that all portions of the home range are not equally 
utilized. There was evidence that from a center 
of orientation there was a regularly decreasing fre- 
quency of visitation to places of greater distance. 
Furthermore, activity was considerably channelized 
by the habit of rats running along trails between 
such centers of orientation as harborage, the food 
supply, or passages through barrier fences. 
Table 38. — The relationship between growth and 
reproduction 
A. 35 adult females examined for placental scars in June 
1949 
Placental 
scars 
Surviving 
progeny 
Mean 
maturity 
index 
Number of 
females 
Yes 
Yes 
1.63 
15 
Yes 
No 
11.21 
16 
No 
No 
11.46 
4 
B. Females born in 1948 who lived to May 1949 
Number of females in each maturity 
Surviving index range 
progeny 
1. 00-1.66 
1. 67-11. 33 
11.34 — III.O 
Yes 
13 
8 
1 
No 
7 
13 
11 
Chi square = 10.043; p less than .01 
In the present section, we shall be particularly 
concerned with the restriction of activities to par- 
ticular sections of the pen by most individual rats. 
In addition, we shall deal with the shifts in place of 
residence exhibited by some rats and not by others. 
Even the 10 introduced rats (table 28 and figs. 
106-108) showed marked evidence of restriction of 
place of activity during the first 7 months of resi- 
dence in the pen. Since there was equal access to 
the Food Pen from all portions of the pen, it might 
be anticipated that each rat would have been 
found as frequently in the southeast and northwest 
halves of the pen, had they formed no attachments 
to a particular portion of the pen. The observed 
distribution for each rat may be tested for its ap- 
proximation to the 50 : 50 ratio by the Chi Square 
(x-yY, 
test, recommended to me by Dr. Ardie Lubin 
*-y, 
for this particular data. The sum of the Chi 
Squares for the 10 animals is 40.86, which with 10 
degrees of freedom is significant at well below the 
0.01 level of confidence. Therefore, it may be 
concluded that the original colonizers did not 
wander about at random, but rather confined their 
activities to particular portions of the pen. 
All animals born in the pen differed from the col- 
onizers in that their places of later residence might 
be influenced by the place of birth. That place of 
birth was an important variable is amply demon- 
strated in table 39A. For rats born in the south 
quarter of the pen, there were 290 captures in the 
south quarter, but only 68 in the opposite north 
quarter. Likewise, for rats born in the north 
quarter of the pen, there were 294 captures in the 
north quarter, but only 44 captures in the south 
quarter. The Chi Square of the difference in these 
two distributions is 295.3, which is significant far 
below the 0.01 level of confidence. It is therefore 
quite clear that place of birth affects the place of 
later residence. 
A more precise appreciation of the degree to 
which rats confine their activities to those portions 
of the pen adiacent to the place of their birth may 
be seen by examining figures 111 to 116. It must 
be recalled that the positions shown in these 
figures denote actual places of harborage or places 
where the rats were trapped. These trapping 
records primarily indicate proximity to place of 
harborage, since rats were regularly observed to 
enter those traps closest to the place where they 
were at that time harboring. Even so, the density 
of records of places of capture depicts quite well the 
actual intensity with which various parts of the 
environment were utilized. A case in point is that 
of the home range of male 22, figure 109. Only 
on one occasion was he observed outside the line 
demarcating his adult home range. This occasion 
was when he was attracted over into Area III by 
the presence of estrous female 43. 
The comparisons between these figures permit 
the formulation of certain conclusions concerning 
home range and the shifts in place of residence: 
1 . There was a marked tendency for the socially 
more dominant rats born in the south quarter 
of the pen to exhibit shifts in place of residence 
such that there was an encroachment upon 
the home range of the socially lower ranking 
rats born in the north quarter of the pen. 
This is particularly well demonstrated by 
figures 114 and 115. 
161 
