georgia,
and Neill and Allen (1950:156) for Florida. Along the northern edge of
its range, the skink invades the Hemlock-White Pine-Northern Hardwoods
Association, in Massachusetts, New York, Pennsylvania, Ontario,
Michigan, and Wisconsin, but does not penetrate far into it anywhere.
Correspondence of its northern limits with those of the Oak-Chestnut,
Maple-Basswood, Beech-Maple and Oak-Hickory associations is remarkably
close, considering the fact that the boundaries of these climax
associations are not sharply defined; rather they merge by gradual
stages into the northern coniferous forests, with outlying peninsulas
and islands where conditions are favorable.
The outlying northern localities where _E. fasciatus_ occurs within the
Hemlock-White Pine-Northern Hardwoods Association are all within the
region of Pleistocene glaciation, which 20,000 years ago, or even more
recently, were covered with the continental ice mass during Wisconsinan
time. Yet the localized northern populations of skinks evidently are
relicts from a time when favorable conditions were more widespread in
the general region. Braun (_op. cit._:464-465) indicates five successive
postglacial stages in the trends of climate up to the present, as
revealed by bog pollen profiles: (1) Cool and moist; (2) warm and dry;
(3) warm and humid; (4) warm and dry; (5) cool and moist. Stages 2 and 4
would have been most favorable for encroachment of the skink into
glaciated regions, whereas stages 3 and 5 might have caused retrenchment
of its populations. In view of the localized habits of individuals, and
the lack of any mechanism for rapid dispersal, the time available seems
no more than adequate for the distance of 200 miles or more northward
that the skinks must have moved since the final retreat of the ice
sheet. This northward movement involved crossing of formidable barriers
such as the Great Lakes. Even minor barriers such us small rivers and
creeks, might be expected to halt population movements for long periods.
[Illustration: FIG. 6. Geographic distribution of _Eumeces fasciatus_ as
indicated by published records (marginal and near-marginal records
shown, excluding those of doubtful validity). (1) Distribution of the
Deciduous Forest Formation of eastern North America, as mapped by Braun
(1950), but excluding the Hemlock-White Pine-Northern Hardwoods
Association that is transitional to the more northern coniferous
forests. (2) The shaded area in Kansas that is outside the Deciduous
Forest Formation comprises the Kaw River District, Cherokee Prairie
District, and southern Osage Savannah Biotic District (Cockrum, 1952).]
The over-all geographic range is approximately square, roughly a
thousand miles across, from north to south and from east to west. On the
east and south it is limited by the Atlantic Ocean and the Gulf of
Mexico. On the north and west its limits correspond with those of the
hardwood forests. On the northwest, it reaches southwestern Minnesota
and the southeastern corner of South Dakota, extending far out into
peninsular extensions of the Oak-Hickory Association which penetrate
westward into the prairies along the main river valleys.
In Kansas it occurs over the eastern one-fourth, west to the Flint
Hills, and a little farther west in peninsular extensions of the forest
along some of the main river valleys. In Braun's map the Deciduous
Forest Biome is shown to reach only the eastern edge of Kansas along the
Kaw River and Missouri River at and near their junction, the Osage (or
Marais des Cygnes) River valley near the Missouri border, and the
southeastern corner of Kansas. However, for almost 100 miles farther
west from the Missouri border, the country has the aspect of a savannah
with scattered groves of trees on hillsides and along streams, providing
suitable habitat. The distribution of the five-lined skink in eastern
Kansas corresponds well with certain "Biotic Districts" as mapped by
Cockrum (1952:12), namely the Kaw River, Osage Savannah (southern part),
and Cherokee Prairie. Conversely the skink is excluded from the Short
Grass Plains and Mixed Grass Plains Biotic Districts which occupy nearly
all of the western three-fourths of the state. There are two specimens
in the University of Kansas Natural History Museum, labelled Ranson,
Ness County. This locality, in the western third of the state, more than
150 miles from any other recorded station, may represent an isolated
colony; however Smith (1950:185) states that the record needs
verification, and it is not included in the map, Figure 6.