The food of the beaver is the bark of aspen and willow trees. He does not eat fish or meat. Instead of hibernating in winter, beavers harvest a quantity of food-supplies in the autumn and store them for winter use. These are piled in the water beside their house. After gnawing down trees, cutting them into sections, and eventually eating the bark, they use the wood in constructing dams and houses. Besides taking thought for the morrow, they build permanent homes, and keep them clean and in repair. They skillfully construct dams and canals to insure a constant water-supply in which to live, work, play, and travel. These give a charm to landscapes, and are a benefit to mankind. Beavers were the world's first engineers and the first conservationists. They have industry, patience, and persistence, combined with mental power. They live in colonies or communities. Evidently they know the wisdom of the old saying "All work and no play," etc., for they often play as well as work, and also take a long summer vacation. Excellent workers as they are, they avoid unnecessary labor and do less of it than any other animal I know. There were civic centers in the animal world long before man conceived such an idea for himself. The mountain lion is one of the slyest and most elusive animals in the woods. Rarely is it seen, although its keen curiosity leads it to come close to camping-parties and to follow individuals through the woods. On the lower slopes of most Parks a few snakes are found, but they are wholly absent from the middle and the higher slopes. In most of the Park streams trout are found--Western brook trout, Eastern brook trout, and California rainbow trout. Among the more prominent birds common in a number of the Parks are eagles, grouse, ptarmigans, Clarke crows, camp-birds,--Rocky Mountain jays,--robins, bluebirds, blackbirds, song sparrows, white-crowned sparrows, cañon wrens, solitaires, and water-ouzels. In several of the National Parks a number of species of hummingbird are found. Each spring many species of birds migrate up the mountain-slopes, where they nest in the alpine heights. The mountain migration, requiring a flight of only an hour or two, gives them climatic conditions similar to that of the Arctic Circle, to reach which would cost them a journey of several thousand miles. Some species bring forth two broods each summer. The first is raised in the lowlands, where the young are fed while flower life in the lowlands is at its best. As soon as the young birds are able to care for themselves, the parent birds move up the mountain-side into the very heart of summer. Here they nest again. How romantic is every habit and custom in Bird World! The second nest of children is thus reared on the alpine slopes. This enables the old birds to bring up each brood in the midst of an abundant food-supply. The white-crowned sparrow and two or three species of hummingbird do this.