Figure 78. — The frequency of intervals between recaptures. 
The frequencies are 3-point moving averages, except for 
the terminal points, which are the observed frequencies. 
Had every rat been trapped during each trapping period, 
the dotted "possible" curve would have resulted. 
Regardless of the length of the interval between 
trappings, approximately half of the rats avoided 
entering traps. This general statement forms the 
major conclusion regarding the recapture response. 
The results indicated no lessening of the avoidance 
behavior toward traps between 18 and 78 days. 
In fact, they indicate a slight enhancement of the 
avoidance behavior. However, little confidence 
may be placed in this difference, for, as may be 
seen in figure 10, rats born during 1947 were pro- 
portionately much higher represented by shorter 
intervals (11 to 40 days) than were the rats born 
during 1948. Thus this difference may, in some 
unrecognized fashion, be related to time of birth. 
Any rat, which avoided capture for 78 days, 
must have lived through a period of trapping 
without entering a trap. After 93 days (i.e. 86 to 
100 days) only 17.1 percent of the rats still avoided 
capture. Such rats which avoided capture for 
86 to 100 days were exposed to at least one period 
of trapping without being captured. Despite the 
crudeness of these figures there can be little doubt 
that the avoidance of traps became markedly 
reduced once a rat went through an entire trapping 
period without entering a trap. As may be seen 
in figure 78, there was a gradual decline in the num- 
ber of rats still avoiding entering traps after in- 
tervals of time longer than 93 days. 
C. Summary of the Alteration of Trap Avoidance 
Through Time. After 1 day following last capture, 
79 percent of the rats avoided reentering traps. 
Days 2 through 6 following last capture had the 
following percentages of rats still avoiding traps: 
69, 64, 61, 60, 59. From 18 to 78 days dollowing 
capture 52 to 66 percent of the rats still avoided 
reentering traps. These two sets of data suggest, 
that, regardless of the time intervening between 
exposure to traps, there is little change in the 
number of rats which will continue to avoid traps. 
However, when a period of nonentering traps 
between two other periods of exposure to traps, 
there is a marked reduction to 17 percent of the 
rats still avoiding traps. This percent gradually 
declines between 100 and 300 days from prior 
capture until practically no rats avoid capture 
longer than this. These trends are summarized 
in figure 79. 
D. Trap Avoidance as Influenced by a Rat's Asso- 
ciates. One female never entered traps over a 
period of 14 months. Several other rats never 
again reentered traps after their first or first few 
exposures as juveniles, even though they lived for 
a year or more. Young rats apparently are in- 
fluenced by the avoidance behavoir (or lack of 
it) exhibited by their older associates. See the 
previous discussion (pp. 85-86) of entering 
the activity recorders. I suspect that this same 
process of mimicking the behavoir of older rats op- 
erated in this trap-avoidance behavoir. If this is a 
correct interpretation of the social influence on de- 
termination or modification of behavior, it is quite 
important in assessing existing or attainable states 
of culture by rats. 
E. Sexual Difference in Frequency of Capture. Four 
hundred and twelve rats inhabiting several Balti- 
more row-house blocks were trapped, marked, and 
released. A number of these reentered traps during 
the initial 5 to 10 day period of trapping (table 1 1). 
Females repeated as frequently as did males. 
The number of males and females available to be 
captured was unknown. Therefore, the only valid 
conclusion is that those females which entered 
traps were as prone as males to reenter. 
The population in the pen exposed to traps was 
known. There were two methods of capture. 
Rats trapped or removed from their places of 
harborage should reflect fairly accurately the sex 
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