Figures 1 5 to 20. — The development of the surface appearance of the South Alley Burrow from April 22, 1947, to May 7, 
1949. The section of the burrow about passage 1 developed as an offshoot from the main burrow but later became 
severed from it. The entries of these two sections of the burrow are numbered independently according to the chronological 
order of appearance in each. The position of the initial entry is indicated by a plus mark. See figure 4 for photograph 
of burrow in April 1948. 
SOUTH ALLEY 
BURROW 
APRIL 22, 1947 
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B. 
MOUND AND OPENINGS 
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There were two adjuncts to this decay of or- 
ganization of the burrow, both of which are sus- 
pected to be causally related to this decay. The 
first of these was the social organization of the 
group inhabiting the North Alley Burrow. This 
organization was one characterized by an in- 
stability of interindividual relationships and low 
social rank of the members with reference to the 
colony as a whole (see pages 210 to 212). The 
second was the contact of an underground tunnel 
with the barrier fence during the summer of 1948. 
Once this happened there was a rapid develop- 
ment of the burrow along the fence with a con- 
comitant shift of focus of activity away from the 
older more organized portion of the burrow. 
The tunnel systems discussed above and il- 
lustrated in figures 21 and 22 represent burrows 
which were intensively used by many rats over a 
long period of time. A large number of smaller 
burrows was excavated both within the experi- 
mental pen and at various locations through 
Baltimore County. Two typical, more youthful 
burrows are shown in figure 23. The left-hand 
figure, Burrow Study 2, Site 1, illustrates the pat- 
tern which soon arises when the burrow is initiated 
in a plot of ground away from barriers, such as 
fences, or other objects toward which the rat might 
direct its burrow construction. This pattern is 
one of a single point of excavation, two entrances, 
several nest or food storage chambers, and a 
circular system of communication. The right- 
hand figure depicts how the development of a 
burrow may be soon modified by surrounding 
structures. This Area II Burrow 2 began along 
the outer barrier fence. The edge of the left hand 
mound is parallel with the fence as is also the 
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