These give a distribution as follows: 
Number of rats in a harborage box or 
burrow 
Times 
observed 
0 
7 
1 
4 
2 
2 
3 
0 
4 
4 
5 
1 
6 
4 
7 
0 
8 
1 
9 
o 
10 
0 
11 
1 
During this period considerable food was trans- 
ported from the central food box to the four harbor- 
age boxes. Thus three behaviors; climbing fences, 
transporting food, and digging burrows, which in- 
volved manual ability, were known to be charac- 
teristics of the introduced rats. Furthermore, the 
tendency of the rats to occur in groups indicated 
social attraction. 
Stage 2: February 13 to 17. Passages 5 to 8 into 
the Food Pen were opened. Other than for an 
occasional wandering out into the surrounding 
“Alley” the rats confined their activities entirely to 
the Food Pen. There was no evidence that the 
rats ever went into the “Areas”. This indicated a 
strong tendency of rats introduced into a strange 
environment not to wander far from a known source 
of food and harborage. 
Stage 3: February 18 to March 6. The food box 
was shifted to a position just below the observation 
tower between Passage 1 and the outside fence. 
This was done in an attempt to initiate explora- 
tions farther away from the centrally located Food 
Pen. On February 18 a trail of food was placed 
from the Food Pen to the new food source. During 
the next 2 nights the rats made the adjustment of 
going to the new location of food. Other wander- 
ings, than that between the Food Pen, where the 
four harborage boxes were located, and the new 
source of food, were primarily confined to running 
back and forth along the southwest outside fence. 
On February 20 a burrow was dug in the loose 
soil by the fence opposite Box 36. This was in 
addition to three burrows then in the Food Pen. 
A blanket of snow covering the ground between 
February 23 and March 6 permitted an accurate 
determination of the rats’ wanderings. Wander- 
ings were primarily confined to those within the 
Food Pen, between the Food Pen and the food 
source opposite Passage 1 and between the food 
source and the burrow opposite Box 36. Rare 
wanderings occurred about the alley and through 
Area IV. There were rare wanderings into Areas 
I and II. No rats entered Area III. Along the 
heavily traveled routes the rats would make 
occasional short journeys of a few feet to one side 
before returning to the main route. The observa- 
tions provide further support to the thesis that rats 
in a strange environment confine their activities 
to nearly the minimum imposed by the necessity 
of going back and forth between the sources of 
food and harborage. No rats entered any of the 36 
sunken harborage boxes. 
Marked competition, particularly in the form of 
fights and chases about the food source, occurred. 
In fact, the amount of fighting between the intro- 
duced members from this time through the summer 
of 1947 was greater than that among any com- 
parable number of rats during the remaining his- 
tory of the colony. Although this is a qualitative 
impression, I am convinced of its validity. It was 
this inability of rats which lacked a common prior 
history to develop a stable social structure with a 
minimum of fighting that probably accounts for 
the initial difficulty of this group of rats in repro- 
ducing and establishing itself. 
Stage 4: March 7 to 14. The final stage in the 
adjustment of the rats to the pen was to induce 
them to go into the sunken harborage boxes and 
to utilize more equally the various parts of the 
pen. In order to accomplish this objective (a) 
the temporary harborage boxes were removed 
from the Food Pen, (b) garbage was placed in one 
box in each area (Boxes 3, 12, 21, and 30), (c) 30 
Purina food pellets were placed in each of the other 
boxes. 
Food was first removed from the boxes in Area 
IV near the burrow opposite Box 36. From here 
the removal of food on succeeding days indicated 
that the rats were gradually moving around the 
areas in a clockwise direction (table 27). The rats 
immediately began eating pellets in the boxes of 
Area I nearest Passage 1. However by March 14 
only 22 of the 90 pellets in Boxes 4, 5, and 8 in 
Area I and only 4 of the 90 pellets in Boxes 10, 
11, and 15 in Area II had been eaten. This 
indicated that the rats did not move in a counter- 
clockwise direction from Area I to II during this 
period. 
676-768 O — 63 10 
137 
