ECOLOGY OP ISLE ROYALE. 4C3 



for a detailed account of the habits and activities of this animal, has 

 become a classic in American natural history. 



In brief the life history is as follows : The breeding season, according 

 to MacFarlane ('05, p. 742), occurs in January and February, at which 

 time the males light fiercely. The young, blind at birth, are born during 

 April and May, and are suckled for several weeks, but soon begin to eat 

 the succulent stems and roots of plants. The young are believed to 

 remain with parents for 2 or 3 years, and to breed at about the age of 

 three. They are most prolific at about middle age, when they usually 

 produce from 4 to 6 at a birth, and occasionally even 8 or 9. The 

 Indians believe that they reach the age of 12 to 15 years (Morgan, '68, 

 p. 222). There is a tendency for beavers to migrate (Morgan, '68, p. 

 137), especially when a region becomes overstocked, and very naturally 

 they follow the streams. 



Their food consists of roots of grasses and water plants, including the 

 water-lily, the bark of aspens, fresh willow branches, birch, the leaves 

 of deciduous trees, and late in winter even of wood itself. The winter 

 supply of food is stored under water. The burrows, lodges, dams, and 

 meadows that result from the activities of this animal have aroused 

 much piopular interest, but space can not be allowed to describe 

 these in detail. There is a very extensive literature devoted to this 

 phase of beaver life. The Beaver is essentially a burrowing animal, so 

 that the margins of the waters which they frequent contain numerous 

 burrows or tunnels. These are from 10 to 15 feet long and open, at the 

 lower end, a foot or so below the water; from this point they incline 

 upward to within a few inches of the surface of the ground, thus allow- 

 ing for the necessary ventilation of the burrow. Morgan reports that 

 in the case of the river-inhabiting beavers the upper ends of these 

 tunnels are occasionally indicated by a pile of cuttings a foot or so 

 high, and that it is probable that from such a beginning as this beaver 

 lodges have been developed. Of these lodges there are several modi- 

 fications, but their essential features are a burrow with submerged en- 

 trance, which leads upward into a chamber above the surface of the 

 water. As a rule these lodges are located on the bank a few feet back 

 from the water, but they also occur at the margins of streams or lakes. 

 and within the ponds made by the dams. It is very evident that all of 

 these lodges are but variations of the same fundamental plan. 



The beaver dams excite much interest, and the completed dams may 

 be quite extensive affairs as some are even several hundred feet long and 

 over 6 feet high, causing the submergence of many acres of land. But 

 it should be borne in mind that such feats are not the work of a single 

 pair or family, but are the results of generations of industrious beavers. 

 These dams are begun on a small scale, in all probability by a single 

 pair or family, and in the course of time each generation contributes its 

 share toward the repair and extension of the dam, so that in time it 

 may become a very composite structure and perhaps of great extent. 

 The dams, like the burrows and lodges, are built upon a simple plan, 

 and susceptible of much modification in different conditions. Thus on 

 small streams according to Morgan, where the banks are ill defined, the 

 usual form of dam is one composed of sticks and poles, whose upper 

 or water face is reinforced and plastered over with earth, stones and 



