Figure 58. — Heat production by large aggregates of rats. The bare tops of boxes 30 and 31 may be seen in the upper right 
of the photograph. See also figure 33. At least 33 rats were housed in and moved between these 2 harborage boxes. 
The heat produced by these aggregates was sufficient to pass through the 1 1/2 inches of wood and insulation board and 
melt a several inch covering of snow. Approximately 60 rats were using the mudstained trail to the right on this date, 
December 21, 1948. As was the case prior to the snowfall, the trails connect passages into burrow systems, into har- 
borage boxes, or through barrier fences. Such passages into harborages were primary goals in spatial orientation. 
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