OCR Text |
Show BATS OP THE CARLSBAD CAVERN 323 arranged on the sides of the breast, just above the cradle of her warm, fur-lined armpits. During the mother's flight the young, even when half grown, cling to her body and are carried about in her nightly search for flying insects. T h e y fly considerably b e f o r e becoming full grown, and apparently develop very r a p i d ly from birth to the time of their first flight. The mating season of most of our bats is in late summer or autumn, but the embryos usually show little development u n t i l the following spring. Soon after the bats in t h e Carlsbad Cavern awoke from hibernation the embryos were still minute and in some individuals could scarcely be detected. In others they were perfectly formed, with a well-developed vascular system. By April 24 they were as large as small buckshot, and by May 7 the size of a .44- caliber bullet. They steadily increased in size until June 13, when they were fully developed, as large as marbles, and ready for birth. One examined on this date weighed 3.6 grams, while the mother weighed 13.6 grams. The birth of these young, fully a quarter as large as the mother, would not be possible except for the low and widely separated bones of her pelvis. Even then it is almost inconceivable that she could give birth to a young comparable to a 33-pound, two-year-old child of the human mother. THE BATS HANG IN VAST COLONIES FROM CEILINGS OF CAVERN With but one young a year, it would seem that bats must live long to keep up their normal abundance, but there appear to be no available data as to their longevity or as to what becomes of them when their life cycle is closed. Generally they have Photograph by Vernon Bailey THE FACE OF AN ANGRY BAT Caught and held in front of the camera against their will, these mammals express their rage with fierce looks and squeaks and use their keen little teeth on anything within reach. few enemies, and their abundance is probably limited only by the normal food supply. The bats of the Carlsbad Cavern are mainly the Mexican Free-tailed, Tadarida mexicana, the famous guano-producing species of Mexico and the southern United States. Their habits of roosting in enormous colonies in caves or buildings has given them a special value in the production of great quantities of guano, a product much prized as a fertilizer. They differ from most of our northern bats in the projecting tail, which reaches about an inch beyond the attached membrane ; in short, wide ears, short, close fur, and a strong, musky odor peculiar to the species. They are not the only species of bat in the great cavern, but are so numerous that the others are little noticed (see illustrations, pages 325 and 327). Their numbers vary at different seasons, apparently reaching the maximum in late summer and early fall, when they gather for the winter's sleep, and the minimum about the first of May, when |