210 
Greenberg 
Figure 5. Closed-circuit television closeup. The CCTV system has a timebase generator to record the date 
and time to one hundreths of a second on each frame. 
of blue spiny lizards (1973a), individuals 
maintained in a large habitat (Fig. 2) spon- 
taneously resumed a seasonal pattern of 
social activity after more than a year under 
constant conditions. Those in much smaller 
habitats did not. 
Dim light is of little thermal significance, 
but simulated twilight transitions have been 
shown to have a potent effect in normalizing 
the activity patterns of animals in the labo- 
ratory (Kavanau, 1962, with mice; Regal, 
1967, with lizards). Dim light may cue a 
lizard’s shelter seeking so that it will not be 
caught far from its shelter when night falls 
(Regal, 1967). In the morning, some lizards 
may be cued by light to emerge (Greenberg, 
1976a), while others apparently rely on the 
penetration of morning warmth into their 
shelters (McGinnis and Falkenstein, 1971; 
Bradshaw and Main, 1968). 
An endogenous circadian rhythm was 
posited by Heath (1962) to account for the 
emergence of Phrynosoma in apparent “anti- 
cipation” of the onset of laboratory heat- 
lamps, but McGinnis (1965) has argued that 
such a rhythm could be an artifact of the 
consistency of the laboratory habitat. 
The importance of ultraviolet light for 
some species is apparent both with respect 
to metabolic needs (Reichenbach-Klinke and 
Elkan, 1965) and the expression of normal 
behavior (Moehn, 1974). Licht (1973) has 
