The chief resident of the caves for centuries has been the Mexican Free-tailed Bat (_Tadarida mexicana_), also sometimes called the guano bat because its species is especially noted for the huge quantities of commercially excellent guano it produces. The Free-tailed Bat is distinguishable from the northern bats by its extended tail which reaches about an inch beyond the interleg membrane, by its short fur, and by a strong odor not found with other species. They also possess short, stubby ears, will weigh between 10 and 12 grams, and prefer caves more than most any other species. The life of the bat is somewhat of a mystery to the average person, partly because they seclude themselves during the day in places relatively safe from discovery, and venture out at night when humans are not around and couldn't very well see them if they were. Bats resemble the ordinary field mouse in appearance, except for their large, expansive wings. They are mostly insectivorous, living almost exclusively on insects they catch while in flight, chewing their prey into the finest bits with their sharp teeth. A bat will eat enormous quantities of food between sunset and sunrise, and on the basis of only two full meals a night will consume an amount almost half its own weight. Their diet consists of beetles, flies, and other flying insects, most of which are enemies of civilization; thus the bat is economically a valuable animal. They leave the mouth of the cave at dusk, heading first for a drink of water at the nearest available spot, then spend the night in search of their food. As the sun's rays begin to appear in the east they fly back to the cave where they dig their tiny claws into the ceiling and remain there sleeping until the sun sets in the west and the cycle starts all over again. Due to their habits they have few enemies, the great horned owl being one. Very wide awake at night, he often catches an unsuspecting bat, chews the flesh, letting the bones drop to the ground where they remain as evidence of the owl's dinner. The mating season is normally in March. Along about June the young are born, with this species only one to a female, although in some species a litter of four is born. The single baby will weigh a fourth as much as its mother. Upon birth it clings to its mother's body night and day until it is strong enough to fly by itself, remaining tight even while the mother flies into the night in search of food. [Illustration: © BY ROBERT NYMEYER The famous bat flight--a nightly occurrence at the Caverns.] The habits of bats vary in respect to their living quarters. When insects are abundant, the size of the bat population increases, having been estimated at times to be as high as 7 million in the Carlsbad Caverns alone. As the supply of insects decreases, so does the number of bats. Where they go, and whether or not the same specific bats return in times of insect plenty is not definitely known.