3n 



walls and increases the warmth of the house, but 

 also freezes and becomes an armor of stone that 

 is impregnable to most beaver enemies. The 

 " mudding " of the house is a part of the natural 

 and necessary preparation for winter. It may also 

 be a special means of protection deliberately car- 

 ried out by the beaver. The fact that an occa- 

 sional thick-walled or grass-covered beaver house 

 was not thus plastered in autumn perhaps be- 

 cause it did not need it has led a few people 

 to affirm that beaver houses are not mud-covered 

 in the autumn. Many years of observation show 

 that most beaver houses do receive an autumnal 

 plastering, and the few that do not have this at- 

 tention usually have thick, well-preserved walls 

 and do not need it. 



One autumn in Montana, of twenty-seven 

 beaver houses which I examined, twenty-one re- 

 ceived mud covering; three of the others were 

 thickly overgrown with willows and two were 

 grass-grown. Only one thin-walled house that 

 needed reinforcement did not receive it; and this 

 one, by the way, was broken into by a bear before 

 the winter had got fairly under way. 



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