Photo by Dr. R. W. Shufeldt] [Washington.
MUSK-RAT.
A small water rodent, a native of the North American rivers. Immense numbers are killed for the sake of their fur.
The beavers' engineering feats have for their object to keep up a uniform depth of water in the streams where they live. On large rivers there is always enough water for the beaver to swim in safety from its enemies, and to cover the mouth of the hole which it makes in the bank, just as a water-rat does. But on small streams, especially in Canada, where during the winter the frost prevents the springs from running, there is always the danger that the water may fall so low that the beavers would be left in shallow water, a prey to the wolverine, wolf, lynx, or human enemies. To keep up the water, the beavers make a dyke or dam across the stream. This they go on building up and strengthening until they have ponded back a large pool. In time, as they never seem to stop adding to their dam, the pool floods the ground on either side of the stream and makes a small lake. It flows over the parts of the bank where their holes are; these also become filled up, because the beavers carry into them every day fresh quantities of wood-chips to make their beds. The beavers then scrape out the earth on the top, pile sticks over this, plaster the sticks with mud, and so build a dome over their bedroom. In time this is raised higher and higher, the artificial lake rises too, and the complete "beaver-lodge" surrounded with water is seen. The old trappers who found these in situ imagined they were built at once and outright in the water. The experiments and observations at Leonardslee, in Sussex, where Sir E. G. Loder has kept beavers in a stream for ten years, show that the "evolution" of the lodge is gradual and only incidental. But the building of the dyke, the cutting of the trees, and the making of the pool are done with a purpose and definite aim.
Photo by W. P. Dando] [Regent's Park.
GAMBIAN POUCHED RAT.
These rats are able to carry food in their cheek-pouches, which are used as pockets.
What this is, and how done, is explained in the following description of the beaver colony at Leonardslee: "Their first object was to form in the brook a pool, with water maintained at a constant height, to keep the mouth of their burrow in the bank submerged during the droughts of summer. To this end they built a dam, as good a specimen of their work as can be seen even in Canada. Its situation was carefully chosen. A small oak, growing on what appears to have been a projection in the bank, gives support to the work. It may be concluded that this was part of their intention; for though they have cut down every other tree in their enclosure to which they had access, except two or three very large ones, they have left this small tree which supports the dam untouched. (Later, when the dyke was stronger, they cut it down.) Above this stretches the dam, some 12 yards wide, and rising 5½ feet from the base to the crest. The beavers built it solidly of battens of alder, willow, larch, and other straight-limbed trees, cut into lengths of from 2 to 3 feet. The bark of each was carefully gnawed off for food; and the whole work, constructed of these cut and peeled logs, has a very regular and artificial appearance. Smaller twigs and sticks are jammed in between the battens, and the interstices are stuffed with mud, which the beavers bring up from the bottom of the pool in their mouths, and push in with their feet, making the whole structure as watertight as a wall." This dam converted what was a narrow brook into a long lake, some 50 yards by 15 or 20 yards broad. Later the beavers made another larger dam below this, cutting down some more trees. One tree gave them a great deal of trouble; it was a beech, 40 feet high, and hard to gnaw; so they waited till the water rose round it, and then dug it up. When the large dam was made, quite a considerable lake was formed below the first. They then neglected their first dam, and let the water run out of the top lake into the lower one. At the time of writing there are five old beavers and a family of young ones at Leonardslee. The work done by these beavers, so few in numbers, shows how large colonies may alter the course of rivers.
The Dormice.