of intervening barrier fences; 2. The shortest 
distance between the place of birth and the place 
of later capture with respect to the distance which 
the rat must actually travel around barriers be- 
tween the two points. Both of these two ways of 
examining the distribution are shown in figure 
117. For both plottings, the general conclusion 
of decreased frequency of captures at increased 
distances remains valid. However, only the dis- 
tribution of distances across barriers (table 39B) 
presents a consistent pattern of decrease. The 
conclusion is therefore drawn that the rats main- 
tain their orientation to the site of birth with 
reference to actual, rather than to “locomotor” 
distance. 
If this is really a valid conclusion, and the data 
indicate that it is, the question then arises as to 
how such orientation is maintained. In the first 
place, we may exclude the contention that the 
orientation is a spurious one resulting from the 
chance dispersion of the rats, for were this so, we 
might have anticipated a consistent decrease in 
the frequencies of distances around barriers. 
Therefore, we must conclude that the orientation 
is real, and furthermore, that the place of birth 
holds a permanent attraction for the rat. Since 
the places of capture represent for the most part 
actual or approximate places of residence, the rat 
must be able to detect both the direction toward 
and the distance from the place of birth. The 
observations were not amenable to offering any 
definite proof of the means of perception of the 
site of birth from points removed from it. How- 
ever, the existing conditions suggest possible means. 
In the first place, the barrier fences, though 
barriers to locomotion, were not barriers to vision. 
Even so, considering the fact that most orientation 
occurred during hours of low light intensity, and 
that intervening vegetation must have precluded 
visual observation by the rat for any appreciable 
distance, it is concluded that vision was not the 
primary means of perception of the site of birth. 
I am inclined to suspect that the perception 
involved is that of hearing the vocalizations of 
those rats which are residing at the site of birth. 
It is quite certain that a rat in one portion of the 
pen can respond to the vocalization of a rat in 
another part. The fact that a rat as an adult is 
not residing at its place of birth is mainly attributa- 
ble to social action from other rats which produced 
its exclusion. Therefore, the final postulate is 
that a rat is able to recognize the particular 
vocalizations of one group of rats in contrast 
to that of all others. 
The extent of the home range of the introduced 
rats was in general much greater than that of rats 
born in the pen. There were three major contrib- 
uting conditions to this greater extent of home 
range. 1. The initial training period, February 13 
to March 14, 1947, was such as to force all the rats 
Figure 117. — Distance of place of birth to places of later capture. The distance tQ each place of capture was measured in 
two ways. 1 . across barriers such as fences in a straight line from the place of birth; 2. around barriers along the shortest 
route a rat would have to travel from its place of birth. In (A) straight lines have been fitted empirically to the points. 
These same lines were reproduced in (B) for comparison. 
676-768 O — 63 12 
169 
