Yellozvstone Beaver 215 



the animals do, however, when the trees are at a distance from the 

 shore, and the ground is flat enough to permit of carrying water in 

 on a level, or controlling it by miniature dams. These ditches vary 

 in width from 1 to 4 feet, in depth from 8 inches to 2 

 feet, and the length may be but a few feet or very much more. 

 Morgan mentions two in Michigan 523 and 579 feet long respec- 

 tively. There is one on Tower Creek 90 feet long, and another 150 

 feet. Where the slope of the ground is such that the water would 

 not maintain its level in the canal, a small dam is built to hold it 

 back. Thus one of the Tower Creek canals was 17 feet long at 

 the pond level from the shore to the lower end of the dam, and 23 

 feet to the upper side of the dam, and above this was another section 

 of ditch 64 feet long (figure 65). The lower level of course 

 obtained its water from the pond and was 15 inches deep (figure 66). 

 The upper level was 9 inches deep and was supplied by drainage 

 from the marshy ground about it. The canal was from 15 to 18 

 inches wide. The difference in level between the two parts was 

 20 inches. The long, gradual slope of the lower face of the dam 

 facilitated dragging logs over it. 



The other canal on Tower Creek was about half a mile up the 

 creek from the preceding (figure 67). It was connected with the 

 stream by a trail 23 feet long, and at the time of the examination 

 this was 2 feet above the water level. This canal was from 3 

 to 4 feet wide, and 12 to 18 inches deep. The westerly bank was 

 considerably lower than the other, and was being raised by mud dug 

 from the bottom. The water supply was apparently derived from 

 a spring at the landward end. 



Life History, Other Habits, and Enemies 

 The number of young in a litter is from two to five, three or four 

 being probably most common. They are born during May. I have 

 not been able to learn at what time they first make their appearance 

 outside the home nest ; but most writers state that they appear in a 

 very few weeks. At Camp Roosevelt I was sure there must be a 

 family in the lodge in one of the ponds on the Cooke City road. 

 There were two adults (figures 69, 70) and three yearlings seen 

 almost every evening, but no smaller animals. I looked for them 

 on my frequent visits, but it was not until August 22 that the young 

 were seen, three, as large as big muskrats. Having a close look at 

 one, I estimated its length as eighteen inches, while the yearlings 



