Learning in Lizards 
177 
darkened room with an ambient temperature 
of 22±3°C. A 250 w white-bulb infrared 
light provided a thermal gradient of 22 to 
55 °C. Eleven adult male Dipsosaurus dorsalis 
and six Sceloporus magister with a diverse 
previous thermal history were the subjects. 
The lizards were not fed for 2 to 3 days 
prior to experiments and were kept at room 
temperature without additional light or 
food for the 4 or 5 days of the experiment. 
On consecutive days, a single male lizard was 
placed in the thermal gradient for 1 hour 
only each day. Four to five lizards were run 
each day, but each individual was run at 
the same time in the day. Body temperatures 
were monitored continuously with YSI Tele- 
thermometers. The thermal gradient was 
monitored continuously to insure stability. 
Figure 1 presents the results of a typical 
lizard in the gradient on 5 successive days. 
Initially a lizard would run around the 
gradient, discover the heat source, heat up, 
and then proceed to engage in shuttle be- 
havior in order to maintain its preferred 
body temperature. On subsequent days, how- 
ever, (see Fig. 1 and Table 1), they became 
more precise in their thermoregulation. Ap- 
parently, they had learned to use the thermal 
mosaic of the gradient to reduce the time 
needed to warm up and maintain a pre- 
ferred body temperature. Table 1 presents 
data on mean variation in body temperature 
over the last 30 minutes (after initial heat- 
ing) during the lizard’s hour in the gradient 
on successive days. It is clear from these 
data that the variance is reduced (i.e., the 
lizard became more precise in its ability to 
behaviorally thermoregulate). The findings 
confirm those of DeWitt (1967a, b) and ad- 
ditionally show that the lizards can increase 
their thermoregulatory precision with only 
1 hour of experience in the gradient per day. 
Another interesting observation was that 
in the process, there was a change in mean 
body temperature with each day. Dipso- 
saurus, while reducing variance in mean body 
temperature, raised its preferred body tem- 
perature on each subsequent day (mean of 
1 minute readings over last 30 minutes). 
Sceloporus magister, on the contrary, low- 
ered its preferred body temperature on each 
subsequent day (Table I). Acclimation effects 
prior to the experiment may have resulted 
in these changes, but animals of both species 
were treated similarly. 
Figure 1. Precision of temperature regulation in 
lizards. Body temperatures of a single Dipsosaurus 
dorsalis monitored continuously when placed in a 
thermal gradient for one hour only a day. Data 
are for days 1, 3, and 5. 
TABLE 1 
Precision of behavioral thermoregulation in lizards. Mean variation in body temperatures 
(°C) of lizards for the last 30 minutes of an hour in a thermal gradient (see text). Dd.d- 
Dipsosaurus dorsalis, S.o.-Sceloporus magister. 
Species 
N 
Trial 
Remarks 
1 
2 
3 
4 
D.d. 
5 
4.4 
3.9 
1.2 
2.5 
with means rising from 39.5-40.0. 
D.d. 
4 
4.4 
4.5 
1.3 
.8 
with means rising from 37 to 43. 
S.o. 
5 
4.5 
2.2 
2.0 
1.8 
with means decreasing from 38.0 to 36.8. 
Average 
4.5 
3.4 
1.5 
1.7 
