Table 27. — Accumulated total of food beliefs eaten 
Location 
Mean dis- 
tance (feet) 
from prior 
food source 1 
Mar. 9 
Date 
Mar. 11 
Mar. 14 
Area IV 
38 
47 
174 
240 
Area III 
108 
0 
35 
152 
Area II 
178 
0 
25 
56 
Area I 
43 
80 
146 
1 Between Passage 1 and outside fence and calculated in 
a clockwise direction through the areas. 
From these observations it must be concluded 
that exploration by rats in a new environment 
away from a discovered source of food is only 
sufficient to satisfy their current needs. However, 
as each new source is depleted, further peripheral 
exploration ensues. 
B. Regional Differentiation of Major Social Groups. 
On March 15, 1947, the permanent food hopper 
was placed in the central Food Pen. During the 
next few days rats utilized all harborage boxes, 
passages through the barrier fences, areas, and 
alleys. In fact, once the 30-day period of “teaching 
and indoctrination,” by the experimenter, had been 
completed, the rats exhibited a marked increase in 
ranging. Within the space of a few minutes a rat 
might cover fully half of the entire pen and from 
day to day it might shift its place of residence from 
one area to another. 
By March 22, 4 of the 14 rats had died. One 
female was found in a state of poor motor coordina- 
tion which lasted for several hours until she died. 
One rat was accidentally caught in a steel trap. 
Two others were accidentally sealed and suffocated 
in their burrow. The 10 surviving rats at the time 
of completion of the adjustment to the pen were 
designated as the original colonizers. 
A summary of the history of these colonizers is 
given in table 28. They were arbitrarily divided 
into two groups, Southeast and Northwest rats, in 
accordance with which side of the pen the rat 
inhabited more frequently. This was done because 
the later history of the colony indicated a sharp 
division of the colony. Rats living on the South- 
east side, Areas I and II and the South Alley 
Burrow, exhibited much more favorable character- 
istics of social status, growth rate, reproductive rate 
and survival. It was desired to determine if the 
initial history represented by the colonizers gave 
any indication that this partition began immedi- 
ately. 
With regard to weight, the two heaviest males 
and the two heaviest females were members of the 
Southeast group. With regard to survival, four 
members of the Northwest group died before any 
of the Southeast group did, and four of the South- 
east group lived 2 or more months after all of the 
Northeast group had died. With regard to 
pregnancies, each of the three Southeast females 
conceived three times; whereas only one of the 
Northwest females became pregnant, and it only 
twice. Both groups had poor survival of litters. 
Only 3 of the 11 litters survived. This is probably 
an indication of the marked tension and lack of a 
stabilized social structure characteristic to the 
colonizers. 
With regard to social status, the most dominant 
female was southeast female No. 10, and the most 
dominant male was southeast male No. 6 (see pp. 
179-203 for criteria utilized in judging domi- 
nance). Furthermore, following the death of this 
male (p. 198 and two of the other males, southeast 
male No. 12 was dominant to the surviving north- 
west male No. 8 The later history of male No. 12 
exhibits his cognizance of this geographic relation- 
ship to social status. As may be seen in figure 107 
there was a shift in place of residence corresponding 
to his reduction in social rank in 1948. The young 
born to the colonizing females also reflect this social 
stratification with reference to place of residence. 
Females 17, 20, and 25, the only surviving members 
of the litter (L-3) born on the northwest side of the 
pen showed a reduced growth rate (fig. 141, graph 
31) and extremely low social status in relation to 
the 1 3 surviving members of the two litters born on 
the southeast side of the pen. Figure 141, graph 33 
shows the more rapid growth exhibited by the 
females born on the southeast side. 
Considering the marked fighting that did occur 
among the colonizers it is probable that the differ- 
ence in distribution that developed was not a chance 
one, but rather resulted from social action. Al- 
though the number of individuals was small, the 
consistent trends favoring the Southeast rats with 
regard to size, survival, reproduction, and social 
status support the reality of this initial division. 
Once the rats had become adjusted to their new 
environment there was a marked difference in the 
tendency to aggregate from that occurring when the 
rats were confined in the Food Pen between Feb- 
ruary 4 and 12. On 11 surveys of the harborage 
138 
