SOCIAL MODIFICATION OF PERIODICITY OF ACTIVITY 
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Figure 
SOCIAL 
RANK 
LOW 
HIGH 
PASSAGE USED 
INTO FOOD PEN 
5-POINT MOVING 
AVERAGE 
TREND 
NORTH (NO. 7 ) • 
SOUTH (NO. 5) □ 
(WITH PHASE OF MOON INDICATED) 
1947 
1948 
19 29 
MARCH 
17 27 
MARCH 
8 19 28 8 18 28 7 5 15 25 
APRIL MAY JUNE FEBRUARY 
1948 1949 
93. — Social modification of periodicity of activity. Five-point moving average of the percentage of post midnight 
activity. With few exceptions the lower ranking rats showed relatively more activity after midnight. 
that when there are moonlight nights the rats must 
be active for at least a portion of the night in order 
to meet their nutritional requirements. This 
activity occurs during the first half of the night 
when their hunger and thirst drives are at a 
maximum. Coincident with the reduction of the 
hunger and thirst drives the light from the full 
moon is enabled to exert its full inhibitory effect 
upon activity. As the new moon phase approaches, 
the inhibitory effects of increased light intensity 
during the night declines and so postmidnight 
activity again increases. 
For the remainder of the data this lunar peri- 
odicity of activity was either completely absent or 
out of phase with the moon itself. However, in 
the light of complicating social events which 
occurred after January 1948 this was not at all 
surprising. It will be recalled that the period of 
November 1947 through January 1948 was the 
time of minimal social tension. During the period 
of minimal social tension, we must assume that the 
lunar periodicity of activity had become endoge- 
nous. As the onset of the 1948 breeding season 
occurred the increased activity associated with 
sexual behavior prevented (he decline in postmid- 
night activity that would have occurred about 
February 24. Following this, the maintained level 
of increased social tension reduced the amplitude of 
120 
