Figure 62. — Rat trail down path 3 from the north corner of the Food Pen to tile passage 3 through the median barrier fence, 
November 23, 1948. Note how the rats have worn a narrow trail down the middle of the 3-foot wide cleared path. 
The lightness of the path is due to a profuse growth of microscopic plants, cultured on the urine-and-feces-enriched soil. 
This illustrates the fact that even when rats cross bare, open spaces, they adhere to a restricted zone of travel. 
trail through the vegetation also resulted from 
similar orientations toward vertical objects. 
On January 24, 1948, 5 inches of snow fell 
between 8 a.m. and 6 p.m. The majority of the 
snow fell before the rats became active. It obliter- 
ated the trails existing over previously fallen snow. 
Even so, the rats again developed a trail (see fig. 
6511) with essentially the same orientations to the 
tree trunks. Such a trail is shown in figures 66 
and 67. 
The subnivean trail shown in figure 65E is 
discussed in more detail elsewhere (pp. 74 to 78). 
Although the point-to-point orientation is apparent 
in this figure, the visual orientation to vertical 
cues was no longer possible. Once the rats make 
contact with one vertical cue they must have 
64 
