Sloth Bears
by John Seidensticker
Sloth
bears are not sloths. They are bears that live on the Indian
subcontinent including the island of Sri Lanka. The various
species of sloths live in South America. So why the name "sloth
bear?"
Much 18th-century Western knowledge about tropical animals came from the study of specimens sent by curious naturalists from distant ports-of-call to Europe’s great museums. Consider the wonder, and subsequent confusion, when a Mr. A. Seba opened a shipping crate, newly arrived in Europe by sailing ship from Ceylon (Sri Lanka) by way of a landfall on the east coast of South America. This was the normal route in the 1700s for ships of the Dutch East India Company travelling from Asia to Europe around southern Africa’s Cape of Good Hope.
Mr. Seba was impressed with his new specimen’s long, curved, ivory-colored claws, similar to those possessed by sloths, so he called this a sloth from Ceylon when he described it in 1734. D. P. Erdbrinek, the taxonomist who ferreted out this story, believed Mr. Seba may have been victim of a seafarer’s prank because the "specimen" turned out to be "…the mutilated parts of an Aswail [sloth bear] from Ceylon together with parts of a [South American] three-toed sloth…." This error was not soon corrected and was even compounded when other early taxonomists, confused about the specimen’s origins, thought it was a creature from Africa.
The first valid scientific description, by George Shaw in 1791, called this strange creature Ursine Bradypus. Ursine means bearlike, while Bradypus (literally, slow foot) is the genus name of three of the species of sloths. Shaw thought that the bear was a sloth, primarily based on the shared characteristic of lacking the two first upper incisors. Time, and additional specimens, eventually revealed the true taxonomic relationships, but the confusing common name remains the English tag for this mysterious bear.
What is the story with those long, curved, ivory-colored claws and missing upper incisors that, coupled with a shaggy black coat, nearly naked nose, and protrusible lips, so befuddled those early scientists? Our studies of wild sloth bears show that, unlike sloths, which eat leaves while hanging high in rainforest trees, sloth bears are specialized feeders on ants, termites, bees, and, seasonally, fruits. They use their long curved claws to carefully dig out and open ant and termite nests on the ground, then hurry to suck up the insects by sucking and blowing, a process that sounds like a jack-hammer and is made possible by those protrusible lips and missing incisors. These bears also use their claws to climb tall trees to reach bees’ nests, rich in honey and bee larvae. The nearly furless brown nose doesn’t get gummed-up with the defensive excretions of termite soldiers, while the long shaggy coat wards off insect attacks.
One endearing sloth bear trait is that the female carries her young cubs on her back. (This is a behavior characteristic of other ant-eating mammals such as the South American giant ant-eater.) They do so presumably because a female must cover long distances each night as she travels between the many ant and termite nests she must visit to obtain enough to sustain her and her young. (The average litter size is 1.5, equally divided between litters of one or two.) She can linger only so long at each nest, blowing and sucking in ants or termites, before the ant or termite soldiers amass and attack in sufficient numbers to make a longer stay unpleasant.
Sloth bears also live where other large dangerous carnivores live: tigers, leopards, and wild dogs on the subcontinent and leopards in Sri Lanka. These large carnivores readily kill sloth bears if they can catch them, and riding on the mother’s back seems a good way to keep cubs close during the nightly search for ant and termite nests.
I met an adult female sloth bear one day while radiotracking tigers from elephant back in Royal Chitwan National Park in the lowlands of Nepal. She was 30 feet up in a tall bombax tree, out on a limb, knocking pieces of a bees’ nest to the ground. Her cubs were below, eating the wax, honey, and larvae. She immediately saw and smelled us and "woffed" to her cubs, who rushed off into the 20-foot-tall grass beside the trail. Then she descended from the tree and charged the elephant, only veering off into the grass when my elephant man launched the elephant into a dead run straight at the bear.
There were several lessons in this flash encounter, not the least of which was that an immediate offensive move is sometime the best defense. But why not have the cubs climb in response to a perceived threat? I have often seen American black bear females send their cubs up trees when they sensed a threat. The answer may be that sloth bear cubs and even females in a tree remain vulnerable to predators, especially to leopards, which readily climb.
The threat posed by these large carnivores may also explain another curious sloth bear habit. We know from our Zoo sloth bears that they can live quite well on a "typical" bear diet. Black and brown bears readily eat carrion of large ungulates such as deer and elk, especially in the spring when animals that died over the winter are exposed. However, wild sloth bears usually do not feed on carrion. In sloth bear country, a big dead deer usually belongs to a tiger or a leopard—an animal to be avoided.
We know little about the status of the sloth bear on its home ground. My colleague Andrew Laurie and I studied sloth bears in Chitwan National Park in the early 1970s. Fifteen years elapsed before Anup Joshi and his advisors David Garshelis and David Smith from the University of Minnesota took up the challenge of studying these bears, also in Chitwan. These investigators learned that sloth bears can adapt their diet to changing food availability. Termites were more dominant in their diet and fruits less so than they were 20 years before. In that time, most of the livestock had been removed from the park and as a result the park’s plant composition changed, with fruiting plants declining in number. The bears appeared to respond by eating more termites.
Half way around the world from my Nepal field site, I was at the National Zoo when a sloth bear cub was born here. The cub’s emergence from the den when it was about three months old was a cause for much celebration. At the Zoo I watched the mother teach her cub proper back-riding etiquette and listened to the short-range "chuffing" calls used between female and cub. The cub rode about on her mother’s back, hip, and shoulder. If the cub seemed off-center, its mother shook vigorously, occasionally flipping the cub all the way over her back; when the cub was too far forward, its mother elbowed it back. To get aboard, the cub stood on its hind legs, grasped the female’s long fur with its forepaws, and scrambled on.
The first sloth bears came to the Zoo in 1898; since then, 24 sloth bears have lived here for various amounts of time. Eleven litters of cubs have been born here, the last in 1994. In 1998, we acquired a female named Hana, born in Warsaw, Poland, in 1994, and here on a breeding loan from the Toledo Zoological Gardens. The Toledo Zoo imported her because there are only 40 sloth bears in the North American zoo breeding program.
Conservationists believe sloth bears are threatened by habitat loss and change. But until recently the only field studies have been in Chitwan. The rich, productive alluvial floodplain of the Rapti River, which flows through the Chitwan Valley, is not at all like most of the remaining sloth bear habitat. More than half of the forested wildlife habitat left on the Indian subcontinent is tropical dry forest, a highly seasonal habitat with low productivity compared to Chitwan. In October 1998, I visited this habitat in central India’s Panna National Park, where A. J. T. Johnsingh and K. Yoganand are now studying sloth bears. Johnsingh, who worked with me in 1981 as a FONZ-supported post-doctoral fellow, is head of the wildlife faculty at the Wildlife Institute of India. Yoganand is his graduate student.
Yoganand, Yogi to his friends, is studying the behavioral ecology of the sloth bear for his doctoral dissertation. By comparing feeding, ranging, and other behavior of sloth bears in this relatively poor, dry habitat with the bear’s behavior in the rich Chitwan site, he will be able to assess the limits of the bear’s adaptability in the face of the massive environment transformation that is going on through much of the forested areas of India, Nepal, and Sri Lanka.
Yogi’s studies are ongoing but he has learned that his bears are dependent on harvesting a very few species of driver ants, even though many more ant species live in Panna. The key to understanding sloth bears in this habitat lies first in understanding why they focus their foraging efforts on just a few ant species and then in understanding the ecology of driver ants. The factors that limit the distribution, size, and growth rates of ant colonies, and the frequency and extent to which the colonies can be harvested by sloth bears will also limit the distribution and density of sloth bears.
Before they are finished, these scientists plan to survey much of the remaining tropical dry forest, in conjunction with Indian Forest Department officers, to determine the sloth bear’s current distribution and assess the threats it faces. The situation is not promising. Most of India’s tropical dry forests are deteriorating from excessive cattle grazing and the extraction of fodder and other forest products by people. What is promising for sloth bears is that Indian and Nepali wildlife scientists are looking into their survival needs in detail. With this information, workable conservation plans for specific regions and habitat types can be crafted and implemented. I find this trend encouraging. The sloth bear and all the magnificent wildlife of the Indian subcontinent will benefit.
John Seidensticker is Senior Curator at the Smithsonian National Zoological Park.
ZooGoer 28(2) 1999.
Copyright 1999 Friends of the National Zoo.
All rights reserved.
Photo by Jessie Cohen, NZP Staff Photographer
