The African apes have an interesting way of sending their sentinel to the top of an adjacent rock or tree, that he may look over the surrounding valleys and plantations before they go to plunder a garden or field. If he sees any danger, he utters a loud shriek, and the entire troop immediately runs away. The monkeys of Brazil post a guard while they sleep; the same is true of the chamois and other species of wild antelope.
A few years ago, many of the sheep in the northern part of Wales had become quite wild, and they usually grazed in parties of twelve to twenty, always having a sentinel so stationed as to command a prominent view of the surrounding territory. If any animal or person came near, he would give a peculiar hiss or whistle, repeating it two or three times, at which the whole herd would scamper away to places of safety.
One of the most striking facts about migration is its never-failing regularity and success. Most animals migrate at the recurrence of the breeding season. Of these, the great sea-turtle, which seeks the shallow water and deep sandy hills when ready to lay her eggs, is well known. Notwithstanding the great risks that practically all travelling animals assume, they are successful as a whole in their travels, and many return to bear testimony to a successful trip even across continents and sometimes the ocean. They migrate, for a variety of reasons. When it is not for a more desirable climate, nor more food, nor even better breeding grounds, we must either believe it is because of the natural desire to travel, or frankly admit that we do not understand it.
The Icelandic mice have probably the most curious methods of travelling of all migratory animals. Dr. Henderson, an authority on Iceland, not only verifies the fact himself, but gives the names of many prominent investigators who have seen the mice crossing small rivers and streams on thin pieces of dry board, dragging them to the water, launching them, and then going aboard their little rafts. They then turn their heads to the centre, and their tails, which hang in the water, are used as paddles and rudders until they reach the destined shore.
Among travellers none are more famed than the camels. In their sphere and use they are supreme, and Nature has prepared them especially for travelling on the dry, hot, and barren deserts. They are truly the "ships of the desert" for they travel on a sea of sand, and their pad-like feet, so poorly adapted for travel on moist soil, is admirably suited to the desert sands. They are capable of travelling many days without food or water, and are used extensively in the desert regions of the East not only as beasts of burden but for their milk, which is an important article of diet in those countries where the camel is at home.
Animals that do not migrate, especially those living in cold climates, change their clothing at regular intervals. Their hair or fur increases in thickness in winter. If we compare the Indian and African elephants of to-day, whose delicate thin hair is scarcely noticeable, with the great extinct mammoth, which had an enormous amount of woolly fur, we readily see the great difference in their clothing. Yet these animals are members of the same great family. The same difference may be noted with horses: the Arabian horse, for example, has short, glistening fur, while those of Iceland and Norway have very thick fur; the same is true of Northern and Southern sheep. Animals which live in temperate regions, put on much thicker coats in winter, and shed them as summer approaches.
American Museum of Natural History, New York
THE BLACK BEAR IS NOT ONE OF THE GREAT MIGRATING ANIMALS. THE THICKNESS OF HIS COAT MUST THEREFORE CHANGE WITH THE SEASONS.