THE TRUCKEE-CARSON DAM THREATENED
In Nevada, as in Holland, mice must be exterminated, if possible, or at least have their operations most carefuly guarded against, if the safety of some very costly and important hydraulic works is to be assured. Of the works thus menaced in the big Truckee-Carson diversion dam, whose usefulness in settling a desert region with farmers may be neutralised by these destructive little animals unless the United States Biological Survey can find out some means of exterminating them. This dam is part of the Truckee-Carson irrigation system undertaken by the Federal government and now in course of development only a few miles southwest of the Humboldt valley. These field mice have already devastated the alfalfa crop, and, if they begin burrowing (as they will) in the banks of the dam, they will cause a most destructive break. These meadow mice are among the most prolific of mammals. In the Western States they range from Alaska to Lower California. The species that is under consideration is Microtus Montanus, a brownish-gray animal of 6 to 7 in. in length. They have runways on the ground and burrows underneath in which they live and rear their young, of which there are front four to six in a litter. Estimating the normal increase at four litters a season, and assuming there are no checks upon the increase, a single pair and their young in five seasons might amount to nearly 1,coo,coo mice. At all seasons of the year they feed on grasses, green vegeta tion, unripe seeds and fruits, and in Nevada, not content with gnawing down the alfalfa, have attacked the roots. Notwithstanding the owls, hawks and other birds, which, with skunks and coyotes, feed upon them, and the efforts of the Biological Survey to wipe them out by poison and inoculating them with an infectious disease, just a few miles above the Carson basin the mice arc devastating the land. In a year ot two the lands round the basin will be under irrigation, and the crops will be planted. Large capital will be invested in farming, and, if no steps are taken to destroy the mice of the Humboldt area, it will be only a short time before they will migrate to the hundreds of thousands of acres of the Carson basin, and, once in that section, it would Ire a huge task even to limit their depredations, let alone exterminate them.