area, particularly with reference to Area IV and 
and the North Alley. Male 786 must have dis- 
persed this aggregation of large males at the be- 
ginning of the breeding season. Males 82, 74, and 
89 went to the adjoining .Area IV and the North 
.Alley where 82 and 74 were presumably dominant 
males (see colonies f and j, pp. 209 to 212). 
Male 909 moved back and joined the marginal all- 
male group opposite Passage 1 (colony i, p. 212). 
Male 657 became one of the outcast members of 
the East Alley Group. Thus large size did not 
insure a dominant place for these males (colony 
k, p. 213). 
Since males who were dominant in different lo- 
calities were rarely observed together it is difficult 
to assign an exact rank order to them. However, 
I am inclined to believe that male 82 was the next 
highest ranking male after 49, 690, and 786. These 
were the only males exceeding 82 in weight and 
82 had apparently been excluded from Area III 
by 786. The basis for designating him as the 
dominant male over the area shown in figure 127 
was that he w r as observed to repeal other males 
engaged in chases of estrous females, although he 
apparently rarely mounted the estrous females. 
However, his dominancy was not one of territorial 
defense as was that of males 49 and 690. He 
tolerated the presence of several other males in this 
central portion of his home-range, nor could he 
prevent the passage through it of males from all 
immediately surrounding regions. Two factors 
contributed to this apparent quasi-dominant status. 
He was the oldest and largest male born in 1948, 
who later most frequently inhabited Area IV. He 
was bom in the socially most favorable colony of 
the pen at the South Alley Burrow. 
Regardless of his actual rank among the domi- 
nant males, No. 707 exhibited an interesting rela- 
tionship in his dominancy over the burrow in the 
South Alley by Passage 2. He was a younger 
brother of male 49 w'ho dominated the neighboring 
South Alley Burrow and with whom he must have 
had considerable interaction during his early life 
(see p. 200). By February 1949 he and three of 
his sisters as well as his mother had moved to this 
location from Area II. All during the breeding 
season he persisted in invading the surface area of 
the South Alley Burrow, when females residing 
there were in estrous, and when male 49 was 
absent. However, he exhibited marked avoidance 
behavior whenever male 49 approached, or when 
they encountered each other in the Food Pen. 
Although none of the 10 females of the South Alley 
Burrow, who conceived one or more times during 
the 1949 spring breeding season were ever seen in 
the act of copulation, and although male 707 was 
only slightly greater than average size (mean life 
span Maturity Index of 1.86) it is highly probable 
that if any male other than 49 contributed to these 
conceptions it was male 707. 
At the North Alley Burrow there was no clear cut 
dominance. As has already been mentioned, male 
82 from Area IV partially shared control of this 
burrow. Of the 12 males (tables 52 and 53) resid- 
ing in this general locality male 74 probably held 
the most dominant status. Although 4 of the other 
11 males were of approximately the same weight 
as male 74, he was repeatedly observed to whip in 
combat other males who participated in the sexual 
chases of estrous females about the North Alley 
Burrow. 
The designation of the dominance of the final two 
males was based upon more circumstantial evi- 
dence. Male 97 was assigned as the dominant male 
of the all male aggregate inhabiting the alley region 
about Passage 3 solely on the basis that he was the 
heaviest of the 13 males (table 55) and was the only 
one that had not lost considerable weight. Of the 
two males inhabiting Area II (table 47), male 751 
was assumed to be dominant over male 95. Three 
lines of evidence lead to this conclusion. First, 
male 751 continued to grow during the 1949 spring 
breeding season until he surpassed male 95 who 
had declined in weight. Second, male 751 had 
continued to reside near the place of his birth while 
male 95 was known to have been driven from his 
place of birth, Area I, by male 690. Third, two 
of male 751’s sibs, males 49 and 707 were definitely 
known to have dominated local areas. This points 
to the favorable condition of his early life. 
a. Summary of Male Dominance and Its Implications. 
It was impossible to determine all the conditions 
which influenced the acquisition of dominance or 
the selection of an area to be defended. However, 
the histories of the males discussed above strongly 
suggest certain conditions. 
1. Weight. During the 1947 season weight 
alone seemed to determine dominance. It 
is to be noted that because these rats were 
colonizers there was little likelihood of culture 
influencing the outcome. Later other factors 
than weight certainly operated. Male 22 
defended Area I in 1948 despite the survival 
of two of his larger brothers who did not 
202 
