BEAVER FAMILY 



213 



traded the most attention. A fairly narrow valley 

 is selected through which flows a small stream 

 with a slowly moving current. Across tliis a 

 dam is made of sticks, stones, mud and ruhbish. 

 The dam is usually from four to six feet high, 

 eight to sixteen feet broad at the base and a 

 foot or two wide at the top. The length may 

 vary from a few feet to several hundred. The 

 longest observed by the writer is in Estes Park, 

 and is 1040 feet long. Above it and below it 

 are series of shorter dams. These structures are 

 by no means always convex upstream, as some 

 of the older writers assert, but often bend down 

 stream, and the longer ones are frequently zig- 

 zag. Secondary dams are often built below the 

 first. These are apparently for the sole purpose 



together by vegetation. Strong as they are these 

 dams are often broken by flooded streams, but 

 arc quickly repaired by the ever watchful 

 builders. 



Structures which cost so much work as these 

 must be of much value to the Beaver. Two pur- 

 poses are fvilfilled. Usually the dam forms a 

 pond deep enough so that the openings into 

 the Beaver houses, or into burrows in the 

 bank, are far enough under water to pro- 

 tect their owners against enemies. The center of 

 the pond provides a storage place for the large 

 supply of green sticks collected for the winter 

 food. A third use is to extend a body of water 

 toward a group of trees which the animals are 

 to cut and float to their homes. 



Photograph by C. Reid 



BEAVER SWIMMING 



of backing uj) the water against the first dam, 

 and so relieving the pressure — an astonishing 

 proof of the animal's intelligence. 



In making the dam mud is used, reinforced 

 by sticks from four to twenty feet long, and 

 from two to six inches in diameter. These are 

 laid approximately parallel to the stream flow, 

 with the larger ends upstream. They are held 

 in place by piling mud and stones on these ends. 

 More sticks are piled above the first and so on 

 until the required height is reached. The mud 

 is taken from in front of the dam and deepens 

 ■-the water at that point. Sometimes simply a 

 barrier of sticks is made through which the water 

 passes freely. In the course of time, however, 

 floating material lodges against the sticks and 

 completes the dam. 



As time goes on the sticks decay ; more and 

 more mud is added by the Beaver ; grass, willows 

 and alders get a strong foothold and we have a 

 solid structure of earth and rocks held firmly 



As has been indicated, Beavers live in houses 

 or in holes in the banks of ponds. The houses 

 are made of much the same materials as the 

 dams, and are of various sizes according to the 

 number of individuals living in them. They are 

 conical, and may be eight feet high by forty feet 

 in circumference. Inside, and just above the 

 water level, is a large chamber which is con- 

 nected with the outside by a tunnel opening under 

 water. The chamber walls are about one foot 

 thick and, when frozen solid, defy the attack: 

 of the Beaver's fiercest enemy, be it Bear or 

 ^^'olverine. 



\\'hen the home is a burrow, the opening is 

 under water and a tunnel extends diagonally for 

 several feet, sometimes thirty, into the bank, 

 and ends in a chamber three or more feet in dia- 

 meter and about one foot high. 



In sunmner Beavers travel away from home to 

 a considerable distance, visiting other colonies 

 and exploring other streams, and the houses are 



