IT FLIES BY EAR
A. C. ANDERSON
Lay that shotgun down ! They may be ugly, but bats are really okay at heart, and smart, too
Hat, bat, come under my hat,
And I'll give you a side of bacon.
THIS OLD nursery rhyme was written when some people thought bats flew down chimneys in search of bacon hung in the fireplace to smoke. And then someone actually tried feeding bacon to captured bats. They learned bats would rather starve to death than eat it.
The bacon myth representa the sort of misconception that has always surrounded the bat. Few animals are so widely misunderstood. They are thought to be part bird, part mouse, to be blind, to nest in women’s hair, to eat snakes, steal babies, and any other nonsense we like to imagine. This harmless creature, the size of a sparrow, can make women hysterical and men shudder.
The bat is not a bird. It is not a mouse. It is not a lizard with wings. The bat is a mammal, just as you are a mammal. And like you he also has a nose, two ears, and a mouth with a set of teeth. Females bear young one at a time and suckle them at a nipple. Their wings have no feathers but consist of skin stretched between modified and
greatly elongated fingers of their front limbs. And when we say “blind as a bat,” the bat might well retort “stupid as a man.” Being a night-flier he seldom uses his eyes, but they are perfectly developed and he can see well enough when he needs to.
Approximately one thousand bat species have been classified and authorities think that twice this number will be listed when the job of recording is filially finished. In the tropics they are found in large numbers and large sizes, some with a wing spread of four feet. They are numerous enough to outnumber any other mammal in the hot countries, but they are not plentiful in Canada. And our few species are quite small, being the size of a mouse with a wing span of eight to 10 inches.
In spite of their relative scarcity, many Canadians, even city dwellers, occasionally find bats in the house. Immediately they worry about destroying them before they spread disease or peck out the baby’s eyes. Actually from Halifax to Vancouver you will not find a single bat that does eit her.
They merely sleep all day and fly at night in search of insects. No bloodsucking; no eating of snakes or stealing of babies; no spreading disease and no yearning for women’s hair. Nothing but sleep and insects. Sorry.
If they adopt your house the accumulated droppings may become objectionable, but there is no need to storm the attic with a rifle or a club. The United States Fish and Wild Life Service recommends naphthalene flakes spread where they roost. It is a gentler discouragement than violent death and causes the useful bat no harm. It simply puts
him to the inconvenience of moving into someone else’s house.
Most of the commonly encountered bats in North America belong to the family Vespertilionidae, and Canada does not have any unusual types. Cold countries never harbor many varieties and if you capture a bat it will probably belong to this family and be of the genus Myotis, some of whose species are found as far north as the tree limit from Labrador to Alaska. The common little brown bat, Myotis lucifugus, is one of this group.
If you have watched a bat in confined quarters, perhaps trapped in a room, you have been amazed by its dexterity in flight. It excels most birds in the irregular, jerky sort of flying it does best. As it dips and banks and dives and darts to and fro, brushing obstacles with its wing tips but never flying into anything, it seems to have perfect flight control. And what is even more interesting the bats fly in pitch darkness with the same unerring accuracy. You might conclude that, their eyes respond to light waves we cannot see, but that theory was eliminated a century and a half ago when investigators showed that blinding a bat did not lessen its ability to dodge. The same early experimenters discovered that deafening a bat caused it to blunder into things a normal bat would miss. These observat ions suggested that bats use ears, rather than eyes, to guide them in flight, but it was not until recently that the 150-year-old riddle was solved.
The facts were exposed by Dr. Robert Galambos and Dr. Donald Griffin of the Harvard University Biological Laboratories. Continued on page 71
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It Flies By Ear
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In a soundproof room they released captive bats and noted how easily they avoided small-diameter wires hung from ceiling to floor. Some of the bats were t hen temporarily deprived of sight by coating their eyes with dark blue collodion. If anything, the blind bats flew between the wires with increased confidence. The scientists then dissolved off the collodion and restored the animals’ sight. They then plugged the ears with drops of collodion that hardened to produce an artificial deafness. The moment the deaf bats were released they floundered about and flew against wires they had previously missed with ease.
The experimenters now removed the ear plugs but bound the snouts of their captives with thread. Thus rendered mute the bats blundered into wires just as they had with their ears plugged but their mouths free. Interesting indeed, said the scientific men; plug the ears or close the mouths and the bats fly as if they were drunk. Obviously their control depends on the simultaneous use of mouth as well as ears.
As early as 1920 it had been suggested that bats utter a shrill cry and were guided in flight by the echo of the sound from nearby objects. That theory was certainly not at variance with the observations of Galambos and Griffin, except that if the bats did emit such a cry it was not audible to human ears. In the experimental room the little animals had banked and swerved, flitted and dodged, avoiding walls and wires with consummate ease—but all in silence save for an occasional squeak.
The Harvard men decided on more rigorous tests. They suspended their work long enough to borrow electronic
sound apparatus. They knew the sounds human ears can pick up are confined to a narrow range of approximately 20 to 16,000 vibrations per second. The lowest note of a piano is 27, the highest about 8,200. Above the audible range lies what is termed the supersonic range of frequencies, and the experimenters wanted apparatus that would intercept supersonic sounds and convert them to lower frequencies that could be heard through a radio speaker. Soon they were again ready for the bats.
Sees With Ilis Ears
The supersonic amplifier came to life with a chattering of bat sounds inaudible to the unaided human ear. They discovered each bat was giving, in a quick succession of cries, somewhere near 50,000 vibrations a second —well beyond the limit of human perception.
To most people this would be conclu sive proof of how hats fly faultlessly in the dark. But science demands irrefutable evidence and the two men cautiously resorted to physiological experi ments to determiné whether a bat’s ear can actually catch the high-frequency calls issuing from its mouth. They found it could, although for no other mammal had a frequency response been detected beyond 35,000 vibrations a second.
And so our little friend is unique in more ways than his webbed fingers and our traditional misunderstanding of him. His hearing is acute almost beyond comprehension, and his reactions so fast he changes direction a split second after his ears give warning.
The next time a bat flutters about your head in the dim light of the woodshed, remember that he can “see” you perfectly with his ears. He is eminently
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capable of avoiding a collision and unless your hair is full of large insects he has no interest in it. But you will probably forget this entirely. You will picture him tangled in your hair or sucking your blood, and if you are a normal female you will shriek in terror for your husband. That brave man will rush in with a shotgun or an axe and fight the bat monster to the death — though if he’s smart he’ll arm himself with a broom or a badminton racket. You can see what we mean about the bat being misunderstood.
A number of years before Galambos and Griffin proved that bats use a sound - echo system, humans had rivalled nature by applying the same principle in almost the same manner. One of these applications gave us an altitude meter for aircraft. A radio signal transmitted from the plane is reflected by the earth, the time interval being a measure of the craft’s altitude. The control and accuracy are admittedly not as great as the bat achieves, but that clever Homo sapiens is certainly catching up to his fellow mammal.
Even radar, that boy wonder of the electronic family, is nothing more than reception of a reflected radio wave coming back from some object in its path. A patent attorney would hesitate to allow man a prior claim to novelty on that one. Of course the radar engineers have developed their instrument to a remarkable degree of sensitivity, and at one time it was the most important secret weapon in the Allied Gommand’s bag of tricks. But its essential principle is the same as the bat’s. It is humbling to reflect that our best scientific minds, groping to extend the power of man’s own five senses, should at last have developed a system identical to that which bats have used for a million years.
If you are not a movie fan you may have forgotten the vampire is a ghost that stays in tiptop shape by drinking blood. It masquerades in human form, keeps its clothes neatly pressed, and is able to woo innocent maidens and work all manner of mischief. This bloodlusty “undead” chooses sleeping victims and does its job so neatly that the subsequent death is often blamed on anaemia of unknown origin. The vampire tradition is prominent in folklore and even today is a force among primitive races and superstitious
peoples. The accepted ways of assuring their destruction are: burning, driving a wooden stake through the heart, shooting with a silver bullet, or striking oft' the head with a sexton’s shovel.
A family of tropical bats, the Desmodontidae, has been tagged with the sinister name “vampire” simply because Nature fashioned them to live on blood just as she did the mosquito and the louse. They are innocent of any desire to inspire terror and subsist on blood because that is their natural food. Animals and birds are their usual prey but they are not impartial to human blood if they find an accommodating donor. An exposed nose or foot is acceptable.
This tropical bat’s method of getting blood is not as terrifying as Dracula’s. It is true their teeth are sharp and long, admirably functional, but they merely inflict a shallow wound and lap the blood that oozes out. They are night lovers, as all bats are, and their incision is so slight that the victim often slumbers on without wakening. It is interesting to note that a short shallow wound clots over slowly and bleeds longer than a deep bite. The vampire bat instinctively recognizes this when it uses its teeth. It is not a large animal and a single repast is nota serious bloodletting for either humans or cattle.
However there is no doubt about the insect-eating bat being a friend of man. If he were a pest it would be serious, because the bat has few natural enemies and when the climate is suitable they increase to the limit any region can supply food. Their natural hazards of existence are so few that they multiply prodigiously, though producing only one offspring a year. Most North American species sleep away the day in caves or empty buildings and are thus safe from predatory life that might consider bat meat a tasty meal. When they are awake the excellence of their night-flying keeps them out of reach of potential enemies that share the darkness with them. Owls catch a few, but generally the bat realizes his eight or 10 years.
In regions where food, climate and sleeping facilities are satisfactory the bat colonies grow to enormous size. In 1937 at the Carlsbad Cavern in New Mexico one observer gauged the evening flight of bats to exceed eight millions in number. In these extensive caves the bats have roosted for thou-
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sands of years. The guano deposits
from their droppings have been worked commercially as fertilizer and it is estimated that more than 100,000 tons were dug from the Carlsbad Cavern. In some places it was 100 feet deep.
Insect food in our country comes to an end as winter approaches and the bats have to migrate south or else hibernate during the cold months. Migrators, such as the hoary bat Lasiurus cinereus, fly to the southern States. Others remain and seek a shelter which they know from experience will stay above freezing. Almost all the bat species in Canada are hibernators. In limestone caves of central Vermont, across the border southeast from Montreal, temperatures were recorded while bats were using them as winter quarters. It was discovered that the knowing animals had selected a cavern where the temperature was above freezing even when the outside weather was 20 below zero.
The body temperature of human beings is remarkably constant. A shipwrecked sailor may cling to a raft in water almost freezing, but his blood temperature is maintained until he collapses. Cellular chemical reactions generate increased heat for the emergency. If they cannot produce heat fast enough or long enough to outride the emergency, he dies. The hibernating species of bats do not have this ability to regulate body warmth. Their normal temperature in summer is a few degrees higher than the human’s but if the surrounding air chills appreciably, then the bat does too. In winter the blood of a hibernating bat may be only a degree or two above freezing.
The hibernating condition is a deep, lethargic sleep during which the animals are easily approached. If one is lifted down from its resting place it will slowly be roused, but before it is awake a thermometer can be inserted in its mouth. With the great reduction in blood temperature their body processes become torpid. In fact they almost stop. The limbs grow stiff with cold while the respiration and heart
beat are so faint that the hibernating animal is easily mistaken for a dead one. Their metabolism, which is the medical term for the rate of consuming body fats, is so reduced that they sleep through the winter without food. It can be disastrous if a spell of warm weather brings them temporarily out of the hibernating sleep. Their body activity immediately increases and they start to burn up the precious store of fat accumulated in summer. Under such conditions they might starve to death before the spring insects appear. Even under normal conditions a bat loses a third of its weight in winter.
For warmth the bats hibernate in close-packed clusters, their bodies huddled together to retain the heat. The same caves are sought out year after year and many square feet of the roof space may be covered by a solid mass of them. If, by mischance, they are exposed to temperatures below freezing, ice crystals form in the lungs and they quickly die.
While hibernating the bat hangs head down, the tiny claws of its hind feet hooked securely over some projection in the surface of the roof. When asleep during the summer daylight hours it assumes the same position. Its wings are folded close and the head tucked in so nothing is visible but a small bundle of fur with projecting ear tips and perhaps the outline of a folded wing. There is nothing sinister about a furry mass hanging head down, but its appearance is outside the common range of human experience. When children notice a bat hanging from the rafters they become vaguely apprehensive. They run for Daddy, who in turn runs for a shovel or a stick of cordwood. The sight of the sleeping bat is no more reassuring to Daddy than it is to the rest of the family. He is just as uneasy as they are so he plays it safe with a resounding whack of the shovel. The harmless bat dies and the safety of the home is assured.
Bats have often been kept in captivity, but as one authority notes, they never look upon their captors as more than a convenient source of food. They do not really tame and they frequently die in a short period. But they quickly become accustomed to human presence
and readily accept insects or lap up water that is offered. If frightened they will use their tiny teeth, but usually they cannot puncture the hard skin of a finger. Their habits are cleanly and although they carry bugs, just as other animals do, it is agreed that none of the bat parasites will exchange their host for anything man has to offer. Our species do not spread disease and they are only objectionable because the droppings have a strong odor.
Like the ants, fish, and other life that has survived millions of years, the bat has adapted itself to many kinds of environment in different parts of the world. In North America they are insect eaters but in other countries they prefer fruit—and of course there is the notorious vampire. For us the bat is an economic asset because of its insect diet. It was once considered they might be a factor in the control of malariaspreading mosquitoes, but later investigation showed that mosquitoes are not a particularly favorite food of the bat.
The bat violates three principles that might make it easier for him to win friends among people. What he really needs is a public-relations adviser.
In the first, place he sleeps when we are awake and seeks his food by night. We rarely observe him at close quarters so he never achieves the intimacy of the sparrow or the robin. Ignorance breeds misunderstanding and what we cannot see our imagination pictures for us, often in a grotesque and terrifying form. We attach to his night habits a sinister interpretation and associate him with phantoms, murderers, and other night prowlers.
Causes Panic on Train
One summer day, a few years ago, I was a passenger on the afternoon train from Montreal to Ottawa. We had barely pulled out of the station when a small bat began to fly in a frightened manner up and down the length of the coach. Presumably it had flown in to most in the early hours of the morning while the empty carriage was on a siding. A 40-foot, python could not have created more confusion. Women screamed hysterically and held magazines over their heads to keep it out. of their hair. A small girl clung to her mother and the two of them shrieked in terror. Every physically fit man in the coach beat the air bravely with a newspaper.
The bat’s dexterity in evading its murderers was amazing, but in the end it was knocked to the floor and crushed under a male foot. Now a small bird would have been the same size. A small bird would have flown in bewildered fashion up and down the aisle just as the bat did. But had it been a bird someone would have opened the end door and let it escape, while the womenfolk looked on approvingly. People are used to seeing birds but they are not accustomed to bats, except in bloodcurdling movies with Dracula and other monsters. It was an interesting example of mass hysteria rooted in ignorance.
The second unhappy characteristic of the bat is that whenever we do get a close look at him, usually when a neighbor has killed him with a stick, his gnomelike face Ls shockingly ugly.
Finally, in addition to seeking the dark and having a face that’s far from pretty, he has skin stretched between his fingers. He could not fly without it., but unfortunately we are just not accustomed to long, clawlike fingers with webbed skin. We tolerate such things in Boris Karloff but we pay to see him and the psychology is different. When we encounter the real thing we are shocked.
It. is the bat’s misfortune that man is only human after all. ★