% OBSERVATIONS 
Lizard Ethology 
217 
TIME 
Figure 12. The proportions of the kinds of activi- 
ties observed within the shelter for subjects A 
(female), B (subordinate male), and C (dominant 
male). The dark portion of each bar = sleeping 
or quiescent animals; the hatched portion = 
animals are active on or between shelves; the 
striped portion = time spent surveying the 
habitat from within the shelter (“covert perch- 
ing”). 
These observations make it clear that, in 
an experimental design concerned with 
activity levels, one must also consider activ- 
ity that may occur in microhabitats normally 
concealed from the observer. 
Social Behavior 
In his study of Anolis nebulosus ethoecol- 
ogy, Jenssen (1970a.) used crowded conditions 
to “catalyze” social interactions. He was 
confident that the motor patterns exhibited 
under these conditions were essentially the 
same as those seen in nature, although the 
frequency of displays was probably abnor- 
mal. 
The behavioral or perceptual space of a 
laboratory habitat can affect some lizards in 
unexpected ways. In some cases small en- 
closures in which lizards are continually 
exposed to one another will diminish inter- 
actions. Mayhew (1963a.) observed that a 
large and a small Amphibolorus pictus co- 
habited peacefully in a small enclosure, but 
when both were transferred to a larger 
vivarium, the large male vigorously pursued 
the smaller animal. Mayhew proposed that 
the small enclosure inhibited the normal ex- 
pression of territoriality. 
I have observed the same phenomenon in 
a colony of Agama agamas. Harris (1964) 
observed that some Agama males are “re- 
pressed” by the presence of a dominant male, 
made conspicuous by its bright red head. 
Perhaps such a “repression” exists in small 
laboratory habitats where lizards are con- 
tinually exposed to dominants. Repression 
may then abate under less restrictive condi- 
tions in which the smaller lizard may devel- 
op territorial habits that elicit aggressive 
responses in the dominant. 
In nature, environmental influences on 
aggression in lizard populations are not un- 
common. Many lizards that are mutually 
intolerant under normal conditions will 
aggregate during adverse weather or at 
night (Evans, 1967, in Coleonyx; Curry- 
Lindahl, 1957, in Agama cyanog aster; and 
Regal, 1968; in Klauberina) , or at sites hav- 
