conditions of the weather with reference to the 
decay of the feces probably introduced so great an 
error as to preclude any usefulness of such counts. 
The conclusion is therefore, made that in the sign 
estimation of population density, the presence of 
feces must remain as a rough qualitative index. 
With the exception of the very few observations 
of wet spots along trails, etc., which appeared to 
be distributed much as were feces, I have very 
little direct information regarding urination be- 
havior. However, rats were frequently observed 
to rub their bodies against passages through fences, 
tile entries into harborage boxes, or over clods of 
dirt, rocks, or the entries to burrows. Defecation 
does not occur during this activity. It is assumed 
that some urination actually occurs during this 
rubbing process or that scent passed out with the 
urine and adhering to the fur is rubbed off. De- 
tails of this behavior are presented in the discussion 
(pp. 152 to 158) of sexual behavior of which it 
forms a component part. That the scent leaves 
the body with either the feces or urine is shown by 
the following. The feces and dried urine accumu- 
lating in the tray under the cage of a laboratory 
strain of the Norway rat was preserved by washing 
the tray with 50 percent alcohol. When this solu- 
tion was poured over objects in the pen and allowed 
to dry it attracted the wild rats and elicited from 
them similar but somewhat more intense inspection 
and sexual behavior than normally followed the 
leaving of such sign by one of the rats in the pen. 
Such activity by the rats in the pen served to form 
sign posts which attracted the presence of other 
rats. 
Urine and feces adhering to the feet of rats be- 
comes spread along trails. This serves to support 
a rich algal growth to the extent that the trails 
stand out as shown in figure 62. 
6 . Activity 
A. Fluctuations in Intensity and Periodicity of Loco- 
motor Activity. Even the most casual observation 
of wild rats reveals that they tend to be nocturnal. 
1 lowever, when ources of food, such as garbage 
about homes or food for domestic animals, are 
temporarily available only during the day hours, 
rats readily adapt to these situations and exhibit 
an increase in diurnal activity sufficient to insure 
adequate use of these temporary sources of food. 
In the preparation of sign surveys of rats in city 
blocks one also gets the impression that meteoro- 
logical conditions affect the amount of above- 
ground activity. At the beginning of this study of 
the rats in the pen, I held few preconceived notions 
regarding specific ways in which surrounding 
conditions might alter periodicity or intensity of 
activity. The following discussions summarize the 
results of analyses of these observations. 
An objective measure of intensity of activity was 
obtained through the utilization of photoelectric 
cells placed within a protected hood (see fig. 63 
and 76) at each of the passages through the Food 
Pen fence. Upon the breaking of a beam of light 
to the photoelectric cell by the passage of a rat, a 
pen was activated to make a mark on a strip of 
paper moving at the rate of 1 foot per hour. Each 
mark on the tape was designated as a unit of 
activity. There was a separate pen for each of the 
four passages. Although activity was measured 
only in terms of movement in and out of the Food 
Pen, it was observed that whenever a particular 
group of rats emerged from their harborages at 
least a portion of them were involved in the move- 
ment in and out of the Food Pen. In fact, the 
general impression was gained that the total above- 
ground activity was proportional to the activity 
in the Food Pen. 
We shall first examine a sequence of records of 
the distribution of activity through the 24-hour 
period (figs. 81 to 90). In each figure there was 
represented what might be designated as the general 
pattern of the 24-hour rhythm. Each of these 
general patterns was determined by obtaining the 
percentage of activity which occurred during each 
half-hour interval over a period of 10 days. With 
each such general pattern there is given as contrast 
the rhythm of activity for 2 separate days. The 
activity cycle for a particular day is often quite 
different from the general pattern resulting from 
lumping the data for a series of days. 
As a background for some of the interpretations 
that will be given to these figures, it will be neces- 
sary to consider some of the experimental work on 
activity rhythms in laboratory strains of the Norway 
rat. A review of rhythms in the Norway rat is 
covered in pages 373-378 (1945), and 208-209 
(1946) in a general review of 24-hour periodicities 
in the animal kingdom (13). The following excerpt 
suffices for the present interpretations: 
“The pioneering work of Slonaker (1907) on 
the white rat is the first thorough study on the diel 
(24-hour) activity cycle of a mammal. In this 
and his later (1912) study, adult rats showed a 
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