Figure 38. — The female is pushing balls of mud into place with her nose so that they block the entry. 
farther down within the burrow. Photograph by U.S. Army Signal Corps. 
These balls are formed 
had poorly developed temperature regulatory 
mechanisms should be of survival value. The 
type of sealing characteristic of lactating females 
is the pile of vegetation over the burrow entry. 
This behavior is very similar to another one fre- 
quently exhibited by mothers of new born young, 
which is to cover the young with a layer of vege- 
tation such as forms the nest. 
Low social rank tends to increase the frequency 
of this sealing behavior. A specific series of ob- 
servations relates to the three females (17, 20, 
and 25) of litter 3, who were frequently found in 
association with each other. See pages 186 to 196 
for further documentation of conditions indicating 
the low rank of these females. On eight occasions 
between November 1947 and September 1948 these 
three rats were involved in the sealing of the drain 
tiles going down into harborage boxes. Only one of 
these was associated with a parturition, and this 
litter was not raised. In fact only one of the 12 
litters conceived by these females was believed to be 
raised to weaning. All the others must have died 
within a day or two after birth. Of course the 
state of potential lactation may have influenced 
the occurrence of observed tile plugging with 
vegetation by these females. 
The distribution of the location of burrow sealings 
also gives some support to the belief that this 
behavior has a higher incidence among socially 
low ranking individuals (see table 2). 
As will be documented later in this paper, there 
were two regions in the pen whose members were 
differentiated both on the basis of genetic lineage 
and social history. These two regions were (A) 
the South Alley and Area I and (B) the North 
Alley and Area III. Between these two regions 
38 
