232 
Ferguson & Bohlen 
to 1900 hours. After removal of a clipboard, 
the insects trapped on it were identified to 
Order, classified according to length and 
width and counted. 
Observations indicated that ants avoided 
the clipboard traps. Because ants were 
suspected to be important food sources, their 
density was assessed by enclosing a 10 cm^ 
area with a wire square and counting the 
number of them entering the area in a given 
period of time. There were four “insect 
census days” a month from June 1 to August 
11. As a further means of assessing dietary 
habits, a sample of 5 to 10 lizards was 
periodically removed from the habitat ad- 
jacent to the study area and the contents of 
their stomachs examined. 
The social behavior of juvenile lizards pre- 
viously marked on this study area was ob- 
served for 26 fifteen-minute periods from 
August 8 to September 15, 1972. Periods of 
observation were concentrated in midmorn- 
ing and early afternoon. The number of 
social encounters, individual lizards involved 
in each encounter, and the nature of each 
encounter were recorded on audio tape and 
later transcribed to summary sheets. After 
the final observation period, each lizard was 
recaptured and remeasured. Lizards were 
recaptured again between these dates only 
if their paint mark was lost. 
Finally, crowding tolerance tests were con- 
ducted on juvenile prairie swifts hatched 
from eggs laid by females from Reno County, 
Kansas. A complete description of the tech- 
nique is given in Tubbs and Ferguson (1976). 
Briefly, eggs were harvested in outdoor en- 
closures and incubated in small jars. The 
hatchlings were measured, weighed, marked 
by toe clipping, and introduced either singly 
or in groups of 5 to 10 into 2 x 5-feet metal 
enclosures. The metal sides of the tanks 
prevented escape of the lizards and 2-inch 
wire mesh covering the top prevented the 
entry of bird predators. The behavior of the 
juveniles in isolated and group environments 
was observed each day, and growth and sur- 
vival rates were recorded. Care was taken in 
each case to make the crowded and group 
environments as similar as possible in regard 
to sun exposure, substrate temperature, food 
availability per lizard, cage accessories, sub- 
strate type, and natural plant growth within 
the enclosures. Thus, the major difference 
between the environments of lizards during 
experiment was social density. Two experi- 
ments were conducted : one early in the hatch- 
ing season with early clutch hatchlings (July 
24 to August 18, 1972), and the other later in 
the season with late clutch hatchlings (Au- 
gust 8 to October 10, 1970; and August 31 
to October 19, 1971). The design and sched- 
ules of the experiments are given in Table 2. 
Lizards were fed “standard net sweeps” of 
insects according to the schedule in Table 2. 
A “standard net sweep” was obtained by 
driving a car through a grassy field at 20 
m.p.h. with the insect net out of the window 
and dragged in the grass for approximately 
1 minute. Large insects and spiders which 
could potentially harm lizards were removed. 
Catches from net sweeps were introduced 
just after behavioral observation periods. 
The “standard net sweep” feeding schedule 
seemed to provide sufficient food. Although 
the number of palatable insects available to 
each lizard was not assessed quantitatively 
for a “standard net sweep,” small insects 
such as small black ants and lepidopteran 
larvae (known from stomach analysis to be 
eaten by this species in the field in Kansas, 
Table 6) were often eaten during the obser- 
vation periods just prior to an introduction 
of net sweep catches. 
RESULTS AND DISCUSSION 
Aggression in the Field 
During the 26 observation periods, 12 
natural encounters were observed (Table 3). 
Eleven encounters were between two juve- 
niles of different sizes, while one involved an 
encounter between a juvenile and an adult. 
All encounters resulted in an aggressive 
interaction of varying intensity, and in all 
interactions the larger lizard was clearly 
dominant, i.e., caused the other lizard to 
