But the canal is one of this animal's most interesting undertakings. It is strictly a freight canal for bringing in food-logs, and is dug out across level ground toward the standing timber.
Canals are commonly three or four hundred feet long, about three feet wide and two feet deep. There was a small but good example at Yancey's in 1897; it was only seventy feet long. The longest I ever saw was in the Adirondacks, N. Y.; it was six hundred and fifty-four feet in length following the curves, two or three feet wide and about two feet deep.
Three other Beaver structures should be noticed. One, the dock or plunge hole, which is a deep place by a sharply raised bank, both made with careful manual labour. Next, the sunning place, generally an ant-hill on which the Beaver lies to enjoy a sun-bath, while the ants pick the creepers out of his fur. Third, the mud-pie. This is a little patty of mud mixed with a squeeze of the castor or body-scent glands. It answers the purpose of a register, letting all who call know that so and so has recently been here.
The chief food of the Beaver, at least its favourite food, is aspen, also called quaking asp or poplar; where there are no poplars there are no Beavers.
THE DAM
Usually the Beavers start a dam on some stream, right opposite a good grove of poplars. When these are all cut down and the bark used for food, the Beaver makes a second dam on the same stream, always with a view to having deep water for safety, close by poplars for food. In this way I found the Beavers at Yancey's in 1897 had constructed thirteen dams in succession. But when I examined the ground again in 1912, the dams were broken, the ponds all dry. Why? The answer is very simple. The Beavers had used up all the food. Instead of the little aspen groves there were now nothing but stumps, and the Beavers had moved elsewhere.
Beaver using his Tail as a Trowel