Table 12. — Frequency of capture of males and females 
Males 
Females 
A. From burrows or harborage boxes 
396 
361 
B. Captures and recaptures in traps 
387 
265 
C. Initial repeats 
133 (0.34 of B) 
62 (0.23 of B) 
D. 2d, 3d, etc., repeats during same trapping period 
46 (0.35 of C) 
21 (0.34) of C) 
A with B comparison: Chi Square=6.76; p=.01. 
B with»C comparison: Chi Square=4.59; p=.02. 
C with D comparison: Chi Square=0.007; p=.95. 
old of modification of behavior is reached, males 
and females respond similarly. This is discussed 
in more detail in the section, “Social Stress and the 
Proneness to Enter Traps”, pages 95 to 99. 
F. Variability of the Trap- Avoidance Behavior. Pre- 
vious analysis suggest that some rats enter traps 
more frequently than others. In order to investi- 
gate this variability further, an index of the positive 
aspect of the behavior, i.e., proneness to enter traps 
was developed: 
Trap-proneness index = Number of times cap- 
tured/number of pe- 
riods rat was exposed 
to being trapped. 
This index varied from 0.0 to 2.0. A rat which 
never entered traps has an index of 0.0. One which 
enters once during each period of exposure has an 
index of 1.0. One which repeats occasionally, in 
addition to captures and recaptures may have an 
index over 1 .0. 
This trap-proneness index was determined for all 
rats which were bom in the pen and who lived for 
at least 277 days (fig. 77). Seventy-three males and 
64 females were included in this restriction of the 
population. It will be noted that for both sexes 
the distribution of this behavior approaches a nor- 
mal one. This was the only behavior for which a 
quantitative analysis was possible with reference to 
its variability. As discussed in the following sec- 
tion the major variability of this behavior is 
assumed to result from the social structuring of the 
population rather than from genetic variability. 
The degree to which rats enter or avoid traps has 
been discussed entirely upon the basis of their prior 
experience of having been confined in a trap. 
However, 38 percent of those rats which lived to 
277 days of age were not trapped on their first 
exposure to traps following initiation of above- 
ground activity at between 25 to 30 days of age 
(see table 13). Of these a few rats were not cap- 
tured until their third or fourth exposure to traps 
and three rats were never captured at all in traps’ 
although each was exposed to being trapped during 
four to seven different periods. It will be recalled 
that the traps when not being used were left in piles 
scattered about the pen. Therefore, they can 
hardly be considered as strange objects, other than 
that they occurred at new locations when set. In 
order to preclude this change from eliciting a 
strange object reaction it was the usual procedure 
to prebait the traps for 2 or 3 days with the doors 
off so as to accustom the rats to entering the traps. 
Because of the large number of traps set and their 
distribution through the entire pen, the lack of rats 
entering a trap cannot be attributed to the lack of 
opportunity of encountering set traps. Therefore, 
it is concluded that the avoidance of traps by rats 
which had no prior experience of being trapped is 
probably attributed to their behavior being influ- 
enced by the behavior of their older associates, 
which evidenced an avoidance behavior toward 
traps. If this interpretation is correct, it is impor- 
tant because it indicates the possibility of cultural 
determination of behaviors without the individual, 
having to experience the situation normally 
required to elicit the behavior. 
Table 13. — Period of exposure at first capture 
Trapping period 
Number 
of rats 
Mean age 
in days at 
capture 
Standard 
deviation 
First 
85 
48. 2 
14. 9 
Second 
40 
75. 6 
15. 8 
Third 
7 
118. 0 
33. 8 
2 
193.0 
*3 
*These 3 rats lived through a total of 15 trapping periods 
(4, 4, and 7 respectively) without ever being taken in traps. 
94 
