Area I during 1948, and there exhibited territorial 
defense. Although he was observed many hundreds 
of times in the Food Pen eating with other rats he 
was only noted to engage in fights or chases in the 
Food Pen on two dates, July 7 and October 7, 
1948. On both of these dates female 33 was in 
estrous at the South Alley Burrow. This burrow 
lay along his most frequendy traveled route be- 
tween Area I and the Food Pen. He definitely 
dominated the South Alley Burrow at these times 
with reference to priority of action in engaging in 
courtship behavior. For this reason his territory 
of Area I might be considered as also extending 
over the South Alley Burrow. At least this domi- 
nance on his part may account for the fact that no 
other male developed a territory encompassing the 
South Alley Burrow during 1948. The range (fig. 
109) of male 22 was normally restricted to Area 
I and the routes directly connecting it with the 
Food Pen. The only times he was observed roam- 
ing out of it as an adult was when he was attracted 
into Area III and IV by the presence of estrous 
females. On each of these three occasions he was 
noted to engage and win combats arising at scent 
“posts” left by the estrous females. 
By the night of October 7 to 8, 1948, a general 
change in behavior of the rats had occurred. Even 
during the same hours on which observations were 
made on the previous day there was now a marked 
attraction of the rats toward the food and a nearly 
complete cessation of fighting in the activity re- 
corders. The lack of fighting at these points is most 
probably attributable to the decline in attraction 
of estrous scent left at the passages into the Food 
Pen. By the second day of estrous the expanded 
range characteristic of females on the first day of 
estrous has not only been reduced; it is actively 
restricted to less than normal. This arises from the 
fact that she is essentially restricted to the vicinity 
of her home burrow by the persistent approaches 
of males who give her little opportunity to go to 
the Food Pen. On this night fighting again oc- 
curred among males about the South Alley Burrow. 
The males exhibiting this heightened aggression 
again transferred this aggression toward other males 
whom they chased from the Food Pen. However, 
the evidence again was that this aggression had 
only indirect relation to the procurement of food. 
It might be added that aggression by females 
also appears to be increased at the time other 
females come into estrous. Females not in estrous 
are attracted to the places where estrous females 
184 
leave their scent. There they exhibit sexual rubs 
or rolls and give chase to males which encroach 
upon these activities. During such times the level 
of aggression of those females, who have had the 
opportunity to be stimulated by the estrous scent, 
becomes heightened to the point that aggressive 
actions, particularly against other females, occur 
in other places, such as in the vicinity of the Food 
Pen, where normally little interfemale aggression is 
expressed. The female who is in estrous exhibits 
heightened aggression at the terminal portion of the 
period when she is sexually attractive to males. At 
this time her receptivity toward males is extremely 
slight. She then actively repels their advances. 
She also may exhibit increased aggression toward 
other females at this time. 
f. Territoriality — expulsion of strangers from burrows 
or harborage boxes. Occasionally rats, which were 
completely undisturbed by the observer, were noted 
to visit areas outside of their normal ranges and 
there enter places of harborage. The normal 
course of events was that the stranger would 
abruptly emerge squealing as if bitten by the resi- 
dent rat, which normally emerged no farther than 
to protrude its head from the entrance. Occa- 
sionally such an invading rat would also be chased 
from the vicinity. A case in point is the following: 
1. On April 29, 1949, at 4 p.m. male 669 was 
seen to enter Area I and enter Box 7. A fight 
could be heard inside (the observer had been 
standing quietly nearby). Male 669 emerged, 
followed by male 690, the dominant male of 
Area I, who chased him to Area IV. Male 
669 was a member of the socially low-ranking 
aggregate (colony h, p. 212) inhabiting the 
central portion of Area IV during the spring 
of 1949. 
2. Female 28, who was the dominant female of 
Area I; occasionally stopped in the South 
Alley Burrow on her way to and from the 
Food Pen. On May 18, 1948, she was seen 
to squeal and jump out of the SAB hole 8 as 
if she had been bitten on the rear. Pre- 
sumably her ejection was by the lactating 
female 37 whose litter was located in this 
portion of the burrow. 
These two records are typical of this expulsion. 
Although socially low-ranking rats were more fre- 
quently noted in such expulsions, it was quite 
apparent that regardless of the social rank of a rat 
about its own home, any invasion by it into the 
homes of rats in other localities was likely to result 
