Figure 69. — Initial orientation through a clump of vertical cues after a 5-inch snow. The goldenrod stalks in the upper right 
corner are that half of the clump shown in figure 68, which is nearest passage 1. When the trail is obscured by such a 
snow, rats are unable to duplicate a curved trail through closely spaced groups of vertical cues. Neither of the bifurcated 
trails duplicated the underlying trail. During the next two nights a single trail developed through this area slightly to 
the south of the original trail. 
a curved trail. During the following two nights 
the rats concentrated their activities over two of 
the most peripheral of this aggregate of trails. 
b. Orientation under snow. The 5 inches of snow 
which fell on January 24, 1948, lasted for 11 days 
without further addition of new snow. The 
severeness of the weather prevented this from 
melting significantly although there was a com- 
pacting of the snow until it formed an ice crusted 
layer 2 to 4 inches deep. Over this the rats 
confined their travel essentially to the routes shown 
by the dashed lines in figure 71. 
At 6 a.m. of February 4, 1948, it began to snow 
and continued steadily snowing for the following 
18 hours until an average depth of 10 inches of 
new snow had fallen. On the morning of Febru- 
ary 5 I climbed the tower for a preliminary survey 
before entering the pen in order to determine the 
reaction of the rats to this deep snow. The snow 
was completely unmarred and so 1 initially as- 
7 4 
