Volume 3 - No. 3
MILLIONS OF BATS
By Harold J. Brodrick,
Bats, mysterious little creatures of the darkness, have been associated through the ages, in art and story, with Satan and the infernal regions, and as emblems of evil and darkness. It is little wonder that they are still the basis of several erroneous superstitions. The mere mention of the name still makes some people shudder. These flying mammals are of a very old and highly specialized group. They were hanging upside down in caves long before the cave man came to join them, and they have special senses of which man still has little knowledge.
Bats are clothed in fur instead of feathers. Their arms and fingers are greatly elongated to sustain a thin leathery membrane used as a wing. The thumb is free, and is armed with a strong claw, enabling the bat to climb walls and to run upon a rough surface. In this case the wings are folded and are used rather awkwardly as front legs. The hind legs and tail are connected with this some membrane. The bat suspends itself when at rest, with its hind foot, and hangs head down.
Their eyes are small, the vision is apparently short in range, but a bat can see in daylight as well as in darkness. The old saying, "blind as a bat", probably arose from the fact that they habitually fly in dusk or darkness. I have frequently had a captive bat follow me with his eyes, as I moved about him, or moved my hand toward him. The bats depend upon a mysterious sense that enables them to avoid objects, and to capture food, without the need of sight. Recent experiments indicate that they utter high-pitched staccato squeeks - too high a frequency for the human ear to hear - and by the rebound of these sounds they are able to avoid, while in swift flight, objects which they are not able to see. The bat's many sharp-pointed teeth enable it to capture and crush insect food, which it must catch while on the wing. Bats drink by swooping low over the surface of a pond or stream, scooping up a mouthful of water at each dip, until satisfied.
Approximately 230 species of bats have been classified as inhabiting North America. All of them are insectivorous. The fruit-eating bats and fabled vampires are tropical forms. The bats feed on, and help control, the night flying insects, just as birds do the daylight species. They feed rapidly and consume great numbers of insects. It has been estimated that if they were able to secure a full meal they would consume half their weight of insects every 24 hours. So far as we know the insects which are eaten are mainly injurious, so the economic advantage of a colony of bats is readily apparent. It has been estimated that the bat colony in an isolated cave in Carlsbad Caverns National Park, New Mexico, would consume several tons of insects in a night, based on the largest estimates for size of colony and the assumption that they all secured a full meal on the night's foray.
"Oh Ranger, am I too close?" "Will the bats get in my hair?" These are frequent questions from the feminine contingent of visitors as they are grouped around the entrance to Carlsbad Caverns, to watch the nightly bat flight. Well, there is nothing farther from a bat's habits or inclinations than to become entangled in a person's hair. No records are available here to show that this ever occurred. Bats will bite and fight viciously, if captured and held against their will, but if handled gently they are quiet and interesting little animals.
There are eighteen species of bats known in New Mexico. About twelve of these have been recognized in the vicinity of Carlsbad Caverns and the nearby canyons and caves. However, practically the entire colony that lives in the Carlsbad Caverns bat cave is the Mexican Free-tailed Bat (Tadarida mexicana). This is the famous guano producing bat of Mexico and southern United States. It roosts in enormous colonies, and gets its name from the fact that the tail projects nearly an inch beyond the attached membranes. They are rather small animals, with a wing spread of about 9-1/2 inches. They are dark brown in color, have short close fur, short wide ears, and a strong musky odor.
The free-tailed bat, like most other North American species, has only one young a year, born in May or June. The infant is carried about by the mother, clinging to the underside of her body, even while the parent is in flight. This continues until the baby is strong enough to shift for itself. Rather remarkable is the fact that the young bat weighs, at birth, approximately one-quarter the weight of its mother. The adult weighs one-half ounce, or slightly over. The same comparative weight in humans would mean a baby weighing about 30 to 35 pounds at birth. Mating apparently takes place in the early fall, before hibernation, but the embryo does not develop until spring.
Nearly every little cave in the vicinity of Carlsbad has its own colony of bats. Some of the smaller colonies are of different species than the free-tailed bat. However, the Carlsbad Caverns have the largest opening and the largest passages, thus providing a home for the largest colonies. This species is naturally gregarious and congregates in larger numbers than most other kinds. The immense deposits of guano that were found in the bat cave end of the caverns indicated that this cave had been in use for centuries. Guano has been removed over the period of years since 1900, and well over 100,000 tons is said to have been mined. It has been shipped chiefly to tho citrus regions of California. The market price originally was from $60 to $90 a ton. The price now is a great deal lower though this particular supply is nearly exhausted. That portion of Carlsbad Caverns has been in private ownership since 1900. The public does not have access to that particular cave, and the bats are not seen by visitors to the caverns, except during the evening flights. Originally this colony was estimated to number from 3,000,000 to 5,000,000 individuals, at the time the first studies of the caverns were made. The size of the colony varies considerably from time to time, and during the past few years it has been much smaller, with the best flights estimated te be in the hundreds of thousands, rather than in the millions.
The caverns were first thought to be the winter home from which the bats spread to surrounding territory for the summer. Recent observations and reports by owners of the bat cave indicate that most of the colony migrates southward while a comparatively small number hibernate over winter. During hibernation their respiration and other functions are reduced to the lowest stage that will support life. They appear at such time to be lifeless, as they hang singly or in clusters from the cave ceiling. The body tomperature becomes approximately that of the air. Occasionally after warm spells in the winter a few bats may stir around and appear in the caverns entrance in the evening, but they seldom fly far from the entrance.
The flights start in the late spring, gradually increase through June, reach their peak at intervals between late June and late August, then dwindle in the fall until they finally stop in late October. These flights fluctuate considerably throughout the summer. The controlling factor apparently is the available food supply, which in turn is governed by weather conditions. Observations over several years have shown that flights become smaller during continued hot, dry spells, and increase immediately after rainy periods. When their food supply is not adequate, due to adverse weather conditions, they fly off elsewhere for a short time.
The bats are strong and excellent fliers, and apparently range quite a distance on their nightly flights. Their first objective, as they fly from the caverns, is water, as they ordinarily fly in a long smoke-like column toward Black River, 6 miles from the caverns entrance. After satisfying their thirst they spread along the river valley and throughout the surrounding country. It is difficult to estimate how far they range, but the bulk of the colony probably feed over an area within a radius of 30 to 50 miles.
The nightly flights usually start from 30 to 40 minutes before dark, although frequently not until it is too dark to see them. These flights may be over in a few minutes or they may last for one or more hours, depending upon the season. Frequently the colony returns about daybreak, coming in from all directions and quite high above the entrance, where they circle a time or two, partially fold their wings, and glide through the entrance at considerable speed. The velocity of their descent creates a vibration in their wings which, in a large inbound flight, sounds much like the murmur of a distant waterfall. This sound is frequently sufficient to waken the occupants of the government residential area nearby.
Bats fortunately have very few enemies. Their habit of flying at night, and spending the days in caves, crevices or old buildings, puts them out of reach of most predacious animals or birds. Horned owls have been seen swooping out into the bat column as it pours out of the caverns entrance. On some occasions they have been successful in capturing a bat. Occasionally the Ringtail or Cave Cat might be able to reach an accessible bat that is hanging too near a ledge. Wind has been known to cause bats to strike obstructions that ordinarily they are able to avoid. The bats may have an average life of about 10 years. Very few dead are found under areas where the bats usually roost. However, in remote passages and in half hidden corners considerable deposits of bat bones, skeletons and mummies have been found. Apparently, like the fabled elephants' graveyards, the older bats, weakening with age, or others that may feel death approaching, seek these remote passages in which to die.
Inscription Rock, in El Morro National Monument, New Mexico, is the nation's largest autograph album. It is a one-page "book", over 200 feet high. No one has read the full page. Some of the signatures, symbols, and messages are so old that modern man has not been able to decipher them. Code experts have puzzled over them - and are still puzzled. Don Juan de Onate, founder of New Mexico, wrote a message in Spanish on Inscription Rock in 1604, two years before Jamestown, Virginia, was founded. Indian petroglyphs were placed there earlier. The last Spanish inscription is dated 1774, two years before the signing of the Declaration of Independence. The book has been closed to further writing, under a federal law which also provides penalties for persons who damage existing inscriptions.
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