Figure 53. — Nest made entirely of leafless sections of honeysuckle vine. The lining is of oak leaves. Nests are frequently 
lined with leaves, although paper may be similarly used when it is available. 
lid of the harborage box, she would frequently 
build a nest at another location and transport her 
young there. The young often disappeared follow- 
ing this minimum disturbance, so it is assumed 
that the mother destroyed them. On two occasions 
the young of primiparous females were found on 
old pad nests. The infrequency with which 
primiparous females reared their young is perhaps 
associated with the poor development of the nest- 
building behavior and allied maternal behaviors. 
There are two other closely related behaviors 
exhibited by females with young. The first of 
these is the covering of the young with nesting 
material. On two occasions females were ob- 
served nursing young in cup-shaped nests lacking 
hoods. Upon reexamination of the nest within 2 
hours the mother was absent and the surface of the 
nest was flat with the young not visible. In each 
case the young were found in the nest depression 
when this covering material was removed. The 
second behavior was that of sealing the lid with 
mud (p. 42). 
2 . Trails, Orientation, and the Utilization 
of Space 
A. The Growth of Trails in the Experimental Pen. 
Rats usually confine their movements to the same 
routes through the same localities day after day. 
Resultant trails may even be detected over bare 
ground. More frequently the trails lead through 
vegetation. This vegetation is kept cleared from 
the floor of the trail, although it may form an arch 
overhead. 
Even before the initial colonizers had the op- 
portunity of increasing their numbers through 
reproduction a few trails began to appear (see 
fig. 59 A for May 1947). At this early stage the 
54 
