Ritualistic Behavior Lizards 
257 
monster (Heloderma siLspectum) inflates its 
body, lo-wers its head, and thrusts or butts at 
its adversary. 
The marine iguana {Amblyrhynchus 
cristatus) of the Galapagos Islands charac- 
teristically attempts to drive off another male 
encroaching on its territory by attacking 
with lowered head which is crowned with 
large conical scales. The adversary counters 
with the head directed in a like manner (Fig. 
5). The result is a head-butting contest. The 
significance of this performance has been 
demonstrated experimentally by holding a 
male in the territory of another male and 
observing the attack and counter reactions. 
A male has been observed to butt the severed 
head and shoulders of another male from its 
territory. Females of this species also exhibit 
head butting in defense of nest burrows on 
the nesting beaches (Carpenter, 1966). 
The little anole from western Mexico, 
Anolis nebulosus, when threatening another, 
may initially stand on its hind legs while 
extending the dewlap. The other male often 
responds in the same manner (Jenssen, 
1970). This behavior appears only under 
high intensity aggression and at the start 
of displaying. 
Color change may serve to enhance the 
intimidating appearance of an aggressive 
male. This is most highly developed in certain 
agamid lizards and in the Chameleontidae. 
Color change in the dominance-subordinate 
social context is most pronounced in the 
rainbow lizard (Agama agama agama) of 
Ghana. A subordinate male is light brown in 
color, but, with changes in dominance, may 
show gradations of a very contrasting color 
pattern of orange head, cyanine blue legs 
and trunk, and banded orange and blue tail 
(Harris, 1964). The small agamid from 
North Africa {Agama savignyi) demon- 
strates only partial color changes. When this 
lizard is subordinate or in a nonsocial con- 
text, its throat region is much the same color 
of light brown as the rest of the body. When 
the animal is dominant, the throat becomes 
a deep blue color and develops a pouch-like 
dewlap that contrasts greatly with the rest 
of the body (Fig. 6). 
Territoriality 
Central to the development of aggressive 
behaviors in the iguanids and agamids is 
the defense of a territory (Carpenter, 1967). 
The territory and its defense are evidently 
related to the visual sense. This is suggested 
by the behavior of the marine iguana {Am- 
blyrhynchus cristatus). The male will defend 
the top surface of a large boulder on the reef 
or shore area, while another male — out of 
sight — may defend a territory below this 
boulder (Carpenter, 1966) (Fig. 7). Most 
iguanids and agamids display from elevated 
sites in their territories where they are most 
likely to be seen by their congeners. 
Display 
The greatest degree of ritualism, stereo- 
typy or rigidity of behavior appears in the 
display. Although my colleagues have shown 
there is geographical variation in these dis- 
play rituals, the basic pattern within most 
iguanid species appears to represent an 
evolved, genetically programed performance 
(Ferguson, 1971; Jenssen, 1971). 
The study of these aggressive displays 
has advanced considerably from the original 
time-motion studies using a stopwatch 
(Carpenter and Grubitz, 1961; Hunsaker, 
1962). It was apparent in my early studies 
that the display involved more than move- 
ment, and a series of categories was estab- 
lished for recording all elements of the dis- 
play: display site; position (orientation) on 
this site during an encounter; the postural 
changes that took place; and the types of 
movement and temporal sequences of the 
body movements (Carpenter, 1962). By using 
these categories, it was possible to compare 
the displays of various genera, species, sub- 
species, and populations. The use of motion 
pictures (at specific speeds) and single frame 
analysis projectors has greatly increased the 
accuracy of measurements of the time-motion 
elements of the display, providing more pre- 
cise quantification of which to base statistical 
analysis. 
