April and May 1949, he lived under the 
exposed ladder in the East Alley with several 
other outcasts (colony k, p. 213). 
These records help to emphasize an important 
point. This is that, although rats may be expelled 
from harborages which they do not customarily 
enter despite their social rank, the frequency of 
expulsion is greater for socially low-ranking rats. 
In fact, I have been lead to the hypothesis that 
the number of places of residence is inversely 
related to social rank of the individual (see dis- 
cussion of the homogeneity index on p. 214). 
Certainly, much evidence of this relationship 
could be cited. Only the opposite extremes will 
be mentioned. On the one hand there were 
several females born at the South Alley Burrow 
which were practically never caught anywhere 
else but at the place of their birth, and for whom 
all lines of evidence point to their high social 
status. On the other hand, there were such 
individuals as the female sibs, 17, 20, and 25, 
who were practically never caught at the same 
place on two successive captures, and for whom 
all lines of evidence pointed to their extremely 
low-social status. 
A striking example of the exclusion of other rats 
by the residents of a place of harborage is the fol- 
lowing. On the night of January 6-7 a large nest 
of pine boughs was constructed in the activity 
recorder at Passage 6. This nest was utilized on 
that night and the following one by females 44 and 
48, and males 29 and 670. Forty-four and 
twenty-nine were sibs, while 48 and 670 were not 
only sibs but young of 44 with whom they were 
remaining although 298 days of age. On January 
8 this nest was examined in detail. It was both 
clean and well formed, thus indicating that the 
many rats which normally passed through this 
activity recorder had not done so during these two 
nights. This was the only record of rats building 
a nest in an activity recorder. Furthermore, these 
four individuals were among the eight taken out 
of Box 12 on January 6. Their movement as a 
group is one line of evidence which shows that rats 
do organize into groups which may maintain their 
integrity in moving through space. 
g. Defensive territoriality — hole-plugging. From time 
to time rats plugged the entrances to harborage 
boxes or burrows with vegetation, soil or rocks. 
Such plugging inhibited the entrance by other 
rats. In this sense the rat exhibiting hole-plugging 
behavior is possibly defending the limited space 
it is inhabiting. This sealing of entries into 
harborages was previously discussed in detail 
in the section titled “Alteration of Burrows” 
(pp. 30 to 42). The one point which may be 
reemphasized here is that hole-plugging occurred 
three times as frequently in the north quadrant of 
the pen, which was inhabited by rats of relatively 
low status and who weaned only half as many 
young as the rats of higher status inhabiting the 
south quadrant. 
This passive territorial defense was frequently 
associated with a lactating female, although even 
here it was affected by social status. Among the 
South Alley Burrow mothers, with their higher 
social status, there were only eight observed 
instances during 1948 of hole-plugging. These 
involved litters 10, 15, and 25b of females 33, 37, 
and 17. No pluggings were associated with litters 
7, 17, 19, and 32-37. In contrast to this there were 
13 records of hole-plugging by the socially lower 
ranking female 42 at the North Alley Burrow. 
Covering of holes by her was more marked right 
after the birth of the young. Yet she persisted in 
this activity during the entire period of lactation. 
It is also of note that the two females, 37 and 75, 
who were excluded from the South Alley Burrow 
during the summer of 1948, did cover entrances to 
their burrows in Area IV when they had litters. 
There was also a qualitative difference in the 
coverings between the North and South Alley 
Burrows. Those at the North Alley Burrow were 
much larger and functionally more effective. 
h. Offensive territoriality. Included under this 
topic are all those instances where an individual 
repeatedly and aggressively drove off other rats 
which invaded the general locality about a single 
burrow or a group of neighboring harborages. 
Unless occupancy of a particular space may be 
considered a goal in itself, territorial behavior of 
this type is in quite a different category from the 
more frequent combats associated with priority of 
action such as involved in the competition of males 
over a female in estrous. Territorial defense was 
exhibited by most lactating females, and by those 
few males who were able to dominate a harem of 
females to the nearly complete exclusion of all other 
adult males. The most characteristic aspect of this 
territorial behavior was that the rat exhibiting 
territorial defense rarely showed any antagonism 
to rats it encountered while outside the territory, 
not even toward individuals whom it may have 
186 
