Owls Aren't Wise and Bats Aren't Blind (10 page)
Over the years, I’ve had many memorable and often amusing encounters with porcupines. However, what was certainly the most bizarre occurred within a year or two of our dog’s contretemps with the porcupette. It happened in this fashion.
I was driving past a dairy farm and, having grown up on such a farm, slowed down to gain a better view of a particularly nice-looking herd of Holsteins milling around a feed bunker. To my dismay, a porcupine suddenly appeared, waddling unconcernedly toward the cows, which were some distance away and still hadn’t noticed their novel visitor.
I had no usable weapon in my car, and, fearful of the result if cows and porcupine came together, I wheeled into the farm’s dooryard and knocked on the farmhouse door. The young farm wife appeared, and I hastily introduced myself and explained the impending disaster. She was quite properly suspicious of me at first, but I finally convinced her that I was, in fact, a forester employed by the state.
Unfortunately, her husband and the hired help had gone off on some errand. I inquired if there was a gun handy. She quickly found one, but didn’t know where her husband kept the ammunition. I then told her that, in a pinch, a stout club would do, and she finally located a baseball bat. Grabbing the bat, I ran for the pasture.
Alas, all of this had taken time—too much time. When I reached the pasture, it was evident at a glance that my worst fears had been realized. The cows were clustered around an extremely dead porcupine, trampled by the hooves of very large bovines, while the fleshy, bulbous noses of several of the Holsteins were stuck full of innumerable quills!
I returned the baseball bat to the wife and broke the bad news to her. I’ve often wondered since then whether the farmer endeavored to pull the quills himself or had to call a veterinarian to tranquilize the beasts before extracting the porky’s darts. Knowing the tremendous strength of an upset cow, I’d bet on the latter.
Porcupines are full of surprises. One of the most recent concerns their skill in tree climbing. Porkies have always been regarded as slow, awkward, but nonetheless very able climbers, since they spend much of their lives in trees. Lately, however, biologists have learned that it’s not uncommon for porcupines to fall out of trees and injure or even kill themselves!
Possibly some of the porky’s arboreal difficulties stem from its somewhat unusual method of locomotion. Whereas most mammals grip a tree with their front feet and propel themselves with their hind legs, porcupines do exactly the opposite. As it holds the tree with five strong, sharp claws on each hind foot, a porky reaches up, one front foot at a time, sinks the four front claws into the bark, and hauls itself upward in hand-over-hand fashion. Descent reverses this mode, as the porcupine climbs down tailfirst.
Now that the fisher has brought porcupine numbers down to a normal level, encounters with the clumsy rodents have become uncommon enough to be distinctly pleasurable under most circumstances. My most recent experience with a porky is a good example.
While deer hunting in a few inches of fresh snow, I spotted suspicious-looking tracks some distance away. I hastened to investigate, and even before reaching the tracks, my nose told me that it belonged to a porcupine. Porkies tend to have a rather pungent odor, much of which stems from living in a den carpeted with porcupine dung, and the slight breeze wafted the telltale scent to my nostrils from a distance of several feet.
The opportunity was irresistible, and I followed the broad trail, complete with tail-drag marks, for two or three hundred yards. There the trail ended at a hemlock of modest proportions. Gazing up into the tree, I searched and searched for the track maker, which, unless it had sprouted wings, was surely in the tree.
Finally, after looking futilely for some time, I happened to glance at a spot far down the tree, where I was startled to see the porky on a branch barely above my reach. This was a wonderful chance to observe a porcupine at close range, so I stood there and watched.
The porky seemed totally unfazed by my presence. It was nipping off the tips of hemlock twigs and masticating them in slow but purposeful fashion, and it seemed to have no intention of interrupting that useful activity. From time to time it paused for a few seconds to gaze incuriously at me with its dull shoe-button eyes—then resumed its munching.
For quite some time I stood there, talking softly to the porky, which of course paid not the slightest attention to my meaningless sounds. Finally, with considerable reluctance, I went on my way, leaving the porcupine to continue its contented feeding. The experience brightened my day greatly, though it’s doubtful that it made any great impression on the porky.
Although porcupines have often been regarded as intolerable nuisances, it hasn’t always been thus. For example, at one time—either by law or custom—it was considered bad form to kill a porcupine in areas of extensive, trackless forests. The theory behind this was that the porcupine was the only animal that a lost and unarmed person could easily kill for food in order to survive. In fact, a porcupine
is
easy to kill: a sharp blow on the end of the nose with a club or stout stick will dispatch one with ease. It’s unknown how many lost souls were actually saved from starvation in this fashion—probably very few—but the theory at least sounded good!
Native Americans had an even better opinion of the porcupine, and held it in high esteem. In some of their legends, the porcupine is something of a hero, and indeed, they found the porcupine to be a most useful creature. It was easy to kill, and its meat was deemed a delicacy, an opinion confirmed by a number of people in recent times. Further, its quills, often dyed, were widely used to make handsome decorative designs on such things as baskets and canoes, as well as a form of jewelry for personal adornment.
Our own perception of the porcupine is changing, too, especially now that porkies are no longer present in excessive numbers. True, a dog may occasionally run afoul of the quill-bearing rodent, or a porky may cause damage by gnawing on anything from a tree to a tool handle. Nonetheless, more and more we’re recognizing the plodding, seemingly imperturbable porcupine as an important component of the forest ecosystem; more significant, we’re perhaps beginning to fully appreciate the unique qualities of this mammalian curiosity.
Big brown bat
6
Evasion Beats Entanglement: Bats
MYTHS
Bats are blind.
Bats fly into people’s hair.
Bats pose a major threat of rabies to humans.
Bats are a sort of a flying mouse.
MONSTROUS BEYOND IMAGINING, ALL-CONSUMING, BLACKER THAN BLACKEST NIGHT, THE HIDEOUS SATAN IN THE
NIGHT ON BALD MOUNTAIN
SECTION OF WALT DISNEY’S
FANTASIA
SPREADS GIGANTIC BAT WINGS AS IT TURNS FIERY EYES TOWARD THE LOST SOULS ABOUT TO BE ENGULFED IN WRATH AND FLAMES. This batlike depiction should come as no surprise; it’s merely another manifestation of the fear, horror, and superstition with which bats have been regarded down through the ages.
In any drawing of a haunted house, bats are likely to be seen emanating from its towers and windows. Bats were also regarded as “familiars”—that is, spirit helpers in animal form—of witches. Evil witches in conical hats— toothless hags on airborne broomsticks—usually are shown with a flight of companion bats, like a swarm of night fighter planes shepherding a heavy bomber on its deadly journey. Indeed, one unfortunate woman in fourteenth-century France was burned as a witch for no better reason than the abundance of bats around her home!
Bats have also figured prominently in potions and curses. “Wool of bat” is a key ingredient in the witches’ brew in Shakespeare’s
Macbeth—
a concoction that surely rates as the most unappetizing cookery of all time! And in
The Tempest,
Caliban includes bats with such things as beetles and toads when invoking his curse on Prospero.
Even in this modern age of supposed enlightenment, millions of people still shudder at the vision of bats flying at their heads to entangle themselves in human hair, or of bats as fiendish vampires sucking the blood out of their victims. To all of these has been added the overblown fear of rabid bats.
All of this is truly sad, both for bats and humans. Because of superstition and irrational fears, bats are among the most persecuted of all our mammals. We humans, too, are impoverished by these archaic attitudes, for bats are unquestionably among the most astonishing and fascinating of all living things.
So complex and intriguing are bats that it’s difficult to know where to begin in telling their story. However, the origins of bats and the structure that gives them the ability to fly represent as good a starting point as any.
Approximately 55 million years ago, and nearly that long before we humans even existed, bats had evolved into winged creatures—the only mammal that truly flies. The earliest known fossils are from the early Eocene period. In geological terms, this is a mere ten million years or so after the dinosaurs died out.
These early bats, such as
Archeonycteris, Icaronycteris, Hassianycteris,
and
Paleochiropteryx,
were very similar to their modern counterparts—smallish bats about the size of our present-day North American bats. This doesn’t mean, of course, that bats didn’t evolve from flightless ancestors; rather, it simply means that we haven’t yet—and may never—find their intermediate ancestors. Most bats are, after all, very small, fragile creatures with delicate bones, which doesn’t make them the best of subjects for fossil preservation. Also, most of the very early bats were in tropical regions, where decay takes place with astonishing rapidity and there’s not much of the sedimentation needed to preserve fossils.
There is evidence of evolutionary processes at work in these earliest bat fossils, however.
Icaronycteris
and
Archeonycteris
appear to be somewhat more primitive in ear and throat structures than
Hassianycteris
and
Paleochiropteryx.
Whatever the evolutionary path, bats developed a unique wing structure. Whereas birds and pterosaurs (or pterodactyls, if you wish) evolved with wings supported by the bones of the arm and a single finger, a bat’s wing is supported by the arm and
four
greatly elongated fingers. Thus the order to which bats—and only bats—belong is Chiroptera, Greek for “hand-wing.”
The bat’s fifth finger, or “thumb,” incidentally, far from being elongated in the manner of its other digits, is a small hook used for climbing or walking. Yes, even though flight is their normal mode of locomotion, bats actually do climb such things as cave walls and trees, and even walk along the ground on occasion when seeking food. Neither are bats helpless in the water, for competent observers have even observed them swimming.
Flexible, yet strong for their extremely light weight, the elongated finger bones form a perfect support system for the bat’s wings. The actual wings consist of a wonderful double membrane of skin, similar to very thin, pliable leather. These wings not only cover the elongated finger bones, but also continue rearward until they actually attach to the tiny hind legs. Another section of this membrane connects one hind foot to the other; in most species, this rear section of membrane extends back to the tip of the tail. In so-called freetail bats, however, the slender tail itself projects well beyond the tail membrane.
This design of a bat’s wing can be compared to that of an airplane. Just as an airplane wing has a thin skin of aluminum on the top and bottom, covering a network of ribs and struts to lend rigidity, bats have a skin covering over the top and bottom of their wing bones, with blood vessels and nerves in the space between.
The result of all this is that bats have a very large airfoil in comparison to their weight. In terms of human technology, this makes them somewhat analogous to the old-fashioned biplanes. A biplane’s very large ratio of wing surface to weight made it slow but highly maneuverable. In the same manner, bats are fairly slow fliers compared with many birds, but they have incredible maneuverability.
Have you ever watched
—really
watched—bats in flight? Few people have; most who view bats from time to time either fear and loathe them or at best give them only cursory attention. This is unfortunate, because bats are truly amazing fliers! My wife and I often sit on our patio at dusk to watch the “bat show.” The land slopes away steeply below our patio, so that bats at eye level and above are silhouetted against the evening sky. Thus we’re able to enjoy the well-nigh incredible maneuvers which these little fliers make in pursuit of their prey.
This leads us to the method that most of our native bats use while hunting. Although the expression “blind as a bat” is a common one, it’s at least as inaccurate as it is common. Different species of bat vary somewhat in the quality of their vision, but no bats are blind, and most actually see quite well.
However, when flying in the dark while searching for tiny insects, even excellent night vision has serious limitations. Instead, bats rely on a most remarkable system, similar to radar or sonar, known as
echolocation.
To describe this system in its most basic terms, a bat in flight emits highfrequency sound pulses, above the range of human hearing. When these pulses strike nearby objects, their “echoes” return to the bat, which, with its incredible hearing, identifies and locates these objects with uncanny precision. This “radar” system is so amazingly sophisticated that scientists still lack anything approaching a full understanding of it.
The eighteenth-century Italian biologist Lazzaro Spallanzani was the first to postulate that bats could navigate in total darkness through a mysterious sense connected to their hearing. His views were generally ridiculed until the 1930s, however, when Donald R. Griffin, a Harvard University bat biologist and researcher, confirmed Spallanzani’s beliefs and identified the mysterious sense as echolocation.
However, even though scientists are still learning about echolocation, they do know that it depends on two components, one physical and the other biological. In the physical component, a bat emits high-pitched sound waves. When these waves strike an object, they “echo”—that is, bounce back to be received by the bat’s incredibly sensitive ears. Then the biological component of echolocation takes over, as the bat translates this information with astonishing accuracy and rapidity into an aural picture of its surroundings.
Not only is each nearby object placed precisely in spatial terms, but its size and form are also evident to the bat. Thus a bat can instantly determine whether its system has locked on a human, a branch, a tiny mosquito, or a larger, slow-moving moth. Moreover, it is constantly assimilating this stream of information not for one object, but for all of the many objects around it. So remarkably rapid and precise is this echolocation system that a bat can fly through a maze of wires strung throughout a totally dark room!
Even this description, however, does a grave injustice to the astonishing complexity of a bat’s echolocation system. Imagine a jet fighter plane—a marvel of human ingenuity and technology—patrolling the skies through the impenetrable gloom of night. Constantly searching for a possible enemy, its radar sends forth radio waves at a relatively low frequency that return somewhat limited information but can “see” objects at long range.
Suddenly this lower-frequency radar strikes what might be an approaching enemy. As the distance between the planes decreases, the pilot shifts to radio waves of much higher frequency. Although these lack the long range of the earlier signal, they provide a much more detailed picture of the potential enemy.
An amazing human achievement? Substitute sound waves for radio waves, and insects for an enemy plane, and bats have been doing this for countless millions of years! In fact, bats that hunt by echolocation use
three
different systems, depending on the species of bat.
One system uses
constant frequency,
usually referred to as CF. A CF bat, as such bats are known, utilizes brief, intermittent sound bursts at a given frequency. A typical frequency for a CF bat might be 115 kilohertz. This, incidentally, is far beyond the range of human hearing, which extends only to about 20 kHz. So-called CF bats are found in Europe, Asia, and Australia.
Our North American bats use different systems, however. Some, like the southwestern myotis
(Myotis auriculos)
use frequency modulation and are known as FM bats. Bats using this method of echolocation emit bursts of sound that sweep through a wide range of frequencies in an astonishingly brief period. A typical signal from an FM bat might sweep from 100 kHz to 50 kHz in just two
thousandths
of a second! The FM signals that these bats use are the sound-wave equivalent of radio FM signals.
