on 



considered by beaver before beginning dam- 

 building, the supply of food and of dam-build- 

 ing material, for instance, and the location of 

 the dam so as to require the minimum amount of 

 material and insure the creation of the largest 

 reservoir. In making the dam, the beaver usually 

 takes advantage of boulders, willow-clumps, and 

 surface irregularities. But he often makes errors 

 of judgment. I have seen him abandon dams 

 both before and after completion. The apparent 

 reasons were that the dam either had failed or 

 would fail to flood the area which he needed 

 or desired flooded. His endeavors are not always 

 successful. About twenty years ago, near Helena, 

 Montana, a number of beaver made an auda- 

 cious attempt to dam the Missouri River. After 

 long and persistent effort, however, they gave it 

 up. The beaver may be credited with errors, 

 failures, and successes. He has forethought. If a 

 colony of beaver be turned loose upon a three- 

 mile tree-lined brook in the wilds and left un- 

 disturbed for a season, or until they have had 

 time to select a site and locate themselves to best 

 advantage, it is probable that the location chosen 



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