defend territory. However, it is to be noted 
that the two males, Nos. 49 and 690, who 
most markedly defended local regions in 1 949 
were respectively the third and second 
heaviest of all the males. Even so, the 
lighter of these two dominated the other. 
2. Age. If this really is an influencing factor it 
probably operates through the greater weight 
of the older rat and as a result of the older 
rat with its greater experience having an 
advantage over its younger antagonist. Fig- 
ure 123 supports the contention that age is a 
factor. In 1948 it was one of the three oldest 
males who dominated the 10 adult males. In 
1949 the most dominant male was a member 
of the first litter of the season in Area II. 
Three of the other seven dominant males of 
1949 were members of the first litter born in 
1948. 
3. Culture. The characteristics of the mother 
as well as the social condition of the other 
rats inhabiting the vicinity of the place of 
birth appear to provide an important part 
of the determinants which incline a male 
toward becoming a dominant individual. 
Female 15 was the mother of three of the males 
(Nos. 690, 82, and 74) judged to be dominant 
in the spring of 1949. She was the oldest 
female to breed in 1948, and she selected the 
South Alley Burrow as the place for her 
litter (Litter No. 7). It will be noted that 
several lines of evidence showed that the South 
Alley Burrow was the most favorable locality 
in the pen for rats to live. Female 44 was the 
mother of three of the other males (Nos. 49, 
707, and 751), who were judged to be domi- 
nant in the spring of 1949. She was by far 
the largest of the females breeding in 1948. 
This certainly must have contributed to her 
ability to defend her young, for whom she 
was also an excellent provider of stored food. 
Female 44 had moved to Area II shortly 
before she was 4 months of age. This 
move to a locality inhabited by no other 
breeding female in 1948 enabled her to rear 
her young without the added competition of 
social pressure from other juveniles or from 
lactating females. Whereas, such rather in- 
definite cultural attributes as discussed above 
may at first appear to form a rather frail basis 
for judging their importance in contributing 
to the eventual dominant status of a male, it 
is noteworthy that for practically all other 
litters bom in 1948, and which did not pro- 
duce dominant males, there were one or more 
unfavorable conditions surrounding the early 
life such as excessive competition with other 
juveniles or lactating females, low weight of 
the mother, or past history of social sub- 
ordinancy of the mother. 
If the pattern of male dominancy revealed in 
this study is also true of rats living under other 
wild states, it has particularly relevance to gene 
flow through the population. Wheras, females, 
particularly those that are successful in rearing 
young remain at the place of their birth, males 
tend to become dominant in some other area than 
their birth. Furthermore, since those males which 
are quite dominant do exclude other males, includ- 
ing the sibs of the females in question, the degree 
of inbreeding (see pp. 142 to 143) will be lessened. 
I. Development of Local Colonies. During the 
breeding season of 1948 and continuing through 
the nonbreeding winter season of 1948 to 1949 
shifts in place of residence occurred (table 30). 
These were primarily from the southeast half of 
the pen toward the northwest half. This shift 
was from the area of higher social status, with its 
higher rate of production of young, to the region 
of lower social status, with its lower rate of produc- 
tion of young. Gradually through the winter the 
shifting about lessened, and local aggregates or 
colonies developed more constancy of membership. 
In fact, by the beginning of the breeding season in 
early March, the membership of local colonies 
(fig. 128) became so rigidly fixed that there were 
few further changes through the remaining history 
of the pen to late May 1949, at which time all rats 
were captured and killed. 
The composition and history of these local colo- 
nies throws considerable light upon the nature and 
implication of social organization in the Norway 
rat. A local colony is considered as any group 
inhabiting a single burrow system, or as any group 
in which, for whatever reasons, the members had 
much more frequent associations with each other 
than with other rats. 
Six criteria were used for judging the relative 
social rank of a colony. They were: 
1. Proportion of the group which remained near 
the place of birth. The greater the proportion 
remaining near the place of birth, the higher 
the social rank. 
203 
