1. Growth and life span of the individual. 
2. Reaction of the rats to the physical compo- 
nents of the environment. 
a. Orientation responses to those components 
of the environment which serve as cues. 
b. The effect of meteorological conditions and 
related factors which may alter intensity or 
periodicity of activity. 
3. Investigation of population dynamics irrespec- 
tive of the social factor. 
4. Systematic recording of all types of behaviors 
and other variables with the expectation that 
these might lead to a better understanding of 
the rat as a species. 
5 . Experimental Procedure and the Gathering 
of Data 
Once the colony was initiated, every effort was 
made to interfere as little as possible with the daily 
routine of life which the rats established. It was in- 
tended that such changes as might occur in the 
colony should be brought about by the activity of 
the rats themselves. 
Observational techniques: The objective was estab- 
lished that, in so far as possible, all observations 
should pertain to known individuals and not to just 
rats in general. This required the permanent 
marking of individuals so that whenever handled 
each rat could be recognized, and it required the 
occasional marking of individuals so that they could 
be recognized at a distance without hampering 
their normal activities. The former was accom- 
plished by inserting numbered light weight alloy 
fingerling fish tags in the ear lobes of the rats. It 
was found advisable to place a tag in each ear since 
occasionally the ear would become infected and the 
tag lost. Since two tags were rarely ever simultane- 
ously lost, it was possible through this procedure to 
maintain a continuous identification of the indi- 
vidual. The tags utilized were obtained from the 
National Band and Tag Company, Newport, Ky. 
I have also used with success on other rodents simi- 
lar tags produced by the Salt Lake Stamp Co., 43 
West Broadway, Salt Lake City 1, Utah. The 
problem of sight identification was finally solved 
by using a commercial cosmetic depilatory, Nair. 
Spots of hair could be removed from the locations 
shown in figures 8 and 9. Sexes were differentiated 
by removing the hair from the top of the head on 
females. During the warmer months of the year, 
when the testes were descended into the scrotum, 
PELAGE MARKING CODE 
Figure 8. — Code for the pelage marking of rats. The pelage 
was removed from no more than two locations on a single 
rat. Sexes were indicated by removing a spot from the 
head of the female. See figure 9 as an example of 
marking. 
males could be distinguished by this character ir- 
respective of pelage marking. It was found ad- 
visable never to remove more than two spots on a 
single animal (other than on the head). This 
pelage marking system provided 43 combinations 
for each sex (table 1). 
The rat is quite a nocturnal animal. This 
presented a problem in making adequate observa- 
tions. Fortunately, there was considerable activity 
during at least the half-hour before sunset. Even 
after sunset there was sufficient light to permit 
676-768 O — 63 2 
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