80 % 
LENGTH OF TUNNEL SEGMENTS IN mm 
Figure 44. — Lengths of tunnel segments. Note that the great majority of the tunnel segments are no longer than the total 
length of an adult rat. 
distance. If it did not, / would approach — > 
the second curve shown in figure 45, which does 
not fit the data. Our problem then resolves itself 
into the consideration of the contribution to the 
variability in W. 
W=Ce-=0[ 1+z+fh^ 
where n!=l • 2 • 3 . . . n 
Each of the succeeding factors in this equation 
represents the effort required by behaviors which 
are brought into play as the tunnel becomes longer- 
C may be designated as the work involved in the 
decision to begin excavating a tunnel. 
CX may be designated as the work involved in 
excavating the dirt from the surface at the end of 
the tunnel, irrespective of its transportation. CX 
will be directly proportional to the length of the 
tunnel. 
x* 
C-y> the primary transportation factor, may 
not be designated quite so simply. However, 
the following logic will show the nature of this 
factor: Let us suppose that rats A and B each dig 
a tunnel of the same length (d/2). After finishing 
this tunnel each again constructs another tunnel 
of similar length. Rat A makes this second tunnel 
a continuation of the first. This means that any 
dirt excavated from the second tunnel must be 
carried back through the first tunnel to be deposited 
on the ground. However, Rat B initiates his 
second period of work at the surface of the earth 
and so has a much shorter distance to transport 
the dirt (see fig. 46). In other words, the longer a 
45 
