The females of colony g were probably a discrete 
subgroup from the males assigned to this colony. 
The sections of the burrow system which they in- 
habited had become isolated as a result of the 
collapse of a nest cavity. See the arrow separating 
these two sections in figure 22. The collapse of 
nest cavities is an indication of overcrowding which 
is more characteristic of socially disorganized 
groups. When there are too many rats in a nest 
cavity, they more rapidly scratch off the roof to 
the point of its collapse. The three males were 
the slowest growing of any aggregate. Living di- 
rectly in front of Passage 4 exposed them to con- 
tinual disturbance by the many rats from Areas 
III and IV which passed through Passage 4. This 
coupled with their small size, and the known 
indications of disturbance of male 59 strongly sug- 
gests that they were accessory males who did not 
participate in reproductive activities. 
The most striking fact about the females of colony 
g was that seven of them along with their mother 
were born at approximately the position where they 
were found in May 1949, and yet none of them had 
surviving young. In fact, only two other of female 
42’s daughters lived elsewhere and they were non- 
reproducing members of the neighboring colony 
f in Area IV opposite Box 28. Whenever one of 
them came into estrous it was pursued all night by 
a pack of males from colonies f and j. Of the 
several females so noted, 674, happened to be 
marked at the time. On the basis of her frequently 
exhibiting lordosis during copulation, intromission 
probably occurred. Yet when she was killed 6 
weeks later she had only six placental scars and 
there were no surviving young from the 3 months 
of the spring breeding period. All other females 
here had similar histories (see p. 155). 
These 13 females lived in 4 nest cavities. This 
crowding alone may well have led to the death of 
any litters born. In contrast to this, the 1 3 females 
of colony a, South Alley Burrow, had 10 nest 
cavities in which there were nests as well as 1 1 other 
cavities in which nests could readily be constructed. 
Thus, in colony a there was a cavity containing a 
nest for each female with a litter. Where there is 
not ample space in the burrow for a female to live 
in isolation at the time of parturition and following 
it, the normal response is to construct a new burrow 
during the day or two prior to parturition and to 
construct a nest in it. 'The failure of these responses 
to be exhibited in sufficient degree to isolate the 
parturient females of colony g suggests that these 
responses are inhibited in females under stress. 
Colony h: Central Area IV ( table 53). 
The rats of this colony most frequently utilized 
Passage 1 enroute to and from the Food Pen. This 
exposed them to the antagonistic actions of male 
49, the dominant male of the South Alley Burrow, 
colony a, as well as to that of the lactating females 
residing there. Colony h rats were most closely 
associated with the all-male colony k. Many of 
these colony k rats exhibited two loci to their home 
ranges. They spent the majority of their time in 
the area of the East Alley between the burrow by 
Passage 3 and Passage 6 into the Food Pen. Yet 
rather frequently some of these rats would leave 
the Food Pen in just the opposite direction and go 
over into Area IV by way of Passage 1. Despite 
separation in space colonies h and k might well be 
considered as a single unit. The intermingling of 
these two colonies is another line of evidence which 
leads me to believe that rats which have arrived at 
relatively the same social status are actually at- 
tracted to each other. There is nothing particu- 
larly noteworthy about the males of colony h, 
but the females require comment. Of the 35 
females in colonies a to h which were examined for 
placental scars only four failed to have any. This 
suggests that these four never conceived. Three of 
these nonconceiving females were members of 
colony h. Furthermore, they were physically all 
very slow maturing. Of the 59 females in colonies 
a to h, which were born in 1948, there were only 
10 whose Maturity Index was over 1 1. 5, yet 4 of 
these were at colony h. The comparison of the 
number of females with Maturity Indices over and 
under 1 1.5 in colony h and elsewhere has a Chi 
Square of 15.081, with a probability by chance far 
less than 0.01 . These females were exposed to more 
males than were any other group of females. They 
may be considered as having rather close associa- 
tions with the 30 males of colonies h, i, and k. 
Colony i: Areas I to IV Marginal Colony ( table 54). 
These 13 males were primarily (12 out of 13) 
those which maintained the closest association 
with their places of birth in so far as geographic 
position was concerned. 1’hey inhabited a bur- 
row against the outer fence opposite Passage 1 
as well as the three nearest harborage boxes in 
Area IV. However, they were very effectively 
excluded from the vicinity of the South Alley 
212 
