The Sloth Bear

Background on the Species

The sloth bear is a species of bear endemic to the Indian subcontinent that is thought to have evolved into it current form during the early Pleistocene Epoch approximately 1.8 million years ago (Bears of the World). Its name is misleading in that the sloth bear is not related to the two or three toed sloth species in any way. It is thought that perhaps the individual who initially named the bear took its haggard appearance and prominent claws to mean that it was in some way linked ancestrally to the sloth. However, the long, shaggy coat of the bear and its long claws are adaptations made by the species unrelated to the similar adaptations of the sloth to the cold weather and diet of the bear. There are two subspecies of the sloth bear: the larger Indian sloth bear (Melrusus ursinus ursinus) and the Sri Lankan sloth bear (Melrusus ursinus inornatus) which has a shorter coat and smaller stature than its Indian counterpart. While both bears are endemic to the Indian subcontinent, they are found in different places in this region; the Indian sloth bear inhabits forested and grassland regions of India, Bhutan, Nepal, and Bangladesh while the Sri Lankan sloth bear is only found on the island of Sri Lanka.

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Taxonomic Classification

Phylogeny of Ursidae based on mitochondrial DNA analysis
Source: Yoganand, et al

Like most species, the sloth bear has been classified and re-classified over the years as more and more is learned about the species. Initially, the bear was given the taxonomic name of Bradypus ursinus meaning "bear-like sloth," however, it was soon realized that although the bear bore a striking resemblance and shared characteristics such as its shaggy coat and missing upper incisors with the sloth, it was a member of the bear family; as a result, it was placed in the genusUrsus. However, DNA and phylogenetic research revealed that the sloth bear had diverged from the sun bear, brown bear, polar bear, American black bear, and Asiatic black bear 12 million years before present and, therefore, was given its own genus Melursus (Yoganand, 2008). 

Physical Appearance

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The sloth bear is unique in its appearance standing out amongst other bear species with a distinct snout and thick coarse fur. The snout of this species of bear is longer and less hairy than those of other bear species. This is likely an adaptation to accomodate a diet of mostly insects. In addition, the sloth bear as the unique ability to close its nostrils in order to avoid inhaling dirt whilst scavenging for insects on the forest floor. These bears can extend their lips beyond their nose and typically lose their two upper incisors by the age of two in order to allow them to suck insects off the ground. This sucking sound is extremely loud being able to be heard up to 300 meters away. The coat of the sloth bear is typically long and shaggy however this varies by season; its hair is the longest behind its ears and at the back of its neck. Its long hair gives the bears the appearance of being much larger than they actually are. They are about 2-3 feet in height at the shoulder and weigh an average of about 220 pounds as adults (Yoganand, 2006). Sloth bears have an off-white or yellow v-shaped marking on their chests typically only seen if the bears stand on their hind legs. The front legs of the bears are curved inwards and webbed in addition to having 3 inch claws - all useful adaptations to digging for ants and termites. Although not considered by most to be the most charismatic of the bear family, the sloth bear's unique appearance reflects the useful adaptations the species has made to fill its specific niche in its environment.

Behavior and Diet

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Sloth bears, like most members of the family Ursidae, are solitary creatures often only coming into contact with others of the species while mating. Despite this trend, some adults have been known to travel in pairs with adult males being gentle with cubs. A unique characteristic of this species is the carrying of cubs on the mother's back until they are able to keep up with the adults. These bears are generally nocturnal however, females with cubs commonly are most active during the day in order to avoid predators active at night. Another possible reason why these bears were given the moniker they were was because of the slow, ambling gaite of the animals. Although they may look clumsy to observers, these bears can run faster than the average human and are extremely agile climbers. However, they do not generally climb trees when startled due to the high number of predators in their habitat that can also climb trees extremely quickly. They are also excellent swimmers and have been known to enter water to play. Although these bears are not generally aggressive, they may fight for food if presented with a confrontational opportunity. Mating season varies depending on location with females typically giving birth to 1-2 cubs (Bears of the World). The cubs are born blind only opening their eyes after 4 weeks and walking at about 1 month. The cubs stay with their mother until between 24 and 36 months of age. The diet of sloth bears consists mainly of termites which they are experts in hunting with adaptations to finding and digging them up. They are the only bear species adapted specifically for myrmecophagy, or ant and termite eating. They rarely prey on other animals and do no congregate in feeding groups as do other members of the family Ursidae. They supplement their diet of ants and termites with fruit and plant matter. 

Source: http://www.bearsoftheworld.net/images/bears/sloth_bear_02.jpg

Range and Habitat

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The Sloth Bear is endemic to the Indian Subcontinent historically inhabiting India, Bangladesh, Sri Lanka, Nepal, and Bhutan. They have a wide range of habitats including wet or dry tropical forests, savannas, scrublands, and grasslands. They are typically a lowland species remaining below 1,500 meters although they have been known to live as high as 2,000 meters in the Western Ghats region (Garshelis, 2008). In areas where the daytime temperature is hot, the bears will typically retreat to thickets, tree cavities, or rock outcrops to avoid the heat and maintain a nocturnal lifestyle. In Nepal and Sri Lanka, sloth bears are known to avoid human populations and therefore have little of an effect on cropland in those regions. Conversely, sloth bears in India frequently raid agricultural lands as a result of human encroachment on their territory. Sloth bear ranges are relative small in comparison to other bear species as a result of their different diet. While all other bears are predominantly carnivores typically requiring large expanse of land to hunt large prey, sloth bears' myrmecophagous diet allows the species to have much smaller range requirements as they do not need to go far to find what they are looking for.

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Status

The IUCN classifies the sloth bear as a vulnerable species as of 1996. Before 1990, not enough data was available to determine the status of the bears but following a study conducted by the IUCN in 1990, sloth bears were listed as vulnerable on the Red List. It is estimated that only about 20,000 bears are left in the wild with less than 10,000 of those being mature adults. Additionally, evidence suggests that as a result of range reduction, the population of sloth bears has decreased 30-49% in the last 30 years (IUCN, 2011). Habitats in Bangladesh are under particular pressure as the bears in this region inhabit the lowland areas often occupied by human populations. It is unknown whether or not the bears have gone extinct from this part of their range.

Source: Yoganand, et al

Threats

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Sloth bears face many different threats in its natural habitat on the Indian subcontinent. The small body size and adaptations to accomodate its diet has resulted in a less ferocious bear than typically imagined. Tigers and leopards are known predators of the sloth bear generally attacking the bears from behind and much more likely to attack bears with cubs than bears without. Despite its natural predators, habitat loss is the largest threat to sloth bear populations in the wild. Population growth in this region of the world has been exponential in the past decade with numbers growing at the second fastest rate in the world. Resultant of this rapid growth, expansion into formerly untouched land has become common place. Sloth bears are being pushed onto smaller and smaller plots of land that are unable to sustain large numbers of the solitary animals. Additionally, as the fringe of civilization approaches sloth bear habitat, the bears are coming into contact with human populations more frequently than ever before resulting conflicts that typically end badly for the bears. Attacks on humans may end in destroying the bear. The encroachment of humans on sloth bear ranges includes building roads through habitats, establishment of monoculture plantations, settlement of refugees, and expansion of agriculture. All of these actions result in smaller and less suitable habitats for sloth bears thus reducing their numbers in the wild. Another issue the bears face is poaching - male parts of bears are thought to be an aphrodisiac in some Asian cultures, bones, teeth and claws are used to ward off evil spirits, and bear fat and gall bladders are used in medicines. Sloth bears are considered to be pests by some communities justifying killing the bears by saying that the they are killing livestock or threatening the human population of an area.

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India's Dancing Bears
This cruel tradition in India began during the 16th Century and persisted for over 400 years. Cubs less than a year old were taken from their mothers had ropes or chains forced through their noses and most of their teeth removed without anaesthesia and then were starved and beaten by their trainers trying to teach them to "dance." They were used as a street acts often seen on the sides of roads with their owners pulling on the ropes attached through their nose to perform.  Often, these bears did not live past 8 years, less than one-third a sloth bear's typical lifespan (Kirby, 2003). Fortunately, this practice was outlawed in 1972 by Parliament under the Wildlife Protection Act and the last dancing bear was freed in 2009. This is a success story for conservationalists and animal advocates all over the world.

Satellite Imagery of Sloth Bear Range in India and Bangladesh

Data Collection

Data and images were obtained from the Maryland Land Cover Facility using Landsat 7 satellite's Enhanced Thematic Mapper Plus (ETM+) sensor. The images are 30 x 30 meter resolution with a swath width of 185 kilometers. Bands 1-8 were downloaded for the purposes of this analysis and layered in particular fashions in order to provide a broad scope of analysis of the images. In this comparative study of Indian and Bangladeshi environmental conditions, images of the two countries will be analyzed in order to determine the most suitable habitat for the sloth bear. Additionally, policies such as the setting aside of land for nature reserves collected from ProtectedPlanet.net will be used to determine future conservation efforts of the bear species on the Indian subcontinent.
 

Images for the sloth bear range in India were acquired from the Orissa region of India on the Eastern edge of the subcontinent. The yellow border outlines the limits of the region of India and the transparent red square is where the images were obtained by Landsat 7 in November of 2011. 

Images for the sloth bear range in Bangladesh were taken by Landsat 7 in the northwestern region of the country near the border. The images were acquired in November 2000. 

Data Processing
The Visible

These images were created by layering the visible bands 1,2,3 (Red-3, Green-2, Blue-1) to create a visual depiction of what the areas look like from space to the naked eye. 

The first image is of India over the Orissa region of the country. The terrain is variable with patches of dense forest interspersed with rocky areas. This coastal habitat is home to a population of sloth bears who thrive in the forested areas. The bears tend to avoid coastal areas so their numbers nearer to the coast. Additionally, coastal areas tend to be more heavily developed and populated. The visible bands do not provide many levels of analysis other than what can be seen by the naked eye. It does, however, provide a useful reference for other levels of analysis such as the use of infrared bands and an NDVI index. These avenues will be explored in more detail.

The image taken of Bangladesh differs greatly from the previous image of India. One of the main differences in the visible signs of deforestation that are apparent in this image. The region appears to be sparsely vegetated with a very small amount of heavily forested areas making it an unsuitable habitat for a sizable sloth bear population. As is true with most of the members of the bear family, sloth bears are solitary animals who require a relatively large range that typically does not overlap very much with the range of others of its kind. Although signs of human settlement or development are not apparent, it is obvious that humans have had an effect on the landscape of this study site. These effects become even more apparent with further processing and analysis using different bands and indices of forest health.

The Infrared

The second images layers the red, near-infrared, and mid-infrared bands (3,4,5) in a specific fashion (Red-4, Green-5, Blue-3) produces the following images.

By using infrared bands, the vegetative composition of the region can be better understood. The dark orange areas correspond with the densely forested areas seen in the visible light image and therefore represent areas of high vegetation cover. Bodies of water are appropriately colored blue. The less densely areas are the grey-green color. The bears would most likely be found in the areas appearing as bright orange as they prefer to inhabit areas with high forest cover providing them with the resources and protection required for their survival. As can be seen in this image, the large expanses of forested areas in the Orissa region of India provides plenty of habitat possibilities for the solitary sloth bear making it a suitable environment for a sizable population of the species. 

Conversely, this highly deforested region of Bangladesh is not the optimal environment for the sloth bear as its forests have been removed and have not yet been able to grow back. This can be seen in the large extent of this area that appears in the grey-green color. The amount of orange colors denoting regions of dense vegetation is far less than the previous image and also very fragmented. Disconnected forest does not help in sustaining large populations of species as they are not allowed the space or range to properly distribute themselves. These images taken in relatively close proximity to each other differ greatly from each other as a result of policies protecting certain regions in India and the lack of these same policies in Bangladesh.

Normalized Difference Vegetation Index (NDVI)

The third images show the Normalized Difference Vegetation Index (NDVI) for the study region in Orissa, India and northwestern Bangladesh. This index is used in remote sensing to determine the amount of live vegetation in an area. Colors were assigned using color theory to ensure that the pattern of vegetated and non-vegetated land can be clearly understood with dark green depicted areas with an abundance of live vegetation and sienna colors areas with low levels of live vegetation. Essentially, NDVI gives the level of "greenness" of an area by combining the infrared and red bands to produce the amount of photosynthetic activity in an area. It is calculated by subtracting the visible light from the near-infrared and then dividing this number by the number produced from the near-infrared added to the visible. This results in a value between 1 and -1 with the former representing areas with high levels of photosynthetic activity and the latter areas with low levels. These numbers are assigned colors in ENVI to depict the level of greenness that particular region. 

India shows signs of live vegetation in the same areas with dense forests in the image containing the visible bands as well as the infrared image telling the same story. As you approach the coast, the amount of live vegetation declines steadily before reaching the ocean seen in blue. Also, a unique marine area is seen near the coast of Orissa providing a habitat to many different types of species. Typically, however, the sloth bear would not be found near these areas because of the brackish water and the lack of resources the species requires to survive in the wild. Also, the marshy land is not a suitable environment for the bear's main food source ants and termites. This fact alone disqualifies this marine area as a suitable environment for the sloth bear.

Bangladesh proves to be a much less suitable habitat for the forest-loving bears appearing to have far less area of live vegetation. The amount of photosynthetic activity is drastically less in this area as seen in the lack of large regions of the dark green color; the areas with dark green are extremely fragmented. Additionally, the sienna color is seen in patches throughout the study area representing areas with extremely low levels of live vegetation and subsequently, areas that are unsuitable habitats for the sloth bear. The lack of photosynthetic activity is resultant of deforestation in the area - as all the trees in the region are removed, the photosynthetic activity will inevitably decline. 

Protected Areas

This image uses bands 1-3 (visible) to depict the Orissa region of India overlaid with protected areas in this part of the subcontinent. The red outlines areas set aside by the Indian government as nature reserves strictly dedicated to the preservation of species in this area. One of the reserves is located on the coast surrounding the delicate marshlands which provide habitats for a large number of the world's species and are important breeding grounds for several endangered bird species. Noticeably, three of the reserves are circular in shape. This shape has been determined to be the optimal design strategy for nature reserves based on the concept of island biogeography. In this line of reasoning, decreasing the amount of edge and increasing the amount of interior area. As a result of this line of thinking, many of the nature reserves around the world are round in shape. The data for these protected areas was obtained from ProtectedPlanet.net, downloaded as shapefiles, and then overlaid onto the image of India in the visible bands. Sloth bears would thrive in the two circular reserves located in the densely forested protected areas located in the northwestern part of Orissa.

This section of Bangladesh appears to have only 2 protected areas in the study area. Additionally, the larger of the two appears to be deforested making it unsuitable for many of the species that have adapted to heavily forested areas in this region. It should also be noted that the design of these habitats does not optimize the amount of interior space as the reserves in India did. The irregular borders of the protected areas do not follow the guidelines for creating successful reserves. The sloth bear would have trouble finding the resources it requires in this protected part of the country and would therefore have a hard time surviving despite the measures taken to protect species in this region. This image was processed in the same way as the Indian image with shapefiles downloaded from ProtectedPlanet.

Conclusion

Sloth bear distribution on the Indian subcontinent has varied over time as human development encroaches on the species territory and deforestation threatens the health of the remaining forest. Analyses of these two different regions reveal the reasons why sloth bears remain in the areas that they are found today. India has the largest population of the species simply because it has the largest amount of land to allow the solitary species to distribute themselves as well as having the protection needed to maintain its numbers enforced by the government of the nation. Conversely, Bangladesh's lack of policy and rapid human development has left much of the suitable habitat for the sloth bear deforested or occupied by the human population. 

Satellite imagery was used to analyze the amount of deforestation as well as the state of the remaining forest cover in two study sites - one in India and the other in Bangladesh. These two areas presented very different landscapes despite their close proximity to each other. India has taken great measures to ensure the biodiversity of the nation is preserved. As a result, sloth bear habitat continues to thrive and allow the bears to continue their presence in this part of the world. Bangladesh was, historically, a region where sloth bears could be found. However, as a result of rapid deforestation and lack of protected areas, sloth bears are no longer found in the country. The differences in the two countries can be seen from the images acquired by the Landsat 7 satellite. The levels of analysis including infrared, normalized difference vegetation index, and overlay of protected areas in the regions paints a picture of what the state of these areas is. 

Future policies for the protection of the endangered sloth bear should include the preservation of vital habitat of the species including densely forested areas on the Indian subcontinent. With these measures in place, hopefully the species will act as an umbrella species protecting other organisms in the same area. Forests provide habitat for hundreds of thousands of the planet's species so, in protecting these vital habitats, many thousands of species can be preserved. Sloth bears inhabitat tropical and sub-tropical latitudes in some of the lushest habitats in the world. It is critical that these forests are maintained for the future of the species that require them for survival. The most effective way of going about the protection of these areas is through policy - that being said, more policies protecting the environment need to be instituted to protect these precious floral and faunal species.