National Geographic : 1918 May
THE NATIONAL GEOGRAPHIC MAGAZINE many mice are known to have continuous series of notes which are as evidently songs as the utterances of birds. Some of these notes, as in the case of singing mice, have a remarkably musical char acter, similar to the warblings of cana ries. Various unrelated species of mice have been observed singing, and a closer study of the life habits of these small animals may develop the fact that all are songsters to some degree. House rats and mice have, undoubtedly, been parasitic about the haunts of man from early times. From Asia they have accompanied him through his advance in civilization. With the growth of com merce they have traveled around the world, becoming transplanted to all lands and thriving in all climates. In various parts of America they have not only be come pests about human habitations, but where climatic conditions were favorable have reverted to the wild state and are competing with the native species in the fields. Of all the small mammals none have become modified to such an extent as the bats. As a group these mammals are of world-wide distribution except in the in hospitable polar regions. They are true mammals and present an extraordinary variation in size, from tiny little crea tures, almost as small and fragile as butterflies, to the huge fruit-bats, with a spread of wings like that of a wild goose. BATS WITH BULLDOG FACES The heads of bats are strangely sculp tured, some being smoothly contoured and shaped like those of little foxes; others appear like miniature bulldogs; and still others have curious cartilaginous nose-leaves upright on the muzzle. Some have the entire face molded into a hide ous mask repulsive to look upon. Their habits are equally varied to meet special conditions: Some are eaters of fruit alone; others feed solely upon in sects, while others bite other mammals, including man, for the purpose of drink ing the oozing blood, upon which they subsist. All are nocturnal, but some ap pear late in the afternoon, before the sun sets; most species, however, wait until the shades of night have covered the earth. Throughout the world the majority of the species of bats feed upon insects, but there are many fruit-eaters. The teem ing insects and plant life of the tropics afford a never-failing food supply, and the center of abundance of these animals is found there. In some localities be tween twenty and thirty kinds of bats exist, with such vast numbers of indi viduals that the bat population far out numbers all other kinds of mammals com bined. ANIMALS THAT PUT THEMSELVES IN COLD STORAGE In the northern parts of the Old and New Worlds many mammals, including bears, marmots, prairie-dogs, ground squirrels, and jumping mice, pass a large part of the winter months in a lethargic sleep called hibernation. While hibernat ing these animals have extremely slow and slight heart action and their bodily temperature falls far below the normal of their active periods. During the most profound hibernation an animal may be awakened if brought into a warm tem perature, but when again put into the cold at once returns to sleep. Preparatory to this sleep, during the summer and in the autumn, the hibernat ing mammals become exceedingly fat. It has long been generally accepted that the fat thus accumulated was for the purpose of being gradually absorbed to nourish the animals during their long fast. As a matter of fact, during this period the bodily functions appear to be practically suspended and the animals may be said to be in cold storage. This is evident from the fact that observations have been made of ground-squirrels, and even bears, emerging in spring, after their long winter sleep, practically as fat as when they retired in fall. Hibernat ing animals become extremely active as soon as they come out in spring and quickly lose the fat which should be of special service to them, owing to the tem porary shortage of food they experience at this season. Most hibernating species do not retire for the winter until cold weather is at hand, in September or October, at times remaining out until after the first snow has fallen. The animals which retire 382'