Presumably this was the cause of the invasion of 
this burrow by six 63- to 105-day-old subadults. 
Upon excavation of this burrow on June 21 the 
hooded nest was found collapsed upon the young 
by the six rats then occupying the burrow. The 
mother was not in the burrow. Presumably she 
was away from the burrow being sexually pursued 
by a pack of males while this happened. Although 
the young were not quite dead they were not 
accepted later by their mother. Under more nor- 
mal conditions this mother exhibited good maternal 
care as evinced by her successful rearing of several 
litters. 
The stage of maturation of the mother, including 
prior experience in handling and caring for young, 
appears to be an important factor in the success of 
the mother in rearing her young. A case in point 
is that of 187-day-old primiparous female 48. She 
was found on September 18, 1948, with several 
newborn young on a simple pallet nest in Box 14. 
Her litter disappeared so soon after birth that 
little or no nursing had occurred, since 3 days 
later her teats were in the one-plus nonuse state. 
It will be noted that both the behaviors of nest 
building and maternal care were poorly expressed. 
During the spring of 1949 she successfully reared a 
litter. Upon autopsy in June 1949 she had only 
16 placental scars. This indicates she had only 
these two litters. A somewhat similar history was 
that of female 378 described earlier in the section 
(p. 27) titled “History of a Typical Burrow during 
its First Week.” 
There were nine females born during 1948 for 
whom the fate of the first litter was known (see 
table 32). All of these females conceived and 
reared a second litter except female 92. She did 
not again conceive. Those rats which reared their 
first litter exhibited a more favorable pattern of 
growth, as indicated by their maturity index rating. 
They also were born earlier in the breeding season, 
when their was less opportunity for stress resulting 
from competition with more associates. This pro- 
vides further evidence that the degree of maternal 
care is negatively correlated with the intensity of 
social interaction. 
Table 32 . — Characteristics of 9 females born during 1948 for whom the fate of the first litter was known 
Rat No. 
Mean 
maturity 
index 
Date of birth (1948) 
Place of birth 
92 
I. 36 
April 17 
Area I. 
Reared first litter 
96 
I. 17 
.... do 
Area I. 
75 
I. 00 
March 16 
South Alley Burrow. 
80 
1.07 
.... do 
South Alley Burrow. 
48 
I. 19 
March 21 
Area II. 
378 
II. 17 
Sept 
South Alley Burrow. 
Did not rear first litter 
697 
I. 50 
May 18 
South Alley Burrow. 
702 
II. 00 
.... do 
South Alley Burrow. 
733 
I. 50 
July l 
Area I. 
B. Some Case Histories of Mother to Young Relation- 
ships. Litters were most frequently born in burrows 
or were transported there from an adjoining har- 
borage box shortly after birth. Few observations 
were possible under such circumstances. However, 
there are three groups of data which are sufficiently 
detailed to present a better comprehension of the 
life of the young rat than is gained from the presen- 
tation of more isolated records. 
a. Litter 2. This litter was born on April 16, 
1947, at the recently constructed South Alley Bur- 
row, and represented the first successful litter born 
in the pen to the introduced rats. On the night of 
April 30-May 1 there occurred a rainstorm which 
innundated the burrow, and forced the mother, No. 
10, to transport her young to a drier location, Box 
36, in which there was already a nest. My first 
awareness of this incident was during the morning 
of May 1 after the sun was well up. The mother 
was observed in the process of transporting the first 
of the six well-furred young, with eyes still closed, 
back to the home burrow. After a quick examina- 
tion of the remaining five young in Box 36, I left the 
pen in order not to further disturb the mother in 
this process of transportation. 
144 
