Lizard Ethology 
219 
“challenge” display (Gorman, 1968) and the 
lower intensity “fanbob” that they observed. 
In my observations of blue spiny lizards, 
a discontinuity of display “motivation” was 
suggested by the finding that assertive dis- 
plays varied greatly in intensity and were 
often performed with much more vigor than 
many challenge displays. 
An analysis of the conditions in which 
assertive displays occur suggests that the 
only thing that they all have in common is a 
clearly elevated level of arousal — at least in 
terms of sensitivity to peripheral stimuli 
(Table 2). 
The appearance of an assertive display 
during foraging illustrates the importance 
of the experimental habitat for the eliciting 
and subsequent functional interpretation of 
social displays. 
SOCIAL CLUES ABOUT THE CAUSATION 
OF BEHAVIOR 
Manning (1967) regards the species dif- 
ferences in the head-bobbing patterns of 
Sceloporus described by Hunsaker (1962) 
as an elegant example of gene control of 
changes affecting thresholds within the 
nervous system. An analysis of display be- 
havior may be of value in suggesting 
hypotheses about the neurophysiology of 
displays if sufficient information about dif- 
ferent species is obtained to suggest how 
displays have evolved. 
Display is often the most dramatic be- 
havioral pattern with which ethologists deal. 
It is probably at the end of a continuum of 
homologous behavioral patterns that begins 
with less striking behavior, such as loco- 
motor intention movements (Daanje, 1950) 
or somatic or autonomic responses (Morris, 
1956). We may ask with Barlow (1968:227) 
— do shared effectors mean shared central 
nervous system mechanisms? If we think 
that they might, ideas about the different 
functions of homologous behavioral patterns 
might yield important clues about the neural 
aspects of ritualized behavior. 
Consider the head nodding of an iguanid in 
terms of conflicting components of autonomic 
stimulation. I have observed an exchange of 
signals in blue spiny lizards (Greenberg, 
1973a, 1977a) that suggests that the nod 
may represent an alternating pattern of fear 
and aggression : Every time a dominant 
Table 2: The contexts in which the “assertive” display of the blue spiny lizard is observed. About 76 percent 
of the display were in nonsocial contexts. 
Female 
Male 
% of Total 
Assertive 
Displays 
(n) 
NON-SOCIAL 
SPONTANEOUS 
100. 
00.0 
09.0 
(7) 
AFTER MOVEMENT 
DURING FORAGING 
52.6 
47.4 
25.3 
(19) 
AFTER ATTAINING 
PERCH 
14.8 
85.2 
36.0 
(27) 
DURING EMERGENCE 
00.0 
100. 
02.6 
(2) 
SOCIAL 
RESPONSE TO ACTION 
OR APPEARANCE OF 
ANOTHER LIZARD 
80.0 
20.0 
20.0 
(16) 
IMMEDIATELY AFTER 
SOCIAL INTERACTION 
00.0 
100. 
06.7 
(6) 
