On several occasions a raw unbroken hen’s egg 
was placed in the Food Pen. Although the rats 
rolled it about on the ground they were never 
able to break the shell. There are many popular 
reports relating to the ability of rats to break or 
transport hen’s eggs. If there is any validity to 
these reports it is likely that the behavior is a 
culturally developed behavior which has a low 
probability of spontaneous origin. 
Natural food stuffs occurring within the pen 
played an insignificant role in the nutrition of 
the rats. On a few rare occasions rats were ob- 
served to eat blades of grass. Bark from the 
trees also served as an occasional source of food. 
Dogwood, Virginia pine and black locust were 
the only trees of any abundance in the pen. Of 
these the locust was the only one which seemed 
to be eaten to any extent. Many of the locust 
trees were severely damaged, even far up in the 
branches, although few trees were killed. Even 
so this bark supplied only a minute portion of 
the diet of the rat. Otherwise, when the population 
was high, these trees would all have soon been 
killed. On two occasions the groups of fasicles 
forming the tips of pine boughs were mixed through 
caches of Purina checkers in such a manner as 
to indicate that their transportation was a food 
storage behavior, even though no evidence was 
ever obtained that the rats ate pine needles or 
stems. On one of these occasions several hundred 
such tips of branches were mixed through a huge 
cache of 2200 Purina checkers, the composite 
mass of which completely filled a harborage box. 
This depositing of pine fasicles among actual 
particles of food is interpreted as a disruption of 
discrimination by chronically disturbed rats. The 
rats involved in this aberrant behavior were 
female 43 and members of her three litters de- 
scribed on pages 147 to 148 These same rats 
were those excluded from Area III by more 
dominant rats in the formation of Colony e during 
the early spring of 1949 (see pp. 207 to 209). 
Also see pages 195 to 196 for details of this and 
related behaviors of the rats involved. 
During the spring of 1947 when there were 10 or 
less adult rats, small piles composed of 1 to 8 earth- 
worms were found in the harborage boxes. In 
most cases only parts of each earthworm were 
present. 
Other than these few instances, the rats were 
forced to depend entirely upon the supply of Purina 
laboratory checkers provided for them directly in 
the center of the Food Pen. 
B. Behaviors about the Source of Food. The dimen- 
sions of the Purina checkers were approximately 
10 by 18 by 20 mm. These were removed one at 
a time at the time of eating or transporting. 
Occasionally the rats would rake out small piles 
with their forefeet much in the manner of excavat- 
ing dirt from burrows. This behavior became 
highly exaggerated on one occuasion when a 
smaller sized food particle was provided. This 
commercial food was in the shape of small cylinders 
approximately 5 mm. in diameter and 15 mm. long. 
The use of this food had to be discontinued since 
the rats excavated the entire 100 pounds the first 
night so that it formed a concave mound about the 
hopper. Under these conditions the rats responded 
more to the food as materials for excavation than 
as items of nutrition. 
Invariably any object of food picked up was 
initially grasped with the teeth. Occasionally an 
upward raking motion with one forepaw might be 
used to facilitate the grasping of larger objects by 
the teeth. However, this use of the forepaws never 
appeared to be very effective. With smaller 
objects, such as the Purina checkers, there would 
be a transfer to the forefeet, as the rat sat on its 
haunches. The rats rotated such objects profi- 
ciently while eating. Regardless of the size of the 
food object, rats frequently just nibbled on it in 
the position which the food happened to be lying. 
Rats were never observed to transport more than 
one Purina checker at a time. On only one occa- 
sion was a rat seen to attempt to transport two 
pieces of food as large as a Purina checker. This 
rat grasped a piece of meat, shook it back in its 
mouth and picked up a roll. Halfway to its bur- 
row it dropped the roll and had to return. With 
small objects such as dry corn meal the rats will 
transport them by the mouthfull. Objects the size 
of a slice of bread or a carrot are picked up with the 
teeth, and with the head slightly tipped back on 
the shoulders the rat runs forward. When the rat 
reaches a passage through a fence or an entrance 
to a burrow with such a piece of food it drops it, 
goes through, turns around, comes back, and then 
pulls the food through. Objects too heavy to carry, 
and these may weigh as much as the rat, are 
dragged along as the rat grasps them with its teeth 
and backs along. 
As soon as the population had increased to 30 
individuals it was not uncommon to see 10 to 15 
100 
