The thermal biology of the Turks and Caicos Islands rock iguana Cyclura carinata


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The thermal biology of the Turks and Caicos Islands rock iguana Cyclura carinata
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xvi, 367 leaves : ill. ; 28 cm.
Auth, David L
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Iguanas   ( lcsh )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )


Thesis--University of Florida.
Includes bibliographical references (leaves 347-366).
Statement of Responsibility:
by David Leslie Auth.
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University of Florida
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All applicable rights reserved by the source institution and holding location.
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I am grateful to numerous members of the faculty of the University

of Florida: to Walter Auffenberg, Lewis Berner, Robert DeWitt, Thomas

Emmel, and Howard Wallace, for their faith in my competence as a zoolo-

gist; to Archie Carr, John Kaufmann, Brian 'rNab, and Hugh Popenoe, for

their forebearance, patience, and time as members of the Ph.D. committee;

to John Anderson, John Brookbank, William E. S. Carr, Thomas Hollinger,

David Johnston, James Nation, Michael O'Rand, and Ronald Wolff, for the

pleasure of being a laboratory teaching assistant for their courses; to

Gerald Olsen, for introducing me to the anesthetic halothane; to Robert

DeWitt, John Ewel, Brian McNab, and Horst Schwassmann, for use of equip-

ment; and to James Heath, whose work and brief personal contact started

my interest in lizard thermcregulation.

I thank the New York Zoological Society for the financial support

necessary to accomplish the research. The University of Florida has

provided extensive support throughout my graduate career, in the form cf

teaching assistantships in the Zoology Department and the College of

Veterinary Medicine. Educational assistance through the G.I. Bill and

the Naval Reserve proved essential.

John Iverson introduced me to the habitats and habits of Cyclura

carcinata and continued to aid me in many ways during the study. Diderot

Gicca, Dagmar o. rner, and Thomas Wiewandt willingly shared their knowl-

edge of other species of Cyclura.

C. W. (Liam) Maguire and Bill and Ginny Cowles of the Meridian

Club, Pine Cay, permitted me to stay for practically nothing in the lap

of luxury while working in the field. They were most hospitable hosts.

Gaston Decker, Chuck and Cathy Hesse, and Francoise de Rouvray, also of

Pine Cay, helped me in many ways.

Alan Bolten, Jon Baskin, and William Link were superior companions

and considerate office mates. Alexis Arends, Susan Barnard, Hugh Ellis,

Michael May, Ken Prestwich, and Perran Ross gave needed technical

assistance. Karen Bjorndal, David Deitz, Dale Jackson, Howard Kochman,

Anne and Peter Meylan, and Michael Marshall all provided moral support.

I owe the greatest debt to my mother, Mildred G. Auth, my father,

Eugene F. Auth, and my brothers, Ronald and Dennis.



LIST OF TABLES . . .. . vii


ABSTRACT..................... ........ xiv

INTRODUCTION. . . . .. 1



Climate of Water Cay . . ... .. 24
Diel Body Temperature Cycle of a Heliothermic Lizard .... 31
Regulating Phase Body Temperature in the Field ... 34
Temporary Hyperthermia and Hypothermia . ... 44
The Relationship of Pertinent Environmental Variables
to Regulating Phase Body Temperatures . .. 55

Season . . ... 55
Habitat Complexity . . ... 62
Cloud Cover. . . ... 67
Shaded Air Temperature . .. 73
Substrate Temperature. .... .. . 75

Patterns of Heat Transfer between Penned Iguanas and
their Environment: The Three-Transmitter Study. ... 78
Statistical Analyses of Regulating Phase Body Temperature. 89

Body Temperature Maxima and Minima . .. 89
Skewness of Body Temperature Frequency Distribution. .. 107
Standard Deviation of Mean Body Temperature. .. .112

Rates of Lizard Heating and Cooling in the Field .119

Morning Heating and Regulating Phase .. 119
Lizard Cooling in Burrows. . .. 125


Lizard Activity. . . .. 132

Burrow Movement. . .... .132
Control of Lizard Emergence and Submergence. ..... .132

Morning Heating Phase. . .. 146
Regulating Phase . . ... 149
Foray Movement and Body Temperature. . ... 154
Feeding, Transmitter Passage Time, and Defecation ... 166
Drinking . . . 168
Nasal Salt Gland Secretion . .. 170
Time-Motion Study of Penned Lizards. . ... 171

Behavioral Thermoregulation. . ... 174

Description of Thermoregulatory Movements and Postures 174
Shuttling Behavior . . .. 184
Sun Orientation. . . 187
Thigmothermia. . . .. 200
Low Body Temperature Behavior. . ... 213
High Body Temperature Behavior . .. 216
Head-Body Temperature Differences. . ... 224
The Integument: Metachromatism and Reflectivity. .. .. 227
The Integument: Sensory Spots. . ... 231


Heating and Cooling Rates. . . .. 236
Aerobic Metabolism . . 248
Heart Rate . . . 253
Recovery from Maximum Exercise . .. 259

DISCUSSION. . . . .. 270

Body Temperature Relations . . .. 270

Comparison of Cyclura carinata's Mean Body
Temperature with Other Diurnal Lizards. ... 270
Seasonal Variation in Body Temperatures of
Active Lizards. . . .. 276
Stability of the Mean Preferred Body Temperature 277
Late Afternoon Maximum Body Temperature. ... 279
Thermal Safety Margins . .. 281
Panting Threshold. . . .. 282
Body Temperature and Reproductive State. . 284

Ethological Considerations . . .. 285

Lizard Activity. . . .. 285
Eurythermy vs. Stenothermy . .. 288
Comparative Thermoregulatory Behavior of
Heliothermic Lizards .... . .296
Complexity of Social Behavior in Cyclura carinata
as a Function of Latitude . .. 305
Nocturnal Lizard Aggregations. . ... 306

Physiological Considerations . .. 307

Aerobic vs. Anaerobic Metabolism . .. 307
Neural Basis for Shuttling Behavior in Lizards .... .312


LITERATURE CITED. ......................... .347

BIOGRAPHICAL SKETCH ......................... 367



1 Daily variation in relative humidity. . ... 30

2 Summary of regulating phase body temperatures of
lizards in the field. . . 35

3 Hyperthermia in CycZura carinata in the field ...... 47

4 A seasonal comparison of some environmental variables
at Site II on Water Cay . ... 56

5 Seasonal changes in regulating phase body temperature
in the field and in the laboratory thermal gradient 57

6 Vegetational cover at Sites I and II on Water Cay 66

7 Body temperatures of C.r:lra carinata confined to
cages with two structurally different habitats. ... 68

8 Skewness of frequency distributions of minimum and
maximum body temperatures . .. 91

9 Means and standard deviations of minimum and maximum
body temperatures of individual lizards and correlation
of maximum vs. minimum and minimum vs. maximum T b pairs 92

10 Linear regression analysis of daily minimum vs.
maximum Tb's and mean of daily Tb minima vs. mean of
daily Tb maxima for individual lizards. . ... 101

11 Skewness and kurtosis of Tb frequency distributions 118

12 Rates of lizard heating and cooling in the field during
the morning heating and regulating phases ... 120

13 Lizard cooling in burrows in the field. . ... 124

14 Lizard body temperature at emergence in the field ..... 131

15 Emergence and submergence times, temperatures, and
light intensities for free-ranging lizards in the
field . . ... . 146

16 Possible acclimatization of lizard activity .. 165

17 Effect of body temperature on the feeding rate and meal
size of penned Cyclura carinata . ... 167

18 Time-motion study of Cyclura carinata in the Gainesville
pen . . . 172

19 Skin patch heating . .. .. 198

20 Estimated thermal conductance during heating and cooling
of lizards in still air . ... 240

21 Correlations of lizard behaviors with body temperature
during heating and cooling in the cage and on the jig 245

22 Recovery oxygen for CyeOura carinata after seven minutes
of maximum exercise . .... .265

23 Comparison of actual mean recovery time after maximum
exercise with recovery times at three hypothetical rates
of oxygen utilization . .... 267

24 Field body temperatures of diurnally active lizards 271




1 Black body temperatures in the field. . ... 25

2 Air temperature in the shade at Gainesville, Florida
and Grand Turk, British West Indies . ... 26

3 Mean maximum wind speed at Site II in July. ... 28

4 Monthly precipitation on Grand Turk, British West Indies. 29

5 Body temperature record of Lizard 2 on February 10, 1976. 32

6 Summary of field body temperatures during the regulating
phase . . ... . 45

7 Lizard hyperthermia and hypothermia during the regulating
phase . . . 46

8 Patterns of regulating phase body temperature and distance
traveled in Cyclura carinata in a laboratory thermal
gradient. . . ... ..... 51

9 Hypothermia in a free-ranging lizard. . 54

10 Seasonal change in Cyclura regulating phase body
temperature in the Caicos and Gainesville, Florida. ... 59

11 Relationship of mean body temperatures in the field and
the thermal gradient for active lizards from several
families. . . .. 61

12 Influence of habitat on body temperature. ... 65

13 Effect of cloud cover on mean regulating phase body
temperature . . ... ..... 69

14 Effect of overcast duration on lizard body temperature
change . . ... ... 72

15 Correlation of lizard body temperature during the
regulating phase with shaded air temperature. ... 74

16 Thermoregulatory flexibility. . ... 77

17 Three transmitter record of a large male Cyclura
carinata in the Gainesville pen on August 21, 1975. ... .80

18 Partitioning of heat transfer in active penned
Cyclura carinata. . . .... .84

19 Rate of core body temperature change during the four heat
transfer conditions . .... .86

20 Correlations of the sum of daily heat transfer conditions
with lizard activity and mean body temperature. 88

21 Time distributions of four combinations of maximum and
minimum body temperature. . ... 97

22 Correlations of maximum vs. minimum Tb and the mean of
Tb maxima vs. minima for individual lizards ... 100

23 Hourly change in minimum and maximum body temperatures. .. 104

24 Timing shift of daily minimum and maximum Tb's. 106

25 Skewness of daily Tb frequency distributions. ... 110

26 Comparison of the level and precision of thermoregulation
of Cyctura carinata and Dipsosaurus dorsalis in continuous
thermal gradients . . ... .. 111

27 Correlation of the standard deviationofmean daily Tb
with mean daily Tb. . ... .. 113

28 Effect of body weight and mean Tb on the standard
deviation of mean Tb. . . ... 116

29 Hourly change in the mean and standard deviation of lizard
body temperature and shaded air and sand temperatures 118

30 Correlation of mean rates of heating and cooling in the
field with lizard body weight . .... 124

31 Correlations of parameters describing regulating phase
body temperatures . . 126

32 Lizard movements in a burrow. . ... 134

33 Seasonal change in lizard emergence and submergence times 136

34 Correlations of times of emergence and submergence with
body weight in penned Gainesville lizards ... .140

35 Gradual reentrainment of lizard emergence time after
release . . . 145

36 Lizard activity during the morning heating phase. ... .148

37 Daily and seasonal variation in activity. ... 151

38 Variable inhibitory effectiveness of cloud cover on
lizard activity . . 155

39 Influence of cloud cover on the length of lizard forays
and the mean rate of travel during forays ... 159

40 Correlations of foray length and rate of travel with mean
body temperature. . . .. ... 161

41 Body temperatures during forays ........... 163

42 Defecation body temperatures and timing . 169

43 Correlation of lizard mobility with confinement area. .. 173

44 Thermoregulatory motions and postures of Cyclura carinata 175

45 Lizard shuttling in the summer field cages. ... 185

46 Midday depression of shade seeking body temperature 188

47 Lizard orientation to a heat lamp during heating and
cooling in the photothigmotron. . ... 189

48 Positive and negative orientation during lizard heating
and cooling . .. 192

49 Daily and seasonal variation in sun orientation in the
Gainesville pen . .... ..... 195

50 Left vs. right side sun orientation in the Gainesville
pen . . . 196

51 Daily change in the pattern of travel during forays 199

52 Participation of the lizard's head, neck, and legs in the
reduction of substrate contact. . ... 203

53 Relative importance of lateral compression of the trunk
vs. head, neck, and trunk elevation . ... 205

54 Conductive and convective heating and cooling of a single
Cyclura carinata ........ .............. 206

55 Conductive heating and cooling of a single Cyclura
carinata, with and without simultaneous radiative
heating with a heat lamp. . ... 209

56 Thigmothermic responses of a single Cyclura carinata to
periods of increasing, stable, and decreasing substrate
temperature . . . 212

57 Behavioral responses of CycZura carinata at low body
temperatures .... . . .. 214

58 Daily adjustment of the panting setpoint to changing
heat input. . . ... ..... 220

59 Correlation of total panting time with head and gut
thermal lag times . . ... ... .222

60 Head-body temperature differences during heating and
cooling of a 1790 g male Cyclura carinata in the
Gainesville rooftop arena . ... 226

61 Integumental and substrate reflectivities ... 228

62 Density of sensory spots on different parts of the lizard
body surface. . . ... ..... 234

63 Heating and cooling rates of a 1435 g male Cyclura
carinata in a constant temperature chamber. ... 239

64 Breathing rates of lizards during heating and cooling in
a constant temperature chamber. . ... 247

65 Correlation of resting and maximum oxygen consumption
with body temperature ; . ... 250

66 Analyses of aerobic metabolism. . ... 252

67 Heart rate as a function of body temperature. .. .254

68 Heart rate analyses . .... .256

69 Relationship of oxygen consumption to heart rate at
different body temperatures . ... 257

70 Temporal pattern of body movements while struggling to
escape. . . ... .... .260

71 Effect of body temperature on the rate of recovery from
seven minutes of maximum activity . ... 263

72 Early and late phase recovery from maximum exercise in
Cyclura carinata at different body temperatures .. .269

73 Summary of body temperatures of selected behaviors and
physiological maxima of Cyclura carinata. ... 293


74 Effect of increasing body temperature on frequency
distribution skew and standard deviation of the mean
for minimum and maximum body temperatures ... 319

75 Hypothetical neural basis for changes observed during
increasing mean body temperature in Cyclura carinata. 324


Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy



David Leslie Auth

June, 1980

Chairman: Walter Auffenberg
Major Department: Zoology

The ecological, ethological, and physiological thermal biology of

Cyclura carinata, a large, tropical, herbivorous iguanine lizard, was

investigated on Water Cay in the Caicos Islands and in Gainesville,

Florida. The study lasted from June, 1974, until September, 1976, and

included four field trips totaling twenty weeks.

Far-field transmitters were placed in the coelom or gut of free-

ranging adult iguanas (675-1864 g) for long-term monitoring of core

body temperature (Tb) in the field. Mean regulating phase Tb ranged

from 38.0 to 39.7 C (February-October), quite high compared with most

other iguanids. Stenothermia was pronounced, with a mean, regulating

phase Tb range of only 3.3 C. Maximum voluntary Tb, 43.8 C, was only

2.4 C below the CTMax. The CTMin, 12.8 C, almost equalled the lowest

recorded environmental temperature.

Iguanas were initially hyperthermic in both the field and a

thermal gradient, the former the possible result of bacterial infection

or a transmitter meal and the latter of thermoregulatory learning.


Individual differences in regulating phase Tb were partially due

to variable vegetational cover and, perhaps, egg development in females.

Mean operant T 's did not correlate perfectly with seasonal change in

the ambient thermal environment. Mean regulating phase field Tb

exceeded mean preferred Tb. The latter did not change with Gainesville

seasonal acclimatization, whereas winter variance of mean Tb was less

than summer variance in both field and thermal gradient.

Mean regulating phase Tb was inversely correlated with cloud cover

time, the correlation improving with seasonal cooling. Tb was nearly

independent of shaded air temperature.

Heat transfer through the dorsal and ventral body was examined

using three transmitter placements on penned iguanas. Heat was usually

gained dorsally and lost ventrally; iguanas were thigmothermic only 20.7

percent of their active period, usually in combination with heliothermia.

Individual frequency distributions of regulating phase maximum and

minimum Tb's were commonly skewed positively and negatively, respectively,

whereas inclusive individual distributions were usually negatively

skewed. Standard deviations were slightly but not significantly greater

for mean minimum than mean maximum T 's. Change in Tb between any two

consecutive maxima was positively correlated with change in two

consecutive minima, with the first minimum immediately before or after

the first maximum. Individual mean maximum and minimum T 's were

directly and linearly correlated, the regression line extrapolating

to approximately the maximum voluntary tolerance. These results are

discussed in terms of dual-limit thermoregulation.

Iguanas were diurnally active all year and rarely escaped into

burrows due to overheating. Mean regulating phase heating was 1.15


times faster than cooling and 3.0 times slower than heating during

morning basking. Iguanas also heated faster than they cooled in a

constant temperature chamber, both when restrained and when permitted

to move about. Maximum Tb commonly occurred during late afternoon

basking. This and other results indicate that surface rather than

core body temperature is regulated.

Both length and rate of travel were independent of mean Tb between

35.0 and 40.5 C. Arboreal climbing, burrow excavation, defecation,

drinking, feeding, nasal salt gland secretion, and panting were also

examined in relation to mean Tb.

Thermoregulatory behaviors and postures were described. A

photothigmotron was constructed to quantify iguana light shadow and

substrate contact in a controlled thermal environment. Shuttling and

sun orientation were examined. A time-motion study revealed the low

activity rate of penned iguanas and activity partitioning between

foraging, social, and thermoregulatory behaviors. Thermoregulatory

behavior was quite similar to other heliothermic iguanids.

Resting and maximum oxygen consumption,and heart rate and

oxygen consumption during recovery from maximum exercise were determined

at different Tb's. Iguanas fatigued rapidly during maximum exercise,

yet rarely developed large oxygen debts in the field. Heart rate

increment, initial rate of recovery, and oxygen scope were greater

in the preferred Tb range.


Although much is known regarding the thermal biology of small

lizard species (see Heatwole 1976 for a review), large lizard species,

because of their rarity in numbers and usual distribution in isolated

areas, have received lesser attention. This is unfortunate, for large

mass confers certain advantages and disadvantages due to low heating

and cooling rates. This study investigates the thermal biology of a

species of rock iguana in the genus Cyclura Harlan, one of nine genera

in the subfamily Iguaninae (Avery and Tanner 1971). Although the genus

includes some of the largest lizards in the world, Cyclura carinata is

one of the smaller members (maximum weight of 1,864 g for males,

1,135 g for females).

Preliminary observations by Auffenberg (personal communication) in

1973 indicated that Cyclura carinata probably had a fairly high diurnal

operant or eccritic body temperature (T). This, coupled with large size and

a herbivorous diet, uncommon in lizards, suggested that its thermal biology

could in some ways be unique. A great deal of thermally related data had

already been collected for the desert iguana, Dipsosaurus dorsalis,a small

herbivorous lizard of the North American Southwest with a very high

preferred Tb (Porter et al. 1973). Thermally related comparisons of

Cyclura carinata with this species as well as with the larger iguanines,

Amblyrhynchus cristatus (White 1973), Iguana iguana (McGinnis and Brown

1966), and Sauromalus obesus (Johnson 1965) seemed worthwhile.

Continuous monitoring of the Tb of free-ranging lizards in the

field using radio-telemetry forms the basis for the present study. This


approach has only rarely been followed for large lizards (Stebbins and

Barwick 1968, McNab and Auffenberg 1976).

The natural history of CycZura carinata was examined simultaneously

from four directions by Dr. Auffenberg (feeding strategy), John Iverson

(autecology and ethology) and myself, under a grant from the New York

Zoological Society. The field site was located primarily on Pine and

Water Cays, on the northwest side of the Caicos Island Bank. Since the

goal of this research was to gain as much information as possible which

could be useful in guaranteeing the species' future survival, I chose to

attack the problem of thermal biology broadly, rather than emphasizing

any one aspect such as thermoregulation. Ecological, ethological, and

physiological approaches were taken, working only at the organismic

level and using free-ranging field, controlled field, and laboratory

studies. This synthetic approach has been utilized rather successfully

by Grenot (1976) for Uromatix acanthinurus, another fairly large

herbivorous lizard.

The field ecological approach to Cyclura carinata's thermal

biology depends on a thorough understanding of the thermal environment

in which the lizard lives. This means that cloud cover, wind speed,

black body temperature, shaded air temperature, and substrate tempera-

ture have to be monitored daily and seasonally as well as the lizard's

body temperature and its thermally related behavior. Then, environ-

mentally related questions can be answered. How does the lizard

respond to the rather constant easterly winds? Are these xeric habitat

animals able to stay out of their burrows even during the hottest part

of the summer day or are they forced underground, as is the smaller

Dipsosaurus dorsatis (Porter et al. 1973)? Is Tb independent of shaded

air temperature, as expected in a heliotherm? The populational dis-

tribution on the islands should be examined in terms of habitat types

available and any variation in mean Tb with vegetational density

determined. The iguana distribution (before the beginning of the study)

was minimally affected by introduced mammalian competitors, since the

human population was small and the only other mammal was the introduced

Norway rat.

Continuous Tb records of free-ranging lizards provide a large

amount of analyzable data, as shown by Stebbins and Barwick (1968) from

their monitoring of a single lace monitor lizard. Maximum and minimum

Tb's during the regulating phase, times of emergence and submergence,

and heating and cooling rates can easily be extracted from the record.

Then, many interesting questions can be addressed. How do the maxima

and minima vary during the day on clear days? Does body temperature

variability decrease as body weight increases? Does this variability

decrease as mean Tb increases? How is mean Tb related, if at all, to

reproductive state, sex, and size?

Heath (1964) and DeWitt (1967) were two of the first investigators

to report a significant temperature differential between the head and

body of lizards during heating and cooling, calling into question the

significance of measuring just cloacal temperature and bringing up the

question of what body temperature is regulated. Since then, many

workers have simultaneously measured more than one body temperature in

lizards (Johnson 1972, Webb, Johnson, and Firth 1972, Crawford 1972,

Spray and Belkin 1972, 1973, Crawford and Barber 1974, Parmenter and

Heatwole 1975, Pough and McFarland 1976, McNab and Auffenberg 1976,

Crawford et al. 1977). For a large lizard like Cyclura carinata,

multiple body temperature measurements are advisable as part of the

study. Head-gut and dorsal black body-gut-ventral body surface tempera-

tures were measured to determine internal temperature differences and

dorsal and ventral heat transfers with the environment, respectively.

Lizards had to be confined in outdoor pens to maintain continuous visual

contact, a serious problem with free-ranging lizards.

Two aspects of the ethological thermal biology of Cyclura

carinata are investigated. The first addresses the question of how

daily variation in the thermal environment and Tb influence lizard

activity. Lizard movement in burrows, emergence and submergence timing,

movement during the morning basking and regulating phases, feeding rate,

total food consumed, passage time of transmitters through the gut,

defecation timing, and secretion timing of the nasal salt gland are

considered. Lizards vary considerably in the amount of time spent

in actual motion. "Widely foraging" predators, such as varanids and

teiids, are generally more active than "sit and wait" insect feeding

iguanids (Pianka 1973). Herbivorous lizards should fall somewhere in

between, if they feed on a variety of plants, since they must go to

where the plants are located and then actively pick items up. The

partitioning of the lizard's active time between feeding, social, and

thermoregulatory movements should vary consistently between each of

these three dietetic categories. Ideally, a continuous time-motion

study should be conducted in the field, as accomplished for Egernia

cunninighamt by Wilson and Lee (1974). However, this proved impossible

from a fixed blind, due to vegetational density and the considerable

distance traveled by adult iguanas. Penned lizards were observed


The second ethological approach is to discover how Cyclura

carinata regulates its body temperature and then to compare this

behavior with that of other lizards, reported on extensively in the

literature. This has traditionally been the emphasis of lizard thermal

biology studies, since the time of Cowles and Bogert (1944). The roles

of thermoregulatory postures were comprehensively catalogued in a

qualitative manner, similar to Brattstrom's work on Amphibolurus

barbatus (1971) and Greenberg's on Sceloporus cyanogenys (1977).. Some

of the behaviors were quantified under controlled field and laboratory

conditions. A laboratory device was built to quantify the degree of

sun orientation and thigmothermia, using a photographic technique

similar to Heath's for Phynosoma (1965). I did not attempt to find out

to what extent body posture controlled T, under a defined set of
thermal conditions, as Muth (1977b) and Porter and James (1979) have

recently done.

Lizards usually heat faster than they cool (Bartholomew and

Tucker 1963, 1964, Morgareidge and White 1969, Weathers 1970, Weathers

and Morgareidge 1971, Weathers 1971, Baker et al. 1972, Ellis and Ross

1977). This is attributed to increased peripheral blood flow during

heating. The ratio of heating to cooling rate increases as body mass

increases in the American alligator, to the extent that while hatchlings

heat and cool at about the same rate, a 1000 kg adult would theoretically

heat nearly three times faster than it cools (Smith 1979). The testing

of Cyclura carinata is justified on comparative grounds and because of

its large size, especially since the data obtained complement the

heating and cooling rate results for the species in the field.

Many rate processes become somewhat temperature independent in

reptilian preferred Tb ranges (see Dawson 1975 for a review). Selected

physiological parameters--resting and maximum oxygen consumption, rest-

ing and maximum heart rate, and oxygen consumption during recovery from

maximum exercise--were measured in Cyclura carinata to see how they

varied with Tb. The study of recovery from maximum exercise was

especially interesting, since the amounts and kinds of voluntarily

tolerated, strenuous activity the species engaged in were observed in

the field. Bennett's methodology (1972) for his comparison of oxygen

consumption, oxygen debt, and heart rate in Varanus gouldii and

Sauromalus hispidus was closely followed, permitting comparison

with results obtained for Cyclura.


The field study site was located in the Caicos Islands, between

210 and 22 North latitude and 710 30' and 720 30' West longitude,

approximately 150 km north of Hispaniola and 890 km southeast of Miami,

Florida. Pine Cay was the base of operations, a privately owned island

with excellent lodging, potable water, an air strip, and a large popu-

lation of CycZuura carinata (as of August 1973). Field work was conducted

primarily on Water Cay, connected by a traversable sand bridge to Pine

Cay. Iguana density was adequate here at the beginning of the study, no

human habitation was present, and bulldozed paths provided easy access to

most areas at the northeast end of the island. The two islands are

located on the northern perimeter of the triangularly shaped Caicos

Bank, a shoal with a northern base of 125 km and a southerly directed

altitude of 75 km. Water Cay has an area of approximately 225 ha, with

a leeward northwestern sandy beach, a windward eastern rocky limestone

coast, and a southern mangrove swamp. The height and density of the

vegetation increases with island age and soil depth and quality from the

northwestern to the southeastern side of the island. The highest point

is approximately five meters above sea level.

I spent a total of 140 days in the field during four trips:

June 1-July 28, 1974; September 30-November 4, 1975; February 4-23, 1976;

and August 17-September 11, 1976.

Two field sites were chosen on the eastern end of Water Cay. Site I

was in level, sandy, Semiopen Scrub, 600 m from the NE side and 275 m from


the NW side of the island. Site II was in Dense Scrub, with Rocky

Coppice bordering the Pine-Water Cay inlet, 200 m from the SE corner of

the island (see Auffenberg, in prep., for descriptions of vegetation

types). Work was confined to approximately one hectare at each site.

Site I bordered a bulldozed road and Site II was crisscrossed by an

interconnected road network.

A moderately large hotel complex was completed on Pine Cay in the

summer of 1973. By the time of my first trip, iguana populations had

already declined on both Pine and Water Cays due to predation by man,

dogs, and feral cats. The subsequent collapse of the population on Pine

Cay has been documented by Iverson (1977). Cyclura density at Site II

was estimated at 10 adults per ha in July, 1974. Density was somewhat

less at Site I. Iguanas had practically disappeared from Site I by

September, 1975, necessitating a concentration of effort at Site II.

Iguanas had been extirpated from Site II by August, 1976, resulting in

a shift of field work further southwest along Water Cay and to Fort

George Cay, just north of Pine Cay. Due to the small number of hatchling

and juvenile iguanas, the study had to be restricted to adults.

Eleven male (X = 993 g, 435-1715) and four female (X = 748 g,

528-1135) iguanas were brought to Gainesville, where they were kept in

two outdoor galvanized sheet metal pens. One pen was circular, enclos-
ing an area of 16 m2, and the other was rectangular, enclosing 18 m2

Eight plywood boxes, each measuring 40 cm wide by 40 cm long by 10 cm

high, were perched on concrete blocks and provided shade, shelter, and

basking platforms. Substrates were beach sand and grass in the circular

and rectangular pens, respectively. From October 1 to March 30, the

pens were partially or completely covered with 4 ml polyurethane plastic

to increase temperatures. An electric forced air heater kept temperatures

above freezing on exceptionally cold nights. The captives were fed

bananas, green beans, white grapes, and fish-flavored catfood.

Several environmental variables were monitored in the field.

Measurements were taken hourly at a single location near the blind at

Sites I and II, where an open, sun exposed area bordered an area of

fairly dense vegetation. Changing temperatures between readings were

estimated to occur linearly. Substrate temperatures were taken on dry

sand with a Number 421 banjo probe attached to a Model 46 Tele-Thermometer

(Yellow Springs Instrument Co.). Air temperatures were taken at a height

of 2-3 cm with a Number 405 air probe. A black body for estimating

daily variations in solar heat input was constructed by placing a

mercury thermometer in a groove carved in a balsa wood block. The block

was then covered with a thin brass plate (0.4 mm) and coated with flat

black paint. A record was kept of the times the sun was obscured by

clouds. Light intensity was measured with a Type 213 light meter

(General Electric) directed from a height of 20 cm at a piece of white

painted cardboard placed on the ground. Instantaneous wind speed was

measured with a Dwyer wind meter. Average wind speed was determined

over a one minute period with an Air Meter Model W131 (Weather Measure

Corp.). Relative humidity was measured with a sling psychrometer.

Core body temperatures of free-ranging iguanas were measured with

Model L far-field transmitters (Mini-Mitter Co.). The transmitter was

a crystal-controlled blocking oscillator operating in the citizen's

band range (27 MHz). Osgood and Weigl (1972) describe the circuit diagram

and construction. The signal, a series of beeps increasing in frequency

with temperature, was received with a Model HA-420 three-channel walkie-

talkie (Lafayette) with an attached beat frequency oscillator. Trans-

mitter range was approximately 200-300 feet, depending on the topography.

Accuracy was + 0.5 C. The transmitter was powered by two hearing aid

batteries (Mallory MS 76), which had a working life of one to two months.

The transmitter was embedded in epoxy resin and enclosed in a plastic

capsule. The capsule was then coated with a mixture of 50 percent

paraffin and 50 percent beeswax, followed by dental acrylic (NuWeld,

I.D. Caulk Co.). The package weighed about 15 g and was smaller (1.7 by

3.7 cm) than a CycZura egg. A single mercury thermometer (Scientific

Products), checked for accuracy against a NBS certified bomb calorimeter

thermometer (Parr Instrument Co.), was used to calibrate all transmitters

used in this study. Most transmitters were recovered after the monitor-

ing period. Drift never exceeded 0.5 C.

During the summer field trip of 1974, a transmitter was implanted

in each of eight adult iguanas. The operation was performed during the

night of the day of capture. The lizard was fastened to a wooden jig

similar to that used by Bartholomew and Tucker (1963). The individual

was then placed in a large freezer cabinet until body temperature had

fallen to 2-5 C. Tb was monitored intestinally with a Tele-Thermometer

Probe Number 701 inserted approximately 10 cm into the distal colon

and taped to the tail. The individual was kept on ice during the

operation. The transmitter was inserted through a dorsoventral

incision made on the right lateral abdominal wall about 1 cm anterior

to the rear leg. The incision was closed with nylon fishing line.

Individuals were released the day following the operation and monitored

immediately. During subsequent field trips, transmitters were placed

in the gut immediately after capture. A gauze pad soaked with halothane

(Ayerst Laboratories) was positioned at the bottom of a 250 ml beaker.

See McDonald (1976) for a discussion of this inhalation anesthetic. The

beaker was then slipped over the lizard's head. A rubber apron taped

to the mouth of the beaker extended over the forelegs, reducing the rate

of loss of gas anesthetic. Lizards were usually apneustic when the mask

was initially placed over their heads, the duration of apnea being

inversely correlated with body temperature. The drug took effect within

a minute after breathing commenced. Complete anesthesia lasted between

five and ten minutes, and recovery was seemingly complete within an hour.

All individuals were weighed (Ohaus Dial Spring Scale), measured (snout-

vent and total length), examined for scars and ectoparasites, and marked

on both sides of the trunk with a bright orange Arabic numeral (Aero-

gloss paint, Pactra Industries).

The body temperatures of eleven different, free-ranging adult

iguanas were monitored during the study (10 males, 1 female). Two males

were monitored on two separate trips. Recording periods extended from

three to twenty days. Temperature readings were taken every five to

fifteen minutes from before the individual emerged up to two hours

after it submerged for the day.

I observed and monitored iguanas from a blind during the first

field trip. Lizards were attracted to the vicinity with a sardine bait

and noosed from inside the blind. Less timid individuals were noosed

without bait and blind.

Iguanas were less timid during the second and third trips, per-

mitting more thorough observation of specific individuals by continuous

tracking (6 adult males tracked 1-6 days, X = 4 days). Following initial

transmitter placement, iguanas were monitored without further visual

contact until the start of the second or third day. Since iguanas

usually retreated into their burrows when disturbed during the initial

basking period, visual contact was always delayed for a time after

emergence. I crawled along behind the lizard at a distance of approxi-

mately five meters during its feeding forays. Visual contact was

intermittently lost when the individual moved off into dense scrub. The

lizard was usually quickly resighted by following the same direction of

travel. Signal strength, as perceived by the human ear, reached a

maximum approximately three meters from the transmitter. Bushes along

the route of travel were flagged with orange plastic tape marked with the

date and time. A crude map of the route was recorded in a notebook,

along with observations of the individual's behavior. The locations of

the flags were later marked on a detailed map of the site. Average

rates of travel and distances traveled could then be calculated at


Near-field transmitters, built according to Mackay (1970), were

used during the study. They were cylindrically shaped, measuring approxi-

mately 1 by 3 cm and weighing 4 to 6 g. The signal, a series of clicks

increasing in frequency with temperature, was received at a maximum

distance of one meter with an AM transistor radio (50-160 KHz). The

package was sealed in the same manner as the far-field transmitters.

Iguana movement in the burrow and Tb were monitored

simultaneously during the second and third trips by placing both a

near-field and a far-field transmitter in the gut of a single large male.

After the lizard submerged for the night, its position was located by

moving the AM radio to where the signal was strongest. The radio was

again placed directly over the lizard early the next morning prior to

emergence. The signal was monitored at the blind six to nine meters away

from the burrow by listening through an earplug connected to the radio.

When the lizard moved, indicated by fading or loss of the signal, I

quietly moved the radio to the lizard's new position and returned to the

blind. This procedure was repeated until the lizard emerged. To see

how far it would submerge, the lizard was deliberately scared into its

burrow at different times of day. The location of the burrow terminus

was determined by digging at the end of the monitoring period.

In June of 1974 body temperatures of four iguanas were monitored

two at a time in two field cages at Site I. The cages were constructed

of quarter inch hardware cloth in the shape of a cylinder 1 m high

by2 m long. Two, 15 cm diameter, 1 m long cylinders were attached to

one end of each cage and covered with sand to simulate burrows. Shellac

coated copper wire was wrapped around the entire cage to act as an

antenna for the near-field transmitters. Strands were approximately

10 cm apart. Each two leads were attached to a circuit breaker connected

to two similar leads from wire wrapped around the ferrite antenna of the

AM radio. Thus, monitoring the Tb of one lizard could be immediately

followed by monitoring the second by switching circuits. Individuals

were kept in a complex habitat during the first four to seven days.

One-half of the cage was covered with thatch palm fronds and branches

were arranged beneath the fronds inside the cage,allowing the iguana

to get nearly one meter off the ground while still remaining in the

shade. The burrows provided the only shade during the next two to three

days of monitoring, in what was called the simple habitat. The body

temperatures of two caged and two free-ranging iguanas could be monitored

simultaneously from the blind.

Preferred T''s were determined in two thermal gradients constructed

of plywood, each 2.2 m long, 0.4 m wide, and 0.6 m high, with tops

covered with quarter inch hardware cloth. Two 250 w heat lamps were

suspended at one end of each gradient; their height was adjusted so that

the black body temperature immediately beneath them was 60 C, slightly

below the lowest monthly maximum recorded in the field (63 C in February).

The gradients were placed in a controlled environmental room (Environ-

Room, Lab-Line Instruments, Inc.) set at an air temperature of 25 C (+ 1.0

C accuracy, air velocity next to the lizard less than 0.25 m/second).

The air temperature in the cool end of the gradients gradually increased

to a maximum of 28-30 C after four hours of the eight hour photoperiod.

The photoperiod was centered at 1200 EST. A 40 w fluorescent bulb

provided less than ten footcandles of illumination. Preferred Tb's

were determined for eight adult iguanas, a group of four acclimatized

to Gainesville temperatures both in July-August and December-January.

Summer and winter lizards were monitored individually, for four to

eight consecutive days, respectively. Monitoring commenced the day

following transmitter placement. Lizards received neither food nor

water while in the gradient.

Low body temperature behavior was examined in six adult CycZura

acclimatized to Gainesville temperatures in May. Starting at 1200-1600

(all times reported in this study are EST), the individual was cooled in

the environmental room set at an air temperature of 5-8 C. Body tempera-

ture was monitored colonically with the Tele-Thermometer. The losses of

seven behavioral responses were noted as T decreased: 1. crawling,

2. turning over when placed on the back (critical thermal minimum),

3. maintaining a horizontal head orientation when the body was rotated

about its long axis, 4. maintaining a constant field of view by rotating

the head or eyes when the body was rotated laterally, 5. moving the legs

when pinched while resting on the back, 6. bloating, and 7. closing and

opening the eyes. Each lizard was cooled an additional 3 C, then exposed

to room temperature outside the environmental room. The lizard's body

temperature was again recorded as each of the seven behavioral responses

was regained.

To examine the timing and degree of heat transfer through the dorsal

and ventral surfaces of the iguana's body, three-transmitter experiments

were run in a circular Gainesville pen in late August and early

September. Two far-field transmitters were fastened with electrician's

tape to the outside of a piece of television antenna cable. When the

cable was wrapped around the lizard's waist just anterior to the rear

legs, the transmitters were situated ventro-laterally on either side of

the trunk. The cable ends were held together dorsally with a rivet.

The temperature-sensitive thermistor bead, embedded in epoxy resin, was

located at the end of a short probe wire extending from one end of the

transmitter. One probe tip was taped to the middle of the ventral side

of the cable, to monitor the body-substrate interface temperature

immediately under the lizard. The other, painted flat black to monitor

dorsal heat input, was suspended free in the air about 1 cm anterior

to the cable and 5 mm above the middle of the lizard's lower back.

A near-field transmitter was placed in the lizard's gut. Three large

males (1195, 1240, and 1260 g), monitored one at a time for a total of

nine days, moved freely about the pen. Seven other iguanas were also

present. Readings from the three transmitters were taken every five to

ten minutes. To obtain gut temperature readings, the AM radio was taped

to the end of a wooden pole and extended from outside the pen to within

a meter of the lizard. Shaded air, sun-exposed sand, and black body

temperatures were also measured. The lizard's behavior was observed

and notes taken for later correlation with the transmitter records.

To determine whether feeding rate or meal size was significantly

less immediately after morning emergence than during the higher T 's of

the regulating phase, iguanas in the Gainesville pen were presented with

known weights of white grapes. Food was either placed on trays on the

ground, before individuals emerged for the day, or on trays affixed to

the tops of posts, after individuals had reached regulating phase body

temperatures. The elevated trays were large enough for only one

individual to sit on, preventing feeding by several animals on a single

known weight of grapes. Also, by placing grapes on three post tops

simultaneously, one feeding lizard was rarely displaced by another.

Animals were fed on clear days after at least two days with no food.

Sun orientation directions of lizards were measured with a hand

held Silva compass. Records were obtained in the field, the Gainesville

pen, and a 2 m circular arena placed on top of the zoology building. To

determine the importance of vision in sun orientation control, lizards

were blindfolded by placing ellip-tically shaped plastic disks over their

eyes and securing the disks with several layers of electrician's tape

wrapped around the head. A stretch sock, with an opening for the

nostrils, was then placed over the head and taped at the neck to prevent

the lizard from scratching off the tape.

A photothigmotron was built to quantify thermoregulatory postural

changes in Cyclura. A square plywood substrate box, measuring 65 by 65

by 5 cm, was lined with Plexiglas and sealed internally with fiberglass

cloth and resin. A 0.3 mm thick aluminum sheet formed the top of the

inner Plexiglas box and was affixed to it with Al-40 adhesive (Devcon).

A grid of 1 cm squares was scored on the exposed surface of the

aluminum. The substrate box rested on a 15 gallon water bath

(Precision Scientific Co.). The water bath pump was connected via

Tygon tubing (Norton Plastics and Synthetics Division) to two ports

drilled in the side of the substrate box. Water at the desired tempera-

ture was pumped through the entry port in the substrate box and circulated

evenly via six inner exit ports pointed in different directions. A small

hole was made at one corner of the aluminum top to permit pressure

equalization when the pump was initially turned on. A short tube was

attached externally to the rim of the hole to prevent water overflow.

To confine the lizard to the aluminum substrate, a one meter high hard-

ware cloth cage, reinforced with wooden frames at top and bottom, was

placed on the substrate box. The cage top was covered with a Plexiglas

sheet, on which was placed a 35 mm camera directed downward toward the

aluminum grid. A single 250 w heat lamp, attached to a tripod resting

on the floor, was directed slightly downward toward the side of the cage.

The observer's side of the cage was covered with vinyl plastic provided

with a small observation port. The photothigmotron was placed inside

the Environ-room.

Before each iguana was introduced into the photothigmotron,

several body areas were determined. The lizard was anesthetized with

halothane and placed on a Plexiglas sheet. Outlines of the outer edge

of the body and the inner area of substrate contact were marked on the

sheet and later transferred to a piece of paper. Three separate

measurements of each area were made planimetrically and the mean taken.

Contact area of the anesthetized lizard was assumed to equal maximum

contact of the free-ranging lizard. The day before the first experiment,

the lizard was placed on an insulative piece of plywood resting on top

of the aluminum substrate of the photothigmotron. One experiment was

performed each day, starting at midday. The photoperiod was ten hours.

Animals were kept in the cage for three to five experiments, during

which they received neither food nor water. An hour before heating or

cooling of the lizard began, the water bath pump was turned on to bring

substrate temperature to the desired level. The plywood was then

gently removed, shifting the individual onto the metal substrate. The

heat lamp was also turned on in some experiments. Photographs of the

dorsal aspect of the lizard were taken at intervals. Core body tempera-

ture was measured with a near-field transmitter placed in the digestive

tract. The extent of leg and tail contact was noted, as well as how

much of the anterior trunk was elevated off the substrate. The black

and white photograph negatives were projected with a slide projector

onto a piece of white paper and the body outline traced. The dorsal

outline area was determined planimetrically. Head, anterior trunk, leg

and tail noncontact areas as well as a standard correction based on the

difference between the inner and outer outlines of the anesthetized

lizard were subtracted from the dorsal outline area to get the approxi-

mate contact area. This value could then be converted to a percentage

of the maximum possible contact.

Head temperature was measured at two different locations, using

probed near-field transmitters. The transmitter was taped to a piece

of television antenna cable fastened with a rivet around the lizard's

neck. In a large male monitored in the photothigmotron, the thermistor

probe was inserted into the orbital venous blood sinus through a 1 mm

diameter hole drilled in the skull. The probe wire was glued to the

center of a circular cork disk, which was glued to the top of the head

with epoxy resin. Initial placement of the probe resulted in a temporary

eye bulging (also noted during cannula placement in Phrynosoma cornutum

by Heath 1966). In a second large male, monitored in the arena atop the

zoology building, the probe tip was placed just inside a slit made in

the tympanic membrane. The probe wire was glued to a plastic disk, which

was glued to the outside of the tympanum. Lizards were allowed to

recover from implantation for three days before testing.

Skin reflectivity was determined for two Cyclura adults from Water

Cay, one in the light and one in the dark color phase. The light phase

lizard was killed by heating it above the lethal maximum body tempera-

ture and the dark phase lizard died of starvation. Epidermal-dermal

squares, measuring approximately 25 mm on a side, were removed from the

lizardsimmediately after death and placed onwater-moistened filter paper.

Patches were taken from the mid-dorsal, ventral pectoral, and ventral

abdominal trunk and the dorsal and ventral tail just distal to the anus.

Integumental reflectivities were immediately determined, using a Bausch

and Lomb Spectronic 20 Spectrophotometer with reflectometer attachment.

Monochromatic reflectance was obtained at a 90 angle to the skin surface,

using a magnesium carbonate block as a standard. Readings were taken

between 340 and 960 nm at 20 nm intervals. Reflectivity over the same

range was also determined for a common substrate on Pine and Water Cays,

fused corralline sand covered with two species of blue-green algae.

To check for possible reflectance of near-infrared light (700 to

900 nm) from the integument of live Cyclura, two adults were photographed

during daily activity in Gainesville, using Kodak Infrared Ektachrome

film (Schwalm et al. 1977). When the camera lens is covered with a

yellow filter, reflected near infrared light appears red in the developed


Skin patches were heated from different angles to determine whether

the rate of integumental heating decreased as the radiant heat shadow

caused by scale imbrication increased. The patches were removed from

various locations on a single adult iguana, tacked to separate pieces

of plywood, dried, and cooled to 20 C in a controlled environmental

room. A YSI Probe 421 was placed under the patch to monitor the time

required to heat the dried skin to 50 C with a 250 w heat lamp. Each

patch was heated 11 times, with the lamp at a constant distance of 17 cm,

oriented normally to the skin and at 15, 30, 45, 60, and 750 from normal,

both directly anterior and posterior to the imbricate edges of the

scale rows.

The histological structure of integumental "sensory spots"

(Miller and Kasahara 1967) were examined in tissue sections prepared for

light microscopy. Material had been fixed in formalin and transferred

to isopropyl alcohol for preservation at the Florida State Museum.

Tissue blocks were taken from the lizard's rostral, labial, parietal

eye, and dorsal tail regions, dehydrated in ethyl alcohol, embedded in

methacrylate plastic, and sectioned at 5 micrometers thickness vertical

to the skin surface. Sections were mounted serially and stained with

Mayer's hematoxylin and eosin-phloxine.

Six adult iguanas were heated and cooled in a controlled environ-

mental room (Environette, Lab-Line Instruments, Inc.). Each individual

was habituated for one day to its small hardware cloth cage, placed in

one Environette set at an air temperature of 20 C. Polyurethane panels

enclosed three sides of the cage, reducing the air flow over the lizard's

body surface to practically zero. The cage floor was also composed of

polyurethane. On the second day a YSI rectal probe, coated with petroleum

jelly, was inserted into the lizard's large intestine to a depth of 7-10

cm and taped to the tail. The cage was then rapidly moved to another

similarly wind-baffled box in another Environette set at an air tempera-

ture of 40 C. When within 1-2 C of ambient air temperature, the lizard

was rapidly transferred back to the 20 C Environette and cooled. During

the third and final day in the chamber, the individual was secured in a

supine posture to a wooden jig. The lizard's legs were free to move.

A rectal probe was again inserted into the intestine and a banjo probe

glued middorsally to measure body surface temperature. The individual

was then heated and cooled again. Animals were observed continuously

during heating and cooling through an observation port in the chamber

door. Breathing rates were recorded intermittently. The photoperiod

was ten hours. Heating began at 1300 and cooling was always over by

2100. Lizards were weighed at the start and the end of the test period

and given neither food nor water.

Heart rate and oxygen consumption at rest, during maximum activity,

and during recovery from exhaustive exercise were determined for five

adult iguanas (two females and three males; X = 1252 g, range = 834-1722).

Each lizard was tested on six consecutive days, starting at an air

temperature of 15 C and increasing at 5 C increments to a maximum of

40 C. Experiments were conducted after 2100 on individuals which had

received neither food nor water for two days prior to the first run.

After each run the chamber air temperature was elevated five degrees

for the next night's run. When not being tested, animals were permitted

to move freely about the 1.4 by 2.5 m Environ-Room, kept on a 10L:14D


The lizard's exhaled air was trapped in a rectangular, black-

painted Plexiglas mask fitted over the head. The mask had a neoprene

apron glued to its open posterior end, which fitted over the lizard's

anterior trunk and forelegs. Room air was sucked into the open posterior

end of the apron, past the lizard's head, and out the front of the mask

via Tygon tubing through columns of soda lime and Drierite, to remove

carbon dioxide and water vapor, respectively. Flow rates ranged from

280 to 2440 cc/min. The gas then passed through a flowmeter, a pump,

another flowmeter, and finally through a Beckman C-2 paramagnetic oxygen

analyzer, located outside the Environ-Room. Gas flows were measured

with rotameters calibrated with a Brooks Vol-U-Meter. The decrease in

percent oxygen resulting from the lizard's respiration was recorded

continuously, except during the exercise period, with a Honeywell

Electronic 15 stripchart recorder. Lizards were kept in total darkness

during all oxygen consumption measurements. Oxygen consumption was

calculated from oxygen content and flow rate data using the appropriate

equation given by Depocas and Hart (1957).

For each run, a rectal YSI probe was inserted into the lizard's

intestine. The animal was then fastened in a supine posture to a wooden

jig, with its head resting inside the mask, taped to the jig. Oxygen

consumption was monitored until a stable resting rate was achieved.

The lizard was then removed from the jig and mask and exercised by hand

manipulation for several minutes, sufficient to completely exhaust the

animal. The lizard was immediately refitted into the mask and refastened

to the jig. ECG needle leads were pushed beneath the skin of the shoulder

and the base of the tail. Heart rate was measured every 4-10 minutes of

the recovery period with a Physiograph Four A with high gain preamplifier

(E and M Instrument Co.), located outside the Environ-Room. When

oxygen consumption again fell to the resting rate, the lizard was

manipulatedbyhand for another two minutes to get a maximum heart rate



Climate of Water Cay

The Caicos Islands are in the northern tropical zone, slightly

below the Tropic of Cancer. They are also in the tropics under the

KIppen System (Koppen 1923), since mean monthly shaded air temperature

never falls below 18 C. Water Cay has a trade wind littoral climate,

with fairly uniform high temperature and distinct wet and dry seasons.

Figure 1 summarizes the black body temperature measurements taken

during three trips to Water Cay. CycZura had to remain intermittently

in the shade on sunny days during a large portion of its activity period

or face lethal body temperatures due to radiant heat input. Adult

lizards provided with some well timed overcast periods could theoret-

ically survive in an exposed location all day in at least October to

February. Yearly photoperiod varied by almost three hours, reflected

in the difference in width of the heating curves for February vs. July.

Figure 2 illustrates the annual air temperature cycle near the

two primary locations where Cyclura was observed. The range of mean

shaded air temperature was only 4.5 C on Grand Turk. Of course, both

daily and seasonal microclimatic extremes at ground level were greater.

Gainesville, located in the subtropics, was too cold part of the year

to support a Cyclura population. From the beginning of April until

the end of September, penned Gainesville lizards ate readily and gained

weight. Feeding was negligible during the other six months of the year.






- 44


7 8 9 10 II 12 13 14 15

16 17 18


Black body temperatures in the field. February, June, and
October measurements are represented by solid, dashed, and dotted
lines, respectively. Maximum temperatures during the recording
periods are represented by open squares, mean temperatures for the
hourly intervals by open circles, and minimum temperatures by
solid circles. All weather conditions encountered were included
in the calculations. Horizontal lines are means and vertical lines
are ranges of regulating phase Tb's of lizards at Site II for
February, July, and October, respectively.





Figure 1.

I 1 I I j I I I I I I I


I j


, I






- I






I -

- I

-4 1


Figure 2.

Air temperature in the shade at Gainesville, Florida (Agronomy
Farm Weather Station; 290 40' N, 820 20' W; Prine 1977; and
Grand Turk, British West Indies (Auxillary Air Field; 210 26' N,
710 8' W). Vertical lines extend from the maximum to the
minimum recorded Ta each month (dashed line for the year 1976
at Gainesville, solid line for the years 1900-1968 at Grand Turk).
Horizontal lines are mean monthly temperatures on Grand Turk.
Circles and squares represent mean maximum and mean minimum air
temperatures, respectively. Air temperatures were measured in
a standard NOAA shelter (Stevenson screen) at a height of 1.5 m.





Special precautions had to be taken to prevent the lizards from freez-

ing to death between November and February.

An easterly wind blew almost continually over the islands. The

mean surface wind speed on Grand Turk was 24.6 km per hour (15.3 mph).

Figure 3 illustrates the mean maximum July wind speeds on a road pro-

tected on the windward side by a limestone ridge and dense scrub at

Site II. Wind speeds were greatest during the middle of the day, a

typical pattern (Geiger 1957). Wind speed was greater at 50 cm than

at 3 cm above the ground, also a typical pattern. Thus, lizards basking

or feeding above the ground were usually cooled at a greater rate by

forced convection than lizards on the ground. Wind speed was consider-

ably higher facing the inlet between Water and Pine Cays just a few

meters away. Since lizard burrows were common near the top of the

ridge, some interesting wind related behavior was expected there,

perhaps similar to the seeking out of minimal wind exposure at low

Tb and maximum exposure at high Tb as seen in Amblyrhynchus cristatus

of the Galapagos Islands (Bartholomew 1966, Bartholomew et al. 1976).

Rainfall was distinctly seasonal in the Caicos (Figure 4). Mean

annual rainfall on Pine and Water Cays was probably slightly greater

than on Grand Turk (597 mm or 23.5 inches). Four seasons characterize

the western islands of the Caicos; a cool dry winter from January to

March, a warm dry spring from March to May, a hot, increasingly wet

summer from June to October, and a warm, wet autumn from October to


Water Cay was fairly humid (Table 1). Daily relative humidity

decreased as air temperature increased, minimizing near midday. Of

I II 1


8 9 10 II 12 13 14

15 16 17

Mean maximum wind speed at Site II in July. Ten consecutive
wind speed maxima were measured each hour for seven days at
3 cm (open rectangles) and 50 cm (solid rectangles) above the
ground. Horizontal lines are means, vertical lines are ranges,
and rectangles are plus and minus two SE of the mean.

1 I
l i I









1 I
I 1

Figure 3.






70 F



o il I II I I I I I I


Monthly precipitation on
line represents the mean
Total rainfall per month
Islands, are represented

A S 0 N D

Grand Turk, British West Indies. The
monthly rainfall for the years 1900-1968.
for several months on Pine Cay, Caicos
by dots.

Figure 4.

Table 1. Daily variation in relative humidity. Measurements
taken during hours of precipitation were not included.
Data were collected at Site I (Jun) and Site II (Feb,
Jul, Oct) on Water Cay.

N=4 N=12 N=15 N=7 DAYS

0700-0759 75 74 86
0800-0859 78 74 71 77
0900-0959 67 69 64 69
1000-1059 66 62 64 64
1100-1159 66 59 61 62
1200-1259 60 59 64 62
1300-1359 61 64 63 59
1400-1459 62 61 64 64
1500-1559 66 61 65 66
1600-1659 70 67 71 70
1700-1759 73 72 71 78

RANGE 23 34 28 25

MEAN MONTHLY RH 66.0 64.6 66.9 68.0
2SE 2.1 1.4 1.5 2.4

course, daily absolute humidity did not vary as much as relative

humidity. Mean monthly relative humidity did not differ significantly

between February, June, July, and October.

Diel Body Temperature Cycle of a Heliothermic Lizard

The body temperature cycle was divided into four phases by Wilson

and Lee (1974). Some slight alterations were made for the following

scheme (Figure 5).

1. Morning Heating Phase The lizard emerged from its burrow and

heated rapidly in direct sunlight. Cyctura usually started its first

feeding foray below the first maximum Tb, upon reaching the "normal

activity range" (Cowles and Bogert 1944). Wilson and Lee's "basking

phase" ends here. This term is confusing since basking did not cease

when the first feeding foray began. Also, Cyclura was so wary during

the June-July trip that it was very difficult to observe the start of

the first foray unless I was sitting in a well positioned blind. There-

fore, the first phase has been called the morning heating phase, ending

at the first maximum Tb. This endpoint is obvious on a continuous Tb


2. Regulating Phase Tb fluctuated between a series of maxima and

minima, staying within a fairly narrow range.

3. Burrow Cooling Phase It started at the lizard's evening

submergence and ended during the night, when T, had fallen to the 24

hour minimum. The decline in Tb followed a Newtonian cooling curve,

with an ever decreasing rate of Tb decline as the stable deep burrow

temperature was approached.


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4. Stable Tb Phase The lowest Tb in the 24 hour cycle occurred

just before emergence in two lizards larger than Cyclura carinata, the

Lace Monitor, Varanus various (Stebbins and Barwick 1968) and the Komodo

Dragon, Varanus komodoensis (McNab and Auffenberg 1976). However, Tb

stabilized considerably before emergence in Cyclura, necessitating a

fourth descriptive phase. The term "inactive phase" used by Wilson and

Lee would be confusing since Cyclura was also inactive in the burrow

cooling phase.

A continuous body temperature record provides a substantial amount

of information about a lizard. It was sometimes difficult to determine

the exact time of emergence from the record, since deep burrow tempera-

ture was slightly greater than surface temperature early in the morning.

The lizard in Figure 5 may have lost heat on the surface just after

emergence (A) or near the burrow mouth prior to emergence (B). Slight

differences in emergence Tb could sometimes be used to determine the

burrow the lizard spent the night in, without having to locate the

burrow the preceding night by following the increasing signal strength

with the receiver. The time of submergence (F) is easily discerned in

the February record. However, determination of submergence time from

the summer records was commonly more difficult, since Tb often fell

prior to submergence and at a rate not easily distinguished from the

initial decline after submergence. Body temperature shifted abruptly

upward as the overcast cleared temporarily at (D), a change maintained

until submergence. Shifts of this sort were fairly common in the records.

Several further terms concerning lizard Tb need to be defined.

All refer to measurements on a single individual taken during its

regulating phase. Unless otherwise specified, each Tb reading used in

a calculation occurred during a period of sunshine or overcast (10

minutes or less) which did not cause a decline in Tb.

1. Mean Daily Tb Once the continuous record for a single day

was plotted, the first and last maxima plus points at fifteen minute

intervals, on the hour, were averaged.

2. Daily Minimum, Maximum Tb The lowest, highest Tb recorded

for the day (C and E, respectively, in Figure 5).

3. Mean Daily Minimum, Maximum Tb An average of the daily

minimum, maximum Tb for a specified number of days.

4. Mean of Daily Tb Minima, Maxima An average of all minima,

maxima for one day.

5. Mean of Tb Minima, Maxima An average of all minima, maxima

for a specified number of days.

Regulating Phase Body Temperature in the Field

Cyclura carinata is a stenothermal lizard during the regulating

phase (Table 2). The mean of the regulating phase Tb ranges for all

the monitoring days during clear weather was only 3.3 C (SD = 1.3,

range = 0.7-6.4, N = 106 days). The frequency distribution of these

Tb ranges was positively skewed toward greater stenothermality, with

a median of 2.9 C and a modal class of 2.0-2.4 C.

Adults rarely went into their burrows at Sites I and II because

of extremely high surface temperatures, although this may have been a

common behavior in more sparsely vegetated areas. Free-ranging lizards

prematurely submerged for the day on only 19 occasions during 129

individual monitoring days: 45 percent due to rain, 40 percent due to


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human disturbances, and 15 percent due to extreme cloudiness. Rates of

cooling during burrow excavation and shade sitting were not consistently

different. Thus, the cause of the cooling could not be determined by

examination of the Tb record alone.

Figure 6 summarizes the regulating phase data for all the field

lizards. The rise in mean Tb over the 3.5 C range was steady. Minimum

Tb's fell into two groups having no correlation with increasing mean

Tb's, one group above and one below 39 C mean T,. This probably is of

no significance. The correlation of maximum Tb with mean Tb was better.

The lowest maximum Tb recorded was 1.6 C above the highest minimum. Thus,

all T ranges of individuals overlapped somewhat, no matter what the

sex, habitat type, or season of measurement.

The sample sizes were too small to determine conclusively whether

or not mean Tb differed significantly with sex. Lizard 9, a dominant

male, had a significantly higher Tb than Lizard 8 (p < 0.05), an adult

female monitored simultaneously. However, two of three caged females

in the simple habitat, Lizards 4 and 5, had significantly higher body

temperatures than the caged male, Lizard 7. Mean T 's were not

significantly different in two free-ranging males and a female monitored

at Site II in February.

Gravid females may have lower regulating phase T 's than spent

females and males. The gravid June female (Lizard 6) had the lowest

mean Tb of all those monitored. The means were significantly higher

(p < 0.05) for the other two caged females (Lizards 4 and 5) and the

free-ranging female (Lizard 8) at Site I, all of which had probably

recently laid eggs, since they actively defended their burrows against

both encroaching males and females. However, Lizard 6's Tb was not

aC 3 4a 4-
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significantly lower than the caged male, Lizard 7. On the single day

Lizard 6's Tb was recorded after egg laying, the maximum was 0.5 C

higher than the highest maximum of the seven monitoring days previous

to laying. The highest mean Tb recorded was on the day she laid her

eggs, but the mean was not significantly higher than the next two

highest means recorded prior to laying. The differences probably

would have been significant had not the day of laying been overcast

50 percent. of the time.

Temporary Hyperthermia and Hypothermia

All eleven iguanas monitored in the field passed through a period

of hyperthermia soon after release (Figure 7 and Table 3). Tb then

declined to a more stable, presumably normal range. The Tb decline

was either rather rapid as for Lizard 3 or more gradual as for Lizards

8 and 11. The extent of the hyperthermic response, as measured by the

sum of the ranges of the maximum daily Tb and the mean daily Tb's

between the hyperthermic peak day and the return to normalcy, was

usually slightly greater in coelomically than enterically implanted

lizards. However, the response may vary with season as well as with

transmitter location. The summer animals were probably suffering

from a bacterial infection resulting from transmitter implantations

(see Vaughn et aZ. 1974, Kluger et al. 1975, and Bernheim and Kluger

1976a, b for related laboratory studies). The second Tb rise observed

in Lizards 8 and 9 may have been due to reinfection of the wound or

a secondary response to a chronic infection. In the latter case it

may be that lizards could not tolerate a high Tb for more than a few

days even though infectious agents were still present (Cowles and

c o *a 1
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cc cu u
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r. 0 r) %W
bd M CO 0

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la pg to a
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and Burleson 1944, Licht 1965b, Licht and Basu 1967, Kluger et aZ.

1975). The body cavity internal to the wound sites and surrounding the

transmitter suppurated only slightly or not at all at the time trans-

mitters were removed. The mean time between release and the maximum

hyperthermic response was 2.4 days in summer Cyclura and 1-2 days in

Dipsosaurus injected with live Aeromonas bacteria (Bernheim and Kluger

1976a). Recovery was complete in Dipsosaurus by the sixth day after

injection and, on the average, by the seventh day after the operation

in summer Cyclura. These similarities may signify that similar dis-

ruptions were in force in the brain thermoregulatory centers of both

species. Hyperthermia in enterically implanted lizards may have been

a feeding response to a transmitter meal or, somehow, a reaction to

handling or the use of halothane. The lizard with the weakest response

was Number 6, the gravid caged female. Embryonic development in Cyclura

carinata begins within the female's body and continues after nesting

at burrow temperatures of 28-29 C (Iverson 1979). Regulating phase

T 's in the range of nongravid lizards may be fatal to developing

embryos in Cyclura, as they are in Iguana iguana (Licht and Moberly

1965). Thus, the hyperthermic response to bacterial infection may

have been counterbalanced somewhat by a hypothermic response to


Hyperthermia also occurred in the laboratory thermal gradient

(Figure 8). The high daily mean Tb was significantly greater (p < 0.05)

than the low in six of eight animals. The hyperthermic responses in

the field and gradient were fairly similar; that is, a latent period

of variable duration was followed by a maximum Tb and a decline. High

mean Tb occurred in three species of Phrynosoma when first housed in

Patterns of regulating phase body temperature and
distance traveled in Cyclura carinata in a laboratory
thermal gradient. Data are presented for eight
lizards, each monitored for four consecutive days.
Lizard 3 was included in both samples. Horizontal
lines are Tb means, vertical lines are ranges, and
open rectangles are plus and minus two standard
errors of the mean. The total distance each lizard
walked (open circles) was measured during the full
eight hour photophase.

Figure 8.

2 3 4














10 w





terraria (Heath 1965) and in Anotis carolinensis when first introduced

into a thermal gradient (Licht 1968). The authors believed the hyper-

thermia, which ceased after two days, was due to lizard inexperience in

new surroundings. Learning the new thermal environment resulted in a

decline in Tb to the preferred level. The same explanation probably

applies to Cyclura. Four of eight lizards did not move voluntarily

during the first day. Two of the lizards were located under the heat

lamps when the photophase began. It was thought best to push them

toward the cool end of the gradient when they began to pant. The steady

increase in walking distance per day corresponded in part to learning

how to maintain preferred Tb by shuttling.

The hyperthermic response, as measured by the difference between

the maximum mean daily Tb minus the mean preferred Tb, is similar in the

iguanid lizards studied to date: 1) 2.0 C in Anolis carolinensis by the

third day in a thermal gradient (Licht 1968), 2) 2.3 C in field monitored

and 2.2 C in gradient monitored Cyclura carinata, 3) 3.7 C in Dipsosaurus

dorsalis on the second day after injection of dead Aeromonas hydrophila

(Bernheim and Kluger 1976a), and 4) 2.9 C in Phrynosoma by the third

day in a thermal gradient (Heath 1965). One explanation for the

similarity in the responses is the constancy of the small temperature

gap between the preferred Tb and the CTM in these lizards.

Voluntary hypothermia during the regulating phase was a rare event,

observed in only two free-ranging summer lizards (8 and 10) on the day of

their release. Lizard 8 never ventured further than a meter from its

burrow the first day, retreating six times to the burrow for lengthy

cooling periods (Figure 9). As Tb maxima increased, Tb minima increased

also, resulting in a series of ascending peaks ending with the highest


0 1


10 1

ZS 0 L4

-i Mc
C 4-


,C C

NC a
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peak late in the afternoon. The same pattern was observed in only 2 of

51 thermal gradient records. Hypothermia in newly released field

lizards may have been due to a temporarily heightened thermal sensitivity

due to cooling to 3-12 C during the implantation operation the previous


The Relationship of Pertinent Environmental Variables
to Regulating Phase Body Temperatures


Table 4 summarizes the environmental temperature data accumulated

for Site II. Mean black body temperature was not significantly different

in February and October. The mean range was only 3.1 C between February,

nearly the coldest month, and July, nearly the warmest. The mean

differences between months for the other three temperature measures

in the table were significant. The ranking was also consistent. The

February-July mean temperature difference increased from 4.2 C for sun

exposed sand and 4.7 C for shaded sand to 6.5 C for shaded air. Although

the monthly percentages of time that clouds obscured the sun did not

differ significantly, the thickness of the cloud cover and the percent-

age of the sky in overcast were greater during the rainy season in

October than in February and July.

Mean monthly Tb did not correlate directly with changing monthly

environmental temperature. Mean Tb at Site II was significantly higher

in October than in February and July (p < 0.01, student's t test)and

mean Tb's in February and July did not differ significantly from each

other (Table 5). The seasonal variation in mean Tb was probably only

slightly greater than 0.5 C (July minus February mean). The significant

Table 4. A seasonal comparison of some environmental variables
at Site II on Water Cay. The data were collected at
approximately hourly intervals from 0900 to 1700.
Values are for a variety of weather conditions in
February (15 days), July (16 days), and October (16


October 191 44.1 45.4 42.8 64.4 27.0
February 109 44.2 46.1 42.3 63.0 24.1
July 181 47.2 48.8 45.6 67.4 28.3
February 101 33.4 34.9 31.9 >52.0 23.7
October 190 35.8 36.7 34.9 >52.0 25.1
July 177 37.6 38.5 36.7 >52.0 26.8
February 109 26.3 26.9 25.7 36.3 21.4
October 192 29.1 29.5 28.7 39.6 25.1
July 182 31.0 31.3 30.7 35.5 26.5
February 109 26.3 26.7 25.9 32.6 22.1
October 193 30.5 30.9 30.1 38.1 24.2
July 181 32.8 33.1 32.5 37.2 27.8
February 15 21.5 31.2 11.8 63 0
October 16 22.1 32.3 12.3 73 0
July 16 24.2 37.5 10.9 100 0
N TOTAL (mm)
February 15 5
July 16 36
October 16 83

Table 5. Seasonal changes in regulating phase body temperature in
the field and in the laboratory thermal gradient. Only
periods when the sun was not obscured by clouds were
included in the field calculations. Only third and fourth
day monitoring records were used in the calculation of mean
Tb's for gradient lizards. Values were taken from the Tb
records at 15 minute intervals. All lizards were non-



February 13 0/2 II 280 38.0 38.1 37.9 0.82 34.7 40.0

June 9 1/1 I 231 39.7 39.8 39.6 0.89 37.3 42.5

July 13 0/2 II 365 38.1 38.2 38.0 1.24 33.7 40.7

October 13 9/3 II 268 38.5 38.7 38.3 1.25 34.5 41.0


July-Aug 8 2/2 222 36.9 37.1 36.7 1.86 31.6 41.8

December-Jan 8 2/2 174 37.1 37.3 36.9 1.08 34.0 39.3

difference between June and July Tb means was probably due to the

difference in the amount of vegetation at Sites I and II. The variance

of mean Tb in February was significantly lower (p < 0.01) than in July

and October. The winter variance was lower primarily in the upper

portion of the Tb range (Figure 10). Lizards had been acclimatized to

the more thermally variable Gainesville climate before testing in the

thermal gradient (Table 5). Yet, summer and winter sample Tb means did

not differ significantly on any of the first four days in the gradient.

As in the Caicos, the variance of the mean Tb for winter animals was

significantly less than for summer animals (p < 0.01) and the lower

winter variance was more evident at high Tb (Figure 10). Thus,

acclimatization to low environmental temperatures in Cyclura appears to

involve an increased avoidance of high and low regulating phase Tb's

without change in mean Tb.

Mean Tb was significantly lower for CycZura monitored in the

gradient than in the field (Table 5). The July-August gradient mean was

2.8 C lower than the June field mean and 1.2 C lower than the July field

mean. The difference was only 0.9 C for the winter field and gradient

samples. In Figure 11 mean field Tb's of active lizards have been

plotted against mean gradient Tb's for lizard species from several

different families. Mean gradient Tb's are nearly always lower than

mean field Tb's above a mean field Tb of 37 C. Allowing Tb to rise

above the preferred gradient Tb is probably adaptive in diurnal helio-

therms temporarily living in hot environments, such as CycZura in

summer, since morning and afternoon activity periods are thus lengthened

(DeWitt 1967, Licht et at. 1966).










/ \

'I.- -

32.2 33.2 34.2 35.2 36.2 37.2 38.2 39.2 40.2 41.2 42.2

Figure 10.

Seasonal change in Cyclura regulating phase body temperature in
the Caicos and Gainesville, Florida. The February and July field
distributions and the October field distributions are for two and
three nonhyperthermic free-ranging male lizards,respectively.
Each month's field sample consisted of a total of 13 monitoring
days. The two thermal gradient distributions consisted of third
and fourth day results for two males and two females.



0 5






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-- I

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I i I I I | I 1

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There are at least three other reasons why lizards commonly have

higher field Tb's than gradient Tb's. First, Regal (1971) found that a

dominant Klauberiina riversiana provided with a subdominant lizard in the

same gradient box maintained a higher Tb than the same dominant lizard

monitored separately. Since gradient lizards are usually tested singly,

T.,'s may be lower due to missing social interaction present in the field.

Secondly, field Tb's measured by mercury thermometer rather than

telemetry, as was the case for practically all the points in Figure 11,

may be biased to those lizards in full sun and plain view as opposed

to sequestered individuals in deeply shaded surface areas (McGinnis and

Dickson 1967). Thirdly, lizards are commonly not fed while in the

thermal gradient, although reptiles often have elevated active temperatures

after feeding: lizards (Cogger 1974), snakes (Regal 1966), and turtles

(Gatten 1974c).

The single anguid plotted in Figure 11, Gerrhonotus multicarinatus,

which has such a low field temperature mean compared to its gradient

mean, is probably forced to be eurythermal due to its habitat choice.

It is a secretive, ground dwelling lizard living amongst shaded vegetation.

The lizard does occasionally bask, reaching a voluntary maximum of

approximately 35.7 C, considerably higher than the mean for active

lizards (Cunningham 1966). The field Tb's for the five gekkonids in

the figure were measured while the animals were in their diurnal retreats.

Even though their Tb's during nocturnal activity must necessarily conform

to air and substrate temperatures, gekkonids in their diurnal retreats

commonly seek out Tb's as high or higher than their preferred gradient

Tb's. The high diurnal Tb's may be necessary for digestion of food

collected during the night (Bustard 1970, Pianka and Pianka 1976).





22 24 26 28 30 32 34

36 38 40

Figure 11.

Relationship of mean body temperatures in the field and the
thermal gradient for active lizards from several families.
Solid triangles represent agamids, open triangle,anguid; open
squares; gekkonids; solid circles, iguanids;circles enclosing
dots,Cyclura at Site I in June and Site II in July vs. the
summer gradient mean and at Site II in February vs. the winter
gradient mean; open circles, scincids. Data were taken from
several sources: Bradshaw and Main 1966,Brattstrom 1965, Cowles
and Bogert 1944,Cunningham 1966, DeWitt 1967, Fitch 1954,
FitzpatricketaL 1978, Grenot 1976, Heatwole 1976, Huey 1974,
Lee and Badham 1963, Licht and Basu 1961, Licht etal. 1966,
McGinnis and Brown 1966,Norris 1953,Parker and Pianka 1974,
Pentecost 1974, Pianka 1971, Pianka and Parker 1972, Pianka and
Pianka 1976, Spellerberg 1972b, Vance 1973, Wilhoft 1958,
Wilhoft and Anderson 1960.



o o AA


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Egg laying was delayed in the Gainesville pen. A female captured

on April 4 laid in Gainesville on June 12, within the normal Caicos

nesting season of the first two weeks in June. However, another female,

which had been captive in Gainesville since July 30, 1974, laid in the

pen on July 25, 1975. Yet another female, captive since February 25,

1976, laid on July 25. The rate of egg development may have been slower

in Gainesville's cooler climate or shorter photoperiod (Mayhew 1961).

However, the delays may also have been partially due to a lack of nesting

burrows in the pen, resulting in egg retention. For example, a caged

female on Water Cay, captured on June 5, did not lay until June 17.

Habitat Complexity

A foraging Cyclura carinata, a semiarboreal lizard sometimes

traveling up to 1600 ft (488 m) a day, should receive a radiant heat

input from direct and filtered sunlight that is inversely proportional

to the density and height of the plants in its territory. If the habitat

niche of the species is sufficiently broad, the regulating phase Tb of

individual lizards should increase significantly as vegetational cover

decreases. This has been demonstrated for the eurythermal lizard, Anotis

aculatus (Ruibal and Philobosian 1970). Cyclura burrows were absent

from both beach and swales, infrequent in Mixed Woodland, perhaps due

to low food plant diversity, and infrequent in Mesic Coppice, perhaps

due to insufficient open areas for basking. Iguanas once lived in all

the other vegetation zones on Pine and Water Cays, reaching the highest

density in Rocky Coppice. This generalist habitat niche is not surpris-

ing considering the lack of significant vertebrate competitors.

Monitoring sites were carefully chosen in order to find the maximum

mean Tb difference due to differences in vegetational cover. The highest

regulating phase Tb's were expected in the sparsely vegetated Open Scrub

nearest the beach. However, man and his dogs had nearly extirpated the

lizards from this zone by the time my study commenced. Therefore, Site I

had to be located further inland in semi-Open Scrub bordering the Dense

Scrub. Lizard Tb's were expected to be lowest at Site II, a thickly

vegetated area covered with a mixture of Dense Scrub and Rocky Coppice,

bordering a rocky coast. The site was crisscrossed by a network of

bulldozed roads. On the average, bushes and trees were 63 percent taller

at Site II than at Site I (Table 6). Site II also had approximately 82

percent more shade, when roads were excluded from the transects.

As expected, mean 'T was significantly higher at Site I, although

the difference was not very great (mean difference = 1.6 C, Table 5).

The small lizard sample sizes were compensated for somewhat by the long

monitoring times. Inland environmental temperature and wind velocity

differences between sites were negligible. Thus, the Tb difference

was probably due to the vegetational cover difference. The site

difference was significant in hyperthermic as well as nonhyperthermic

lizards (Figure 12). The mean Tb difference was slightly less for

maximally hyperthermic than for nonhyperthermic lizards. The high

Tb distributions were negatively skewed while the low Tb distributions

were more normally distributed.

Caged lizards were monitored in an attempt to produce a significant

difference in mean Tb by varying the amount and kind of shade available

in the lizard's habitat. It was hypothesized that, given only two

burrows as heat sinks, each with relatively constant air and substrate

Figure 12.

Influence of habitat on body temperature. Each upper
frequency distribution is for three days of monitoring
of a maximally hyperthermic adult male Cyclura carinata
(Site I, solid line; Site II, dashed line). The lower
distributions are for the same two lizards cn the three
days of lowest mean Tb, unaffected by long periods of
overcast. Horizontal lines are ranges, vertical lines
are mean Tb's, and rectangles are plus and minus two
standard errors of the mean.




/ N
/ N
* S S S I





342 35.2 36.2 37.2 38.2 39.2 40.2 41.2 422 43.244.2


"""""' """""


Table 6. Vegetational cover at Sites I and II on Water
Cay. The height of a bush or tree was
measured at approximately 7.5 m intervals along
the transects, which were 30 m long.






2 SE






2 SE












temperatures below the lizard's minimum regulating phase Tb, mean Tb

and the standard deviation of mean T would be greater than for the

same lizard given vegetational shade, two burrows, and branches,

which allowed greater convective cooling of lizards perched off the

ground. Overall, mean Tb was significantly higher in the complex

habitat (p < 0.01), but individually, this was true only for Lizard 5

(Table 7). The results may have been opposite to those expected

because of lizard hyperthermia. Lizards 5-7 had their hyperthermic

peaks while in the complex habitat, perhaps overriding the effect of

the vegetational shade and the branches. The standard deviations of

overall mean Tb in the two habitats were about the same, again contrary

to expectation. The mean Tb of the four lizards caged in the complex

habitat did not differ significantly from the two free-ranging lizards

also monitored at Site I in June (Table 5). Clearly, caged Cyclura

required only a very simple habitat to thermoregulate as well as free-

ranging lizards.

Cloud Cover

Mean regulating phase Tb decreased linearly as overcast time

increased (Figure 13). The correlation coefficient was significantly

less than zero (p < 0.0001 for r = -0.042, X T = -0.042 Percent Cloud

Cover + 39.582). As expected, the correlation coefficient increased as

the weather got colder (June-July, r = -0.193, N.S.; Oct, r = -0.344,

N.S.; February, r = -0.541, p < 0.01). Mean Tb per day was never

depressed below 36.5 C by cloud cover times of less than 30 percent

of total time. Continuous overcast periods had to be fairly lengthy

to depress mean Tb below the mean minimum T for clear weather, since

Table 7. Body temperature of Cyclura carinata confined to cages
with two structurally different habitats. Lizards were
first monitored in the complex habitat for three to
four days, then in the simple habitat for two to five


4 3 60 39.9 1.17 0.30 2 48 40.4 1.40 0.40

5 4 101 41.1 0.85 0.17 3 95 39.6 0.87 0.18

6 3 64 38.1 1.10 0.28 5 97 37.7 1.54 0.31

7 4 104 38.8 3.54 0.69 3 90 38.2 1.15 0.24

Overall 14 329 39.7 1.63 0.18 13 330 38.8 1.60 0.18

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large adult CycZura cooled slowly and radiative heat input continued

during light overcast. The high mean Tb of 42.3 C during June, achieved

with an overcast time of 54 percent, was possible due to the thinness of

the cloud cover.

Lizard Tb sometimes increased rather than decreased during over-

cast periods, especially when the overcast lasted only a short time

(Figure 14). When the lizard had been heating prior to the overcast,

the post overcast Tb rise can be explained as a result of thermal lag.

However, Tb also commonly rose initially during overcast after decreasing

before overcast, the maximum Tb during overcast being higher than the

previous maximum before overcast. Iguanas sought out hot substrates

avoided while the sun was shining and assumed a prostrate posture

(Figure 44, Illustrations 4 and 11). It appears that higher core Tb

was tolerated under these conditions, since overheating, as indicated

by body surface temperature, was not possible. The noises of lizard

activity; that is, walking, chasing, arboreal feeding, and dropping to

the ground after feeding, nearly ceased during extended overcast periods.

Except for short walks, iguanas remained practically motionless until a

few minutes after an extended overcast cleared. The abruptness of the

activity cessation varied directly with the severity and duration of

the overcast. Short periods of overcast, frequently encountered,

resulted in little or no curtailment of activity. The Tb change during

overcast differed slightly with season. On the average, Tb decreased

2.0 C per hour during February, 1.3 C during June-July, and 2.6 C

during October, the month of heaviest overcast. A large increase in

Tb was most likely during summer overcast.

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Shaded Air Temperature

In Huey and Slatkin's cost-benefit model for thermoregulation

(1976), the value k represents a lizard's "thermoregulatory strategy,"

varying from perfect thermoregulation (k = 0) to passive nonregulation

(k = 1). The linear regression coefficient r for a graph of Tb vs.

shaded T at the lizard's body surface is a good estimate of k. A lizard

living in a tropical forest would be expected to have a high r value,

since direct solar radiation near the forest floor is only patchily

available. On the other hand, regulating phase Tb should be practically

independent of shaded T in a heliothermic lizard like Cyclura, living

in fairly open habitats. CycZulra, with its low r values, is a nearly

perfect thermoregulator (Figure 15; r = 0.151 in Graph 1, 0.013 in

Graph 2, 0.131 in Graph 3, and 0.154 in Graph 4).

Mean Tb-Ta during the regulating phase at Site II was least in

July (X = 5.9 C, SD = 2.00, Range = 1.2-10.4 C, N = 68), greater in

October (X = 7.2 C, SD = 1.65, Range = 4.2-12.2 C, N = 67), and greatest

in February (X = 11.0 C, SD = 2.11, Range = 5.5-15.6 C, N = 58), since

shaded air temperature decreased faster seasonally than Tb, again

expected in a heliotherm.

One problem with this analysis is that the air temperature was not

measured at the surface of the lizard, but rather at a site near the

blind. An attempt was made to select the lowest shaded air temperature

at the site. The assumption was made that this air temperature was also

available to the lizard. If this assumption is correct, the value of r

is still a measure of the degree of heliothermy. Of course, the

correlation of any instantaneous thermal input with core Tb declines as

body size increases in a lizard moving rapidly through a varied thermal


30 34 38 22 26 30

Figure 15.

Correlation of lizard body temperature during the regulating
phase with shaded air temperature. Each graph represents the
data for one dominant male (Graph 1, Lizard 3; Graph 2, Lizard 9;
Graph 3, Lizard 11; Graph 4, Lizard 3). Tb was independent of
shaded air temperature in all four lizards. Data were collected
on five to seven clear days in February (Site II), June (Site
I), July (Site II), and October (Site II), respectively.




I i I l I I I I

! i t | I |

Substrate Temperature

Heliothermic lizards are able to behaviorally maintain body tempera-

ture within narrow limits, somewhat independently of ground surface

temperatures, which fluctuated with changes in daily and seasonal

thermal flux, cloud cover, and wind speed. McGinnis (1970) coined the

term "thermoregulatory flexibility" for this ability of heliothermic

lizards. Even during the hottest days, shaded substrates other than in

burrows were available at temperatures well below lizard Tb (Figure 16).

Iguanas rested quietly in the shade during maximum midday insolation

rather than retreating to a burrow, in a posture somewhere between

prostrate and upright (see Figure 44). Tb was usually considerably

less than the sand surface temperature in the sun (T sn) on clear
days, except during the early morning and late afternoon (upper and

middle graphs). Hyperthermic lizards in June decreased the T ss-T
ssn b
difference more than February nonhyperthermic lizards by spending con-

siderable time in exposed areas. Iguanas remained above ground during

mildly heavy overcast on partly cloudy days, receiving maximum insol-

ative heat input with minimum convective heat loss by sitting in exposed

areas protected from the wind. T. was commonly higher than T under
D ssn
these conditions (lower graph). Nonetheless, Tb eventually decreased

during extended overcast. Tb decreased more slowly than Tssn in the

late afternoon on clear days due to the longer heat retention time of

the lizard's body than the surface of the windswept sand. The negative

T ss-Tb difference in the late afternoon was not as great as shown in

the middle graph, however. Large males, the last lizards to submerge,

sought out the last remaining sunspots in the habitat, unavailable to

me for temperature measurements without disturbing the lizards. Also,

Figure 16.

Thermoregulatory flexibility. Tb's of emergent lizards
have been subtracted from the sand surface temperature in
the shade (solid circles, Tssh Tb) and from the surface
temperature of sand continually exposed to the sun (open
circles, Tssn Tb). Solid and dashed lines encompass the
Tssh Tb and Tssn Tb values, respectively. Solid and
dashed lines also indicate the hourly mean values (upper
two graphs only). Data for the upper, middle, and lower
graphs were collected on 14 clear days in February at
Site II, 8 clear days in June at Site I (lizards hyper-
thermic), and 5 partly cloudy days in June at Site I,
respectively. Mean Tssh, Tb, and Tssn values are given
on the left side of each graph.




37.2= XTb

26.6 =Ts sh


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iguanas kept their ventral body surfaces in contact with the substrate

during this period. The sand surface temperature important in con-

ductive heat exchange, lying beneath the motionless lizard's body, did

not decrease as rapidly as T

Patterns of Heat Transfer between Penned Iguanas and
their Environment: The Three-Transmitter Study

Heat transfer occurs everywhere on the lizard's body surface.

Dorsal heat exchanges are primarily radiative and convective while ventral

exchanges are also conductive. Heat loss due to evaporation of water from

cutaneous and respiratory surfaces and heat gain due to metabolism and

condensation of water vapor will be assumed to be approximately equal

in the following analyses and thus, ignored. Based on temperature

received from the dorsal surface, gut, and ventral surface transmitters,

four heat transfer conditions were possible: 1. The lizard simultaneously

received a net heat input from both dorsal and ventral body surfaces,

that is, both the dorsal and ventral transmitter temperatures were

higher than the gut temperature, 2. the lizard received heat dorsally

and lost it ventrally, 3. lost heat dorsally and gained it ventrally,

and 4. lost heat both dorsally and ventrally. All four heat transfer

conditions usually occurred sometime during an emergent lizard's day,

as illustrated in Figure 17 for a large male.

Three problems concerning the limitations of the transmitter

technique should be pointed out. Ideally, the time constant for

transmitter sensing of a rapid temperature change in the environment

should be infinitely small. However, this was not the case. For

example, the lizard in Figure 17 moved to the shade at 1109, resulting

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in a rapid change from Condition 2 to Condition 4. When the transition

time was taken from the temperature records, however, Condition 4 did

not start until 1112. The second problem was the small number of

transmitter monitoring sites. Large heat exchange differences often

occurred at different locations on the lizard's body surface. For

example, the anterior portion of the lizard was often in the shade

while the dorsal black body probe was in the sun. Also, fairly large

internal temperature differences occurred, as between the head and the

gut. It is undoubtedly technically feasible to double or triple the

number of temperature monitoring sites on a free-ranging lizard the

size of an adult male Cyclura. Thirdly, the surface probes should

have been implanted subcutaneously, since temperatures there were

probably of greater biological significance. The temperature difference

was probably minimal between the subcutaneous area and the ventral

surface as measured. However, dorsal black body temperature probably

differed somewhat from the dorsal skin surface temperature. Hopefully,

since the thermal lag time of the transmitter probe was less than the

subcutaneous area, the calculated times for the heat transfer con-

ditions were not grossly inaccurate.

Several patterns of heat transfer were consistently observed during

the morning heating and regulating phase. Only Conditions 1 and 2

occurred during the morning heating phase on clear days. Typically,

lizards emerged from the plywood shelters and, after a short delay,

walked to a sunlit patch in the still partially shaded pen, where sand

surface temperature exceeded gut temperature. The resulting Condition

1 lasted a variable portion of the morning heating phase, depending on

whether, how soon, and how many times the animal moved to another sunlit

area. Condition 4 typically alternated with Condition 2 during the

early regulating phase, when lizards shuttled at a high rate. As

substrate temperatures rose and lizards tolerated these higher tempera-

tures, Conditions 3 and 1 became more common. Lizards probably

tolerated higher body surface temperatures than core temperatures,

as evidenced by the mean maximum temperature of the dorsal black body

transmitter (X = 45.8 C, SD = 2.0, Range = 40.6-50.0) exceeding the

mean maximum of the gut (X = 38.3 C, SD = 1.0, Range = 36.1-39.7).

However, the mean maximum black body temperature did not exceed the

critical thermal maximum of the core (X = 46.2 C). Lizards commonly

returned to the plywood shelters for lengthy periods during midday hours,

where nearly stable body temperatures were eventually temporarily

attained (Figure 17). Lizards usually avoided the shaded sand avail-

able underneath the shelters during this time in favor of the higher

temperatures in the shelters. The same shade choice selectivity with

resultant Tb stabilization was observed in the field. Condition 4

predominated when the pen became shaded in the afternoon, since lizard

surface temperatures declined faster than gut temperature. By seeking

out relatively warm, recently shaded substrates and assuming a

prostrate posture, lizards temporarily stopped their core temperature

decline (Figure 17, 1630-1642). They were not usually thigmothermic

during this time, however, since ventral surface temperature did not

usually rise above core temperature.

The most common heat transfer condition was Number 2, occurring

an average of 51.3 percent of the morning heating plus regulating phases

(Figure 18, left graph). Condition 3 occurred only 2.5 percent of the


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