13. Male 12 
14. Male 12 
15. Male 12 
16. Females 17 and 20 (sibs) 
17. Females 20 and 25 (sibs) 
18. Spring of 1949 
5:20 to 5:40 a.m. and 7:22 to 7:26 p.m.; May 17, 1948; 635 days of age 
Male 12 is now way down on the social scale. He was observed eating during 
these two periods when most other rats were inactive. 
2:00 to 2:15 p.m.; October 7, 1948; 778 days of age. With one other 
adult rat eating; few other rats active. This is another observation which 
shows that low ranking rats come out early to eat. After becoming senescent 
male 12 dropped from the top to nearly the bottom of the social scale. 
6:43 a.m.; October 8, 1948; 779 days of age. Now that all other rats have 
entered their burrows Male 12 has returned to the Food Pen. He was 
cautious even so and took the pellet of food to the northeast corner of the 
Food Pen to eat. 
May 17, 1948; 350 days of age. They ate in the Food Pen together after 
the dominant rats retired. They then returned to approximately the same 
place of harborage. 
5:05 to 6 a.m.; May 24, 1948; 357 days of age. Both rats are wandering 
about the Food Pen. This is further evidence that the social outcasts are 
forced to eat during times when other rats are inactive. 
It has been a general observation that rats seen at the food source late in 
the morning or early in the evening were those with extensive wounds or 
poor pelage. 
These and similar observations may be summar- 
ized as follows: All of the rats in the population 
were not simultaneously active. During the after- 
noon and early dusk a few of the socially lowest 
ranking rats visited the food source. As these re- 
tired to their harborages the socially high-ranking 
rats (in general those rats living in the south half 
of the pen) became active. It was usually not 
until these higher ranking rats had begun to de- 
crease the frequency of their visits to the Food Pen 
that the majority of the lower ranking rats (in gen- 
eral those rats living in the north half of the pen 
emerged from their burrows and began visiting 
the food source. This social stratification of period- 
icity tended to be maintained through the night 
with the lower ranking rats seeking access to food 
during times of maximum quiescence of the re- 
mainder. Through such a process of social strati- 
fication of periodicity of activity strife between 
members of different groups was reduced but by 
no means eliminated. It seemed patent that the 
degree to which a rat had to modify its normal 
rhythms of activity and quiescence was a direct 
reflection of the degree of stress to which it was 
exposed. Since 20 rats appeared to be about the 
upper limit of numbers that were tolerated simul- 
taneously in the Food Pen, it is apparent that as the 
population increased from one-half to nearly 10 
times this limit, all individuals must have been ex- 
posed to increased stress through social action, 
because at the higher densities it would be nearly 
impossible for different groups of rats to time their 
activities so that there would not be considerable 
overlap. 
135 
