Lizard Ethology 
215 
Figure 10. Photo of CCTV frame of the legs-out component of the basking posture 
in Agama. 
some lizards. Juveniles, however, rarely show 
such reluctance and may in fact be the 
initiators of a feeding episode. 
Dietary supplements are often employed 
to compensate for the deficiencies inherent 
in diets of limited prey types. Of these sup- 
plements, calcium may be the most im- 
portant. Changes in activity may occur be- 
cause of inadvertaint dietary deficiencies. 
For example, there is an increase in activity 
observed in fowl deprived of calcium and 
sodium (Hughes and Wood-Gush, 1973). 
Use of Shelters 
The shelter appears to be more than a 
mere site of sequestered rest, a hiding place 
from potential predators or aggressive con- 
specifics, or protection from environmental 
extremes. The availability of shelter has been 
shown to have a function in the normal ex- 
pression of circadian thermal activity 
(Regal, 1968). At certain times, the crevice- 
dwelling blue spiny lizard will defend a 
crevice as a territory. Excluded individuals 
have been observed burying themselves in 
loose substrate (Greenberg, 1973a). 
Blue spiny lizards will occasionally bask 
inside their shelter, sometimes orienting to a 
thin shaft of light and at other times pres- 
sing their backs to a warm overlying rock 
shelf. Such “covert basking” is not uncom- 
mon; it has also been observed in Gehyra 
(Bustard, 1967), Dipsosaurus dorsalis 
(DeWitt, 1971), and even in the usually 
arboreal Anolis nebulosis (Jenssen, 1970a). 
Perching just inside the threshold of a 
shelter, alert for prey or social activity, was 
often observed. The pattern of shelter 
utilization seemed to refiect the social organi- 
zation of the population. Some lizards were 
consistently more exposed than others. 
These data indicated that observations of 
activity within a shelter would be of value. 
To make such observations of the blue spiny 
lizard, the “shelter column” enclosure was 
developed. This habitat was constructed to 
