6. Closely allied to the situations discussed above 
under 5 is that of extremely low-ranking rats 
in the social organization. They exhibited a 
marked tendency to elicit pursuits by other 
rats. During many periods of observation the 
only chases from the Food Pen were of such 
rats. Several rats of both sexes and represent- 
ing widely separated local colonies would be 
amicably eating or drinking together. Im- 
mediately upon the approach of a low-ranking 
rat one of the members of the feeding or drink- 
ing aggregate would turn and give chase. 
Such chases of markedly low-ranking rats were 
always of much greater length (see fig. 121) 
than between individuals of more nearly equal 
status. The pursuer would then return to the 
Food Pen, and amicably join the group which 
it had just left. If the low-ranking rat soon 
returned, pursuit would again be initiated by 
the same or another rat. It was undoubtedly 
as a result of these chases that such low-ranking 
rats fed during the day when other rats were 
asleep, or fed during those portions of the night 
when other rats were temporarily resting. The 
approach of such a low-ranking rat is charac- 
teristic. It moves forward hesitantly with neck 
and tail outstretched, and presents the ap- 
pearance of crouching with the forelegs. The 
approaches were frequently punctuated with 
slighdy sideways retreats. These behaviors 
announce in no uncertain terms that such an 
individual may be chased with impunity. 
Whereas chases of very low-ranking rats were 
most pronounced from the Food Pen, adult 
females who were lactating or who had estab- 
lished territorial rights in some locality, were 
particularly avid in chasing such individuals 
away from their territory. 
7. See the following section “The relationship of 
estrous females to the frequency of fighting 
and chases.” 
e. The relationship of estrous females to the frequency 
of fighting and chases. When a female is in estrous, 
males are attracted not only to her but to those 
places where she leaves her scent. This attraction 
produced localized increases of contact rate between 
males. However, the increased aggression among 
males is not so much attributable to the increased 
contact rates as such, but rather derives from com- 
petition over priority of engaging in sexual activity. 
Extensive observation made between October 6 
and 8, 1948 (total of 19 hours and 40 minutes of 
observation) amply delimit the phenomena in- 
volved. During this time female 33 who lived at 
the South Alley Burrow was in estrous for at least 
48 hours. The term estrous is here used in the 
sense of heightened attractiveness for males. Dur- 
ing this entire period many males were seen to 
come and engage in sexual rolls at the entrances of 
the South Alley Burrow, at Passage 1, and at the 
passage into the Food Pen, at all of which places 
she had left her scent. Other courting behaviors 
were observed during this period, although sexual 
chases were only seen on the night of October 7 to 
8. No mounts were observed. She apparently had 
just come into estrous on the afternoon of the 6th. 
On this date observations were made only between 
3:20 and 6 p.m. Many rats entered or passed 
through the Food Pen. Most of them drank but 
very few paid any attention to the food. Neverthe- 
less, there was an exceptionally large number of 
fights in or at the entrance to the activity recorders 
attached to the four passages into the Food Pen. 
These were places where females in estrous left 
their scent. When the general observation, that 
few fights occur at the food source, is coupled with 
the specific situation of lack of interest in food on 
this evening, it is probable that the antagonism did 
not arise over food. Although the initiation of 
fights in the activity recorders could only be heard 
and not seen it is presumed that they arose through 
competition over priority of action in engaging in 
sexual rubs against the walls of the recorder. Sev- 
eral fights or chases were observed to arise at the 
South Alley Burrow, when one male approached 
another who was engaged in sexual rolls at burrow 
entrances. 
The males, which engaged in such fighting over 
estrous scent at the South Alley Burrow, were 
either a few of the males born in 1947, or some of 
the larger males born early in the spring of 1948 
at the South Alley Burrow. Fights or chases be- 
tween these same males subsequently occurred in 
the Food Pen. As a result of these interactions the 
aggressiveness of these males became heightened, 
and became directed toward other, and frequently 
much smaller males, who themselves were not 
involved in the sexual activity about the South 
Alley Burrow. These latter males were chased 
about or from the Food Pen, but apparently with 
no reference to direct competition over food. 
That male aggression is heightened by the pres- 
ence of estrous females is particularly well exempli- 
fied by male 22. He was the dominant male of 
183 
