176 
Brattstrom 
reward side of the box. Minimum and max- 
imum voluntary temperatures for these 
lizards in the field are 26.4° and 38.0 °C 
respectively (Brattstrom, 1965). Hence, their 
behavior in the resting box appeared to rep- 
resent one trial learning. As a further refine- 
ment, Harlow constructed a box in which 
only a small portion of the floor could drop 
and turn on a heat lamp, the light of which 
directed toward the treadle area. The experi- 
ment was conducted in a cold room (8°C). 
After wandering about the box and acci- 
dentally contacting the treadle and becoming 
warm, lizards would retreat to the cool areas 
of the box. After 1 to 10 minutes and a 
decrease in body temperature of 1 to 5°C, 
all lizards returned to the treadle (average 
body temperature leaving heat, 37°; leaving 
cold, 35°; mean body temperature of field 
animals, 35.0°C [Brattstrom, 1965]). Sub- 
sequently, shuttling behavior became more 
frequent and the range of body temperatures 
of the five tested animals was reduced (Har- 
low, personal communication). Thermoregu- 
lation had become more precise. 
A next step was to construct a bar- 
pressing apparatus for operant conditioning. 
The animals were placed in a galvanized 
screen cage with a 250 w infrared lamp 
that is turned on when a lizard presses a 
small bar with his head or limbs. The heat 
lamp turns off at any number of fixed time 
periods. The time periods are changed ac- 
cording to the species so that there can be 
adequate heat gain. Body temperature is 
monitored by means of a thermistor. In an 
initial study with five Dipsosaurus, Payne 
(personal communication) found that once 
the lizards encountered the bar, they would 
press the bar 1 to 17 times and raise their 
body temperatures from 30 to 34° to 38 °C. 
After 15 to 40 minutes, they would leave the 
bar and not return. Subsequently, Stevens 
placed Sceloponts occidentalis in this ap- 
paratus and observed repeated bar pressing 
with return to the bar after cooling (Stevens, 
in press). Richardson and Brown (1975 and 
MS) have obtained excellent results in simi- 
lar experiments with Dipsosaurus, although 
Crotaphytus collaris, the collared lizard is an 
even better subject (Richardson, personal 
communication) . 
LEARNING THE THERMAL MOSAIC 
OF THE ENVIRONMENT 
Diurnal basking lizards (largely Iguanids 
and Agamids) spend a considerable amount 
of time in behavioral thermoregulation 
(Cowles and Bogert, 1944; Brattstrom, 1965, 
1971 ; Health, 1965; and others). A minimum 
body temperature is required for a lizard to 
raise its metabolic rate to an efficient operat- 
ing level. Behavioral and physiological mech- 
anisms that allow a lizard to reduce basking 
time are advantageous in that they allow 
more time for other activities such as forag- 
ing, mating, and so forth. Efficient use of the 
thermal mosaic of the environment is one of 
the several ways lizards can reduce basking 
time (Brattstrom, 1965; Heath, 1965; and 
Templeton, 1971). Heath (1962) showed in 
the laboratory that morning emergence of 
horned lizards, Phrynosoma, was due to their 
biological clock, and that lizards that 
emerged prior to the turning on of heatlamps 
would go to patches of ground that were first 
struck by the light of the lamp. 
DeWitt (1967a) carried out a series of ex- 
periments in a circular thermal gradient with 
Dipsosaurus dorsalis to show that this species 
becomes more precise in its behavioral regu- 
lation of body temperatures with more ex- 
perience in the gradient. 
For many species, laboratory-determined 
preferred body temperatures are character- 
istically lower (or higher) than field deter- 
mined mean body temperatures. McGinnis 
and Dickson (1967) and DeWitt (19676) 
brought the problem of the differences be- 
tween behavioral thermoregulation in the 
field and the laboratory into question. Does 
the preferred body temperature of lizards 
determined in a thermal gradient relate to 
the mean body temperature in the field? 
My approach to the problem was as fol- 
lows: An elongated photothermal gradient, 
10 X 2 X 3 ft., was constructed of wood and 
filled with four inches of sand and kept in a 
