pened that rats encountered initially in one area 
were found in another area by the time these later 
boxes were opened. Often the place of the second 
observation was outside the rat’s normal range, 
and was with another rat with whom it infrequently 
associated. 
4 . The Responses of Rats to Traps 
Traps, used to capture the rats alive, also elicited 
an avoidance reaction. So much data was ac- 
cumulated with reference to the avoidance response 
of the rats toward the traps that various aspects of 
this phenomena are treated separately in this and 
the following sections. 
Although wooden traps were normally used with 
fair success, a commercial Havahart trap was also 
tried out. These consisted of wire mesh walls and 
solid metal treadles and doors. Doors occurred at 
either end so that when the doors were propped 
open it was possible for a rat to travel through the 
trap. Two of these traps were received in Decem- 
ber 1947. These were initially placed with doors 
propped open along well used trails. After 2 days 
the treadles were still shiny; that is there were no 
muddy foot prints on them as would have been the 
case had the rats passed through. A similar test 
was made on a later date. On this date the rats 
were intensively using a trail worn through the 
snow from the North Alley Burrow to the Food Pen. 
During the night that the trap was placed along 
this trail, with both doors propped open, the rats 
diverged around the trap and never disturbed the 
snow in the bottom of the trap (see fig. 76). These 
two traps were also set during the December 1947 
trapping period. Yet the only rat caught was the 
socially very low-ranking female No. 25, and she 
entered one of these traps twice. During the next 
year and a half the few rats caught in this type of 
trap were invariably juvenile or socially low- 
ranking adults. 
This tendency of socially low-ranking rats to 
exhibit a reduced avoidance of traps is so character- 
istic that it forms a portion of the syndrome of 
abnormal behavior discussed with respect to the 
extremely socially low-ranking rats in a later 
section (p. 195). 
At irregular intervals (46.4 days, ±2cr of 14.5 
days) wooden box traps (9) were set. Traps were 
left set for 3 to 8 days during each of these periods 
of trapping (fig. 10). Groups of traps were con- 
centrated about all the places of harborage, at the 
passages through the barrier fences, and along the 
most frequently used trails. Thus all rats must 
have had several opportunities for entering traps 
on each night they were set. Furthermore, traps 
were in an adequate excess to insure the presence 
of many unset traps throughout the night. There- 
fore, any lack of capture indicates a failure of the 
rat to complete his response to the bait in the trap. 
Bait placed in the traps included such items as 
sunflower seed, horse feed, sweet potato, bread, and 
oranges which were known to be highly attractive 
to the rats. When such food was made available 
in the Food Pen, but not in traps, the rats would 
ignore the Purina pellets at the hooper until this 
temporary type of food was all eaten or stored. 
This preferred food represented a reward or posi- 
tive reinforcement of the response of entering the 
trap. Once trapped the rat was exposed to a series 
of events which served as a punishment or negative 
reinforcement of the response of entering traps. 
The following conditions contributed to the un- 
pleasant aspects of the experience: 
1. The door falls with a bang. 
2. The door may fall on the rat’s tail. 
3. The rat is confined to a small space, usually 
for 10 or more hours, from which there is 
usually no escape. During this time the rat 
is prevented from engaging in the many 
activities in which it otherwise would have 
been participating. 
4. The rat is exposed to the weather during the 
period of confinement. 
5. The food supply is inadequate and no water 
is available. 
6. When two rats are simultaneously trapped, 
intense fighting frequently occurs. This is 
even true of juvenile rats, who very infre- 
quently engage in such fighting outside of 
traps. 
Despite these unpleasant aspects of the experience 
rats do reenter traps. When this happens it 
must be concluded that the positive attraction 
of the trap exerts a greater influence than do the 
negative repelling aspects. The data on retrapped 
rats provides some insight into this balance. 
Many observations of rats from the tower sub- 
stantiated the inference from trapping data that 
rats do develop a marked avoidance behavior 
toward traps. The pattern of behavior was one 
of repeatedly approaching a set trap whose door 
was held open by the trigger stick. These ap- 
proaches were followed by backing or turning 
88 
