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"Despite the efforts of many earnest and life-affirming people to persuade me that the vampire bat is our friend and that Native Americans enjoyed true harmony with Brother Wolf, I have never quite overcome the gut feeling that fear of nature is normal....It can also be pleasurable....What I really find creepy and wonderful about nature are not its great terrors, but its weird, unsuspected minutiae...for instance, that some sharks practice sibling cannibalism in the womb, or that a mole will paralyze earthworms, ball them up in a knot, and seal
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"Despite the efforts of many earnest and life-affirming people to persuade me that the vampire bat is our friend and that Native Americans enjoyed true harmony with Brother Wolf, I have never quite overcome the gut feeling that fear of nature is normal....It can also be pleasurable....What I really find creepy and wonderful about nature are not its great terrors, but its weird, unsuspected minutiae...for instance, that some sharks practice sibling cannibalism in the womb, or that a mole will paralyze earthworms, ball them up in a knot, and seal them away in individual cells in the walls of its chambered mound, still living, to be eaten at leisure. I am captivated by the sight of a keyhole limpet...[which] carries a sort of vicious pet under its shell, like an old lady's lap dog."—From Every Creeping Thing
In this sequel to Spineless Wonders, Richard Conniff once again explores the tangled connections between human beings and animals (this time mostly vertebrates). His adventures take us from an island in the Gulf Stream, where a man devotes his life to the devilbird, to provincial England, where bloodhounds and riders on horseback hunt down a human being for sport.
With his characteristically offbeat approach, Conniff focuses on some of the least huggable members of the animal world— porcupines, snapping turtles, cormorants, bats, mice, moles. Through their lives, Conniff introduces us to some of the strangest behaviors on earth. We meet sharks that practice sibling cannibalism in their mother's womb, bats that delight in a sybaritic "disco mating strategy," and five-hundred-pound grizzly bears that gorge themselves on moths in August. Every Creeping Thing is a fascinating, comic tour through the far side of the animal kingdom.
|Introduction: Healthy Terror||3|
|Days of Torpor, Nights of Sloth||18|
|The Devilbird of Nonsuch||31|
|The Cave of the Bats||41|
|Looking for Mr. Griz||70|
|What's Nice? Mice||90|
|Acting Like Animals||118|
|A Mouse Like a Spear||128|
|Sharks, Part One: Great White Hunter||142|
|Sharks, Part Two: How Sharks Got into Such Deep Soup||157|
|A Porcupine Would Rather Be Left Alone||173|
|Notes from the Underground||181|
|Sleeping with Snapping Turtles||215|
|Epilogue: Black Hound||230|
Days of Torpor,
Nights of Sloth
The first time I saw a sloth, in a small and sparsely furnished cage at the National Zoo in Washington, D.C., it took me several moments to spot the thing: a motionless blob of fur clinging to a bare tree branch.
"It's a fake," a teenager advised me. "Fake something or other. There are two of them."
"They're gorillas," another teenager ventured. "Little baby gorillas."
"Then how come they don't move?" said the first teenager.
The second teenager consulted the small sign posted in a corner. "Maybe it's a leaf-nosed bat," he said, reading the name of a species said to be in residence. But the idea of a bat the size of a small dog and leaf-nosed to boot was so unsettling that after a brief pause all of us descended as one on the sign. "Oh," said the second teenager, "they're sloths."
"What? Those big ugly things?"
"Yeah. It says right here. Two-toed sloths."
Full of doubt, his companion replied, "I thought sloths were supposed to be extinct."
Pity the sloth. It is an animal perpetually misunderstood and reviled by the human species. These inoffensive mammals, which pass most of their lives thirty to ninety feet up in the rain forests of Central and South America, have been called "normal morons," "chronic pacifists," and even "hanging animal baskets." Georges-Louis Buffon, the eighteenth-century naturalist, listed among their chief attributes "slowness, stupidity and habitual pain," and added that with even a single additional defect, sloths would cease to exist. Indeed, the sloth's very name is a deadly sin. Says the Bible: "Slothfulness casteth into a deep sleep; and an idle soul shall suffer hunger."
But there is a paradox here. The sloth truly enjoys a deep sleep ten to fourteen hours a day, and it is by definition idle. Some sloths are so lethargic as to be utterly unmoved by gunshots at close range or by the presence of cats, eagles, or other common predators. And yet sloths survive, lazing in the upper branches of the jungle, while quicker, keener, more industrious animals around them fall victim in the daily struggle. As to hunger, the sloth's stomach is disproportionately large. Together with its contents, it may make up a quarter to a third of the animal's weight. And it is usually full. Sloths have the good sense to survive largely on leaves, and the supply is abundant. They do not often suffer hunger. The sloth is, in short, an affront to all our notions about the predatory jungle, and about life itself.
Shortly after my zoo visit, in search of a somewhat more informed point of view on these enigmatic creatures, I traveled to one of the places they call home, Barro Colorado Island in Panama. There are probably ten or more sloths in every hectare or four or more per acre on this island reserve, which is maintained by the Smithsonian Tropical Research Institute. But naturalists may work for months without noticing one. An exception is Bonifacio de Leon, known to other naturalists on the island as "Boney," who had been described to me as possessing an almost supernatural ability to locate sloths. I found him at his workbench, with the skulls of monkeys and three-toed sloths hanging from monofilament overhead. He agreed to take me on his morning tour, and after he'd put on a silver hardhat and taped his pant legs shut at the ankles as a precaution against ticks, we set off.
Five yards into the forest, he stopped, pointed, and said, "Perezoso" Panamanians call the sloth gato perezoso, or "lazy cat". When it became apparent that I could see nothing, Boney seized me by the shoulders and fixed me at the proper angle of vision. Still nothing. He plunged into the undergrowth, and I followed him fifty feet in, past a dozen substantial intervening trees. Just as he was about to start climbing, I discerned a three-toed sloth sixty feet up. At that moment, it was scratching its butt, rather ineffectively.
Back on the trail, Boney pointed out an assortment of wildlife, with which he communicated by sucking noisily on his wrist, by smacking his lips against his fist, and by humming on a torn off piece of leaf. Some of the creatures he addressed were visible--a parrot, a toucan, an anteater. Some were merely audible--the capuchin monkeys crashing through the treetops. A few--the sloths--seemed neither visible nor audible. Boney helped me in my obtuseness. When I failed to perceive a two-toed sloth sleeping fifty feet up in a hammock of vines, he picked out two vines hanging down from the canopy and hauled on them like a bell ringer in a church tower. The sloth stirred and became apparent, moving off like an upside-down cat that is slightly peeved at being disturbed. "Perezoso," Boney explained.
I consoled myself with the thought that even Gene Montgomery, then a vertebrate ecologist at the Smithsonian Tropical Research Institute, had a hard time spotting sloths. Throughout the 1970s, Montgomery and a colleague, Mel Sunquist, conducted the first methodical study of sloths in their native environment. The two of them, and sometimes Boney, too, climbed trees to capture animals for observation, fed glass beads to captives to measure digestive flow, strapped radio collars on free-roaming individuals, tucked minitransmitters up the animals' backsides, and otherwise arrived at a detailed knowledge of the sloths of Barro Colorado Island.
Studying sloths requires patience above all watching them in action has been likened to reading War and Peace, but in Montgomery I did not find the phlegmatic, professorial "Dr. Sloth" I had been expecting. He arrived to meet me outside his office in Panama City at the wheel of a battered four-wheel-drive vehicle. Solidly built and ruddy-skinned, he wore a great walrus moustache and a characteristic facial expression of roguish glee. The first point he wanted to make about sloths--almost before we sat down--was that they are "nice animals." Or rather, three-toed sloths are nice, anyway.
The distinction matters, as he soon explained. The five species of sloth fall into two genera, whose scientific names are Bradypus which means slow-footed and Choloepus which means crippled. Montgomery pulled out a cardboard box full of animal bones in plastic bags. "That one's an anteater," he said, throwing a bag back and continuing his search. When he'd found suitable specimens, he demonstrated that the two sloth genera can be distinguished by the number of hooklike claws on their forelimbs; hence the common names two- and three-toed sloths. They are as different, he said, as cats and dogs.
Two-toed sloths, like the blobs of fur I'd seen in the zoo, are far and away the livelier genus. Compared with other mammals, two-toed sloths may seem dazed or drugged. But three-toed sloths in action can be compared only with plants, and even then, kudzu may be quicker. They move as if put into a trance and then filmed in slow motion. Indeed, Montgomery's predecessors in sloth research did not require radio telemetry. To test the mobility of the three-toed sloth in the wild, naturalist Hermann Tirler placed a plastic bowl on an animal's head one night. It was still there in the morning. Another time, he briefly kept a three-toed sloth as a pet: "One evening," he wrote, "we suddenly smelled something like a burning sloth, the odor coming from the neighboring room." The animal was half-asleep on a large electric bulb, with its rear going up in smoke, and according to Tirler, it wanted to stay there.
While climbing ninety-foot-tall trees, some of them too thick for a safety belt, Montgomery understandably came to prize the three-toed sloth for its immobility. It was a relatively easy matter to reach out with a noose at the end of an extension pole, pluck the animal from its perch, and lower it to the ground. Close encounters at that altitude were also not unpleasant. Even if a three-toed sloth were to rouse itself to attack, the only creature slow enough to suffer its bite would be another three-toed sloth. In any case, said Montgomery, it has no incisors and its bite is no worse than a somewhat leathery kiss.
The two-toed sloth, on the other hand, has sharp canine teeth and can make itself very unpleasant when threatened. Hissing, it swings an arm out to hook an adversary and draw it in toward its mouth. Montgomery showed me a knuckle on his hand that was once cut to the bone in this fashion. As if being bitten by a sloth were not embarrassing enough, he noted with chagrin that the animal was under sedation at the time. The two-toed sloth is also quick enough to run away when provoked. Montgomery recalled afternoons in which he climbed one ninety-foot tree only to have his quarry escape to the next tree over, then climbed that tree only to have the sloth escape to a third tree, and so on until "the air was fairly blue with strong language." Radio-tracking showed that two-toed sloths also do a considerable amount of traveling through the trees without provocation. Unlike three-toed sloths, they are strictly nocturnal, and on their nightly ramblings they may use their canine teeth to raid birds' nests; in captivity they also eat fruits and vegetables.
I suggested to Montgomery that if one compared the two kinds of sloths it might seem that the three-toed genus is more primitive, a less-advanced life-form. Not only is its lifestyle one of more profound torpor, but as Buffon suggested, it seems fragile, on the verge of extinction. No one has ever managed to keep a three-toed sloth alive in captivity on any diet. Montgomery regarded my suggestion balefully. On the contrary, he said, it was possible to argue that the more active genus is, in a sense, less perfectly adapted to its environment. The lazier, less aggressive three-toed sloth has advanced further into the sweet ecological niche of slothfulness. Every feature of these animals has evolved to make a leaf-eating, tree-dwelling life easier.
Besides being hard to reach, leaves are also difficult to break down into useful nutrients; their single virtue is their abundance. To exploit this resource, both two- and three-toed sloths had to make compromises, and it might well be said that they gave up everything else in exchange for a permanent meal ticket.
Muscle, for example. Maintaining muscle bulk requires more energy than a sloth can easily extract from leaves, so it gets by on about half the usual amount. The two-toed sloth weighs about ten pounds, the three-toed just seven, and only about a quarter of their body weight is muscle. Low body weight is an advantage; it allows the sloth to climb out on the slenderest branches, where it can harvest leaves at a leisurely pace, safely beyond the reach of most predators. But lack of muscle is also the reason sloths are so slothful. They simply don't have what it takes to go any faster. On the ground, where they seldom travel, sloths drag themselves along on their bellies. I saw several animals attempting this in captivity, on a concrete surface, and they looked like men dying in the desert just short of the water hole. But hanging under a branch requires little energy, especially as sloths can lock their hooklike claws in place and concentrate on the more important business of sleeping and eating. Their grip is so tenacious that, according to myth, they remain hanging in place even after death. At times, for want of an easier way to bring down a sloth, Montgomery had to saw off the branch to which the animal was attached. South American Indians who eat sloths sometimes bring them home in this fashion, with the branch over a shoulder and the sloth hanging off the end, riding indolently to its doom.
Immobility is otherwise a virtue for sloths. Their stillness makes them harder to see, and not being seen is really their best form of defense. All their extremities are adapted to crop the maximum area of surrounding leaves with the least possible movement. For example, said Montgomery, other mammals, even giraffes, have seven vertebrae in their necks. He showed me the skeleton of a three-toed sloth; it had nine. The three-toed sloth can bury its pestlelike head and neck in its chest or swing it back perpendicular to the spine to get at leaves behind its head. It can also rotate its head through three-quarters of a circle, and it does so regularly. One of the sloths Boney showed me on Barro Colorado kept looking slowly from side to side like a bewildered child in bottle-bottom glasses. Having settled into a verdant spot, with food all around, sloths do not, however, gorge themselves. They masticate slowly and, according to one source, take in only about one-seventh as much sustenance as a young fawn of the same weight.
In its quest to remain unnoticed, the sloth benefits not just from its immobility but also from its excellent natural camouflage. As my instinct for sloths became keener during my stay on Barro Colorado, I spotted one sitting in the crotch of a tree, arms folded across its chest, patiently waiting for nearby buds to burgeon. It resembled nothing more animate than a nest or a bunch of dead leaves. But as if this were not enough, I noticed that its pelt had a greenish tinge that blended in with the foliage. Montgomery later explained that three species of algae grow in its grooved, gray-brown hairs.
After immobility, the sloth's other great adaptation to leafy life is its gut. The eighteenth-century Irish author Oliver Goldsmith described the sloth as "the meanest and most ill-formed of all those animals that chew the cud." In fact, chewing the cud would take far too much energy to be of any value to a sloth. Instead, it allows the bacteria in its multichambered, ruminant-like stomach to do the work of breaking down cellulose into energy. No other animal devotes so great a portion of its bulk to digestion. One researcher described the sloth to me as simply "a big chemical factory, a fermentation chamber that moves around in the trees."
Despite the size of its stomach, the sloth digests need one say the word? slowly. It is a very regular animal. Montgomery and Sunquist found that three-toed sloths defecate and urinate approximately once every eight days, two-toed sloths slightly more often. This lethargic digestion may be due to the animal's inability to maintain a constant body temperature. It ranges from a high of 91 degrees Fahrenheit to as little as 75, and when the temperature drops to its daily low point, the chemical factory may simply shut down.
The sloth's toilet habits are remarkable. Its excreta are almost odorless and would probably not betray the animal's presence if merely dropped to the ground from fifty feet up. But when nature calls, the sloth always descends laboriously to the base of a tree. Hanging on to a vine with its forelimbs, in a position of extreme vulnerability to predators, the three-toed sloth actually digs a shallow hole with its stubby tail before emptying bowels and bladder. It then covers up its wastes with dead leaves, and climbs slowly back up into the canopy.
What makes this ritual even more bizarre is that it is the focus of intense interest among a vast group of specialized insects living in the sloth's hair. Sloths harbor nine species of moths, four species of beetles, six species of ticks, and other assorted mites, and receive frequent visits from itinerant mosquitoes and biting sand flies--altogether constituting a remarkable instance of the profusion and interdependence of tropical life. Researchers have gathered as many as 120 moths from a single sloth, and a record of 978 beetles, all of them waiting patiently for the sloth's weekly defecation, which is both a source of nutrition and an ideal site for egg laying. This population might seem even lazier and less demanding than the sloths on which they live. Adult moths, for example, sometimes break off their wings in the host's fur and remain contentedly sloth-bound for life. But the competitiveness among tropical fauna is such that some of the beetles and mites actually enter the sloth's anus to lay their eggs, gaining several days' incubation time on their less intrepid rivals. All this the sloth bears with equanimity.
The three-toed sloth spends several hours a day grooming, but with little effect on beetles or moths, which can be seen advancing in waves just ahead of the sloth's slowly probing claw. Montgomery believes the grooming is mainly intended to fluff up the sloth's hair and an underlying layer of fur for better heat retention.
The sloth is an excellent swimmer, and this, too, might be expected to have a discouraging effect on its insect friends. The leaves crammed into its gut give the sloth excellent buoyancy. I saw sloths swim more than a mile across Lake Gatun and the Panama Canal to get to and from Barro Colorado, and they manage both a creditable breaststroke and a passable backstroke. The French naturalist Marcel Goffart was moved by the same sight to rhapsodize: "Their arms work strongly, and their behind waggles elegantly. Gone is their sluggishness.... Gone is the usual laziness. The swimming sloth is beautifully easygoing." As to insects, the dousing does not bother them. They crowd up in the dry hair of the sloth's head and back, waiting out the trip like passengers on the Friday night ferry to Nantucket. Scientists can only speculate about why an arboreal mammal would have become such a good swimmer. But it is obviously a useful skill in flood-prone areas and also helps as a dispersal mechanism.
From swimming, we come to sex. Goffart presents sloth lovemaking as a sort of splendor in the jungle. He reports hearing about one affair that lasted two days, and of a second encounter, he writes: "They were locked in close embrace, ventre a ventre. No signs of fighting were evident. Several general muscle spasms were said to have taken place over a period of half an hour, not the least attention being paid to onlookers."
Alas, the only reliable eyewitness account comes from the National Zoo in Washington, D.C., and it is considerably less romantic. Sloths do, in fact, have sex face-to-face. Like humans, they form the "two-backed beast," and they do so while hanging from a branch. The female assumes the sloth's characteristic inverted position. The male, also inverted, works his way between her and the branch. Then he turns over until they are face-to-face, with the female becoming a sort of hammock. Here is one instance where humans might wish the sloth to be truly slow. But in the encounter witnessed by Larry Newman of the National Zoo, the male sloth made about ten misguided thrusts, finally achieved penetration, then finished off with three or four quick thrusts before withdrawing. Newman does not say whether the male fell asleep on the spot or at a polite distance. The female gave birth eleven months later.
The sloth's strategy of a long, leisurely life up to 40 years, and a low rate of reproduction has made it a remarkable success from Honduras and Nicaragua in the north to about Sao Paulo in the south. There is, however, one effective counter-strategy: take away its leaves. This is, of course, exactly what is happening as land-hungry people cut into rain forests in Panama and throughout the hemisphere. So far, most sloth populations remain secure in their environment. But along the Brazilian coast, less than 3 percent of the original rain forest has survived human habitation, and one sloth species, Bradypus torquatus, is endangered as a result.
Scientists know almost nothing about B. torquatus, the maned sloth. It possesses the fixed grin of other three-toed sloths, and a distinctive cowl of dark fur over its shoulders and down its back, which makes it look rather like an idiot prince. At the Poco das Antas Biological Reserve in Rio de Janeiro state, researcher Laurenz Pinder has begun radio-tracking maned sloths as part of a World Wildlife Fund project. But in the entire five-thousand-hectare reserve, with trained naturalists constantly on the lookout, only about fifteen maned sloths are sighted each year. So far, Pinder has put radio collars on just six animals. Outside the reserve, in the isolated pockets of rain forest surviving on the coastal strip between Sao Paulo and Bahia, the species is apparently even less common. One of Pinder's objectives is to discourage people from taking the animals as pets or from shooting them in the course of indiscriminate hunting.
The question of the sloth's eventual survival or extinction brings us finally to the matter of its supposedly abysmal stupidity. The idea that sloths are stupid, rather than merely simple, got its start centuries ago, when writers began repeating a myth about the animal's dietary ineptitude. According to Buffon and others, the sloth would climb a tree and gradually strip it of every available leaf. Then, being incapable of climbing back down, it would simply drop to the floor of the rain forest and drag itself off to kill another tree. A second myth was that sloths would eat the leaves of only a single tree genus, the Cecropia. Without it, as Buffon suggested, sloths would cease to exist.
But in their study on Barro Colorado, Montgomery and Sunquist found wonderful elegance in the way sloths harvest the jungle foliage. Though they are solitary animals, they have evolved a neat social system. Sloths in fact eat the leaves of at least ninety species of trees and vines, and different individuals prefer different species. Each sloth has a range of eight or so favorite trees and moves among them via the treetop network of vines. Thus several sloths can live in the same territory, not competing with one another but making such efficient use of the trees that they inhibit other animal species from moving in on their ecological niche. According to Montgomery and Sunquist, a square kilometer of healthy rain forest may contain seven hundred sloths and only seventy howler monkeys, their most numerous mammalian rival. The monkeys get all the attention, making a noise like a cruise missile whistling past one's earlobe. But it is the sloths who proliferate. The tropical canopy is packed with them. Evolutionary theorists have even speculated that the sloth's long-standing dominance in its niche may be the reason the New World tropics produced so few primates.
Sloths pass their dietary preferences on to their offspring. The infant which Montgomery described as "a round ball of fur, very soft, and with soulful eyes" spends its first six months or longer clinging to its mother's hair, learning to eat what she eats. In the process, by licking bits of leaves from around her mouth, it also picks up her mix of gut microorganisms, which are specific to her preferred list of edible leaves. Three-toed sloths in captivity have starved to death on a full stomach because they were fed leaves for which they did not have the proper digestive microorganisms. And when the mother turns her offspring out on its own, she gives it a part of her range to help it get through the first year, after which it must strike out into the world.
There is an admirable harmony in this way of life. By exploiting a variety of different trees, sloths avoid putting pressure on any single tree species. And in Montgomery's interpretation, they may actually cultivate their preferred trees. By burying their excreta at the base of the trees that feed them, they return about half of the nutritional value taken out in leaf eating.
This elegant system may be the reason sloths can get by on about one-tenth of the work load of other mammals their size. It is the reason sloths can spend their mornings dozing in the sun while the rest of the animal world wearies itself with the daily toil of getting and spending. Sloths have adapted perfectly to their environment. They have made themselves masters of digestion, champions of sleep, gurus of the pendulous, loafing life. They will survive in splendid indolence as long as humans do not destroy their habitat. And we're calling them stupid?