THE WILD LIFE OF LAKE SUPERIOR 



191 



Photograph by George Shiras, 3d 

 A COMPLETED MUSKRAT HOUSE (SEE AESO ILLUSTRATION ON OPPOSITE PAGE) 

 This flashlight shows the pair of muskrats putting the finishing touches to their home. 



suppose that the beaver primarily de- 

 pends on bark, and that such soft vege- 

 tation as it feeds upon is incidental and 

 irregular. This is an error, for the 

 beaver in its extensive ranges relies upon 

 bark only during the months when other 

 food cannot be easily obtained or stored. 

 By adaptation to the seasonal food sup- 

 ply, the beaver resorts to the more perish- 

 able aquatic growths from May to Octo- 

 ber, and to the many varieties of land 

 plants, bushes, and vines, thereby con- 

 serving the arboreal supply for a time 

 when the deciduous plants yield to the 

 frosts or gradually chilling waters. In 

 higher altitudes, where spring or glacial 

 streams are often too cold for vegetation, 

 the beaver depends upon bank willows, 

 weeds, and the other small growths, 

 though occasionally the bark of poplars 

 or birch is eaten at the base, the tree sel- 

 dom being cut before fall. 



Prior to 1700 the beaver was seldom 

 molested by the Indians of the upper 

 lakes ; for, aside from decorative pur- 

 poses, they preferred larger skins for 

 domestic use. 



The early explorers found the usual 

 meadows and alder-covered flats, where 

 the original forests had been killed by 

 the flooding caused by beaver dams ; but, 

 as the watercourses were fringed almost 

 entirely with conifers, the lake region in 

 the beginning was not a particularly good 

 beaver country. When the aquatic plants, 

 willows, alders, and black ash, constitut- 

 ing their principal diet, became exhausted, 

 the animals migrated elsewhere, and thus 

 these cycles of occupation and abandon- 

 ment were regulated entirely by the ques- 

 tion of food. 



On the arrival of the trappers it did 

 not take long to reduce these numerous 

 but scattered colonies, and for a hundred 



