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Figure 36. — Sealing of an opening into a burrow with vegetation. On the night of November 24, 1948, the roof of a nest 
cavity in the mound of the North Alley Burrow caved in. The rats climbed the neighboring small pine trees where they 
cut fascicles of needles and with them covered the opening. Presumably this behavior has the result of reducing air drafts 
into the burrow or in preventing the entry of other rats. 
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