activity records are available, there were wide fluc- 
tuations of both increase and decrease in activity 
from a day immediately preceding or following it, 
but on which no precipitation fell. The median 
change in activity on the night of rainfall was exactly 
zero percent. 
During nine of these nights 0.4 or more inches 
of rain fell within 12 hours or less. In four of these 
cases there was significantly less activity during the 
time of rain than during a similar period of the ad- 
joining day when it was not raining. On the other 
hand on 2 days there was significantly more activity 
during the rain. There is a basic criticism of this 
data. This is that the metal tunnels which housed 
the activity recorders, probably attracted the rats 
as a place of escaping downpours. This would tend 
to increase the number of closures of the photo- 
electric cell while it was raining. For this reason, 
I am inclined to place greater weight on the fol- 
lowing more qualitative observations as reflecting 
the effect of rain upon rats. 
September 15, 1947: Traps were set last night 
but no rats were caught. It rained hard all 
night. The traps were left set during the day. 
By 5 p.m. 6 of the 29 rats in the pen had been caught 
in traps during the day after 9 a.m. 
October 5, 1948, 5:30 to 6 p.m. Raining and 
high wind: By 5:45 p.m. there were at least 20 
rats at a time in the Food Pen. Their activity 
was confined to eating and drinking. Although 
there were avoidances between rats, there were no 
fights. In other parts of the pen activity consisted 
of running rapidly between burrows, harborage 
boxes, and the Food Pen. It appears as though 
the rain inhibited extraneous activities such as 
sexual, fighting, or investigatory, and restricted 
them to the essential ones relating to ingestion. 
September 9, 1948, 6 to 6:30 p.m. Raining 
steadily. There is a much smaller proportion of 
the total rats out than is usually observed at this 
time of day. Although there seems to be a tend- 
ency to engage in less wandering activity, the rats 
which are out appear to pay little attention to the 
rain, and one male even engaged in a sexual roll 
at a burrow entrance. 
D. Effect of Snow on the Amount of Above Ground 
Activity. During the history of the colony numerous 
surveys were made of the distribution of feces. The 
general conclusion from these surveys was that the 
number of feces at any one point was a reflection 
of the frequency with which the rats visited that 
place. The data for June 5, 1947, will serve as a 
basis for comparison when the weather was mild 
and without snow. On this date there were 22 
rats in the pen. On this date a count was made 
of the feces which were still sufficiently fresh and 
glistening from contained moisture to indicate that 
they had been deposited within the previous 2 
nights (see table 24). This gives a mean of 6.75 
Table 24. — Feces recorded on the June 5, 1947 , survey 
Place of deposition 
Number of 
feces 
On surface in areas 
96 
In boxes in areas 
44 
On surface in alleys 
95 
In burrows in alleys 
*44 
In food pen 
18 
Total 
297 
*The estimate of the number of feces deposited in the 
burrows was made on the assumption that the belowground 
and aboveground feces in the alleys was in the same propor- 
tion as in the areas. 
feces per rat per day, and a mean of 4.75 above- 
ground feces per rat per day. 2.38 times as many 
feces were deposited above ground as below ground. 
On January 31, 1948, when there were 25 rats in 
the pen, a survey of the aboveground feces was 
made. During the previous 5 nights the tempera- 
ture was continuously below freezing and the sur- 
face was covered with snow. During these 5 days 
there was a total of only 96 feces deposited on the 
surface of the snow. Thus, there was less than one 
aboveground fecal bolus per rat per day deposited 
during this period (see table 25). 
Table 25. — Feces per rat per day 
Above 
Below 
Percentage of 
Date 
ground 
ground 
total defecation 
on surface 
June 5, 1947 
4. 75 
2. 00 
70 
Jan. 31, 1948 .... 
.77 
*5. 98 
11 
*The belowground estimate is based on the assumption 
that the mean number of feces per rat per day was the 
same for the two periods. 
131 
