Spider Monkey (Ateles)

Spider monkeys, like this young one in Bolivia's Madidi National Park, are dependent on their mothers for about ten weeks after birth.

Spider monkeys (of several species) live in the tropical rain forests of Central and South America and occur as far north as Mexico. They have long, lanky arms and prehensile (gripping) tails that enable them to move gracefully from branch to branch and tree to tree. These nimble monkeys spend most of their time aloft, and maintain a powerful grip on branches even though they have no thumbs.

These New World primates are social and gather in groups of up to two- or three-dozen animals. At night, these groups split up into smaller sleeping parties of a half dozen or fewer. Foraging also occurs in smaller groups, and is usually most intense early in the day. Spider monkeys find food in the treetops and feast on nuts, fruits, leaves, bird eggs, and spiders. They can be noisy animals and often communicate with many calls, screeches, barks, and other sounds.

Spotted Hyena (Crocuta)

While hyenas are known as scavengers, they also possess great intelligence and skill on the hunt. One strategy is for a single hyena to cause confusion in the herd, while the others in the pack pick off an older or weaker member and chase the rest away.

Spotted hyenas are famed scavengers and often dine on the leftovers of other predators. But these hardy beasts are also skilled hunters that will take down wildebeest or antelope. They also kill and eat birds, lizards, snakes, and insects.

In an increasingly overpopulated Africa, hyenas and humans come into frequent contact. In fact, the Maasai people of Kenya and Tanzania actually leave their dead to be consumed by hyenas. However, these intelligent and bold animals will raid food stores and crops and are blamed for many livestock and even some human deaths. In some areas they have been heavily hunted as destructive pests.

Spotted hyenas are the largest of three hyena species. Brown and striped hyenas are the other two. Although hyenas appear similar to dogs, they are actually more closely related to cats. They live throughout much of Africa and eastwards through Arabia to India. Spotted hyenas live together in large groups called clans that may include up 80 individuals and are led by females.

Squirrel (Sciuridae)

Tree squirrels, like this eastern gray squirrel, are seen in many parks, backyards, and forests throughout the world.

Squirrels are familiar to almost everyone. More than 200 squirrel species live all over the world, with the notable exception of Australia.

The tiniest squirrel is the aptly named African pygmy squirrel—only five inches (thirteen centimeters) long from nose to tail. Others reach sizes shocking to those who are only familiar with common tree squirrels. The Indian giant squirrel is three feet (almost a meter) long.

Like other rodents, squirrels have four front teeth that never stop growing so they don't wear down from the constant gnawing. Tree squirrels are the types most commonly recognized, often seen gracefully scampering and leaping from branch to branch. Other species are ground squirrels that live in burrow or tunnel systems, where some hibernate during the winter season.

Steller Sea Lion (Eumetopias jubatus)

"These animals are always yelling at each other," writes photographer Joel Sartore of the Steller sea lions on Alaska's Lowrie Island. Here, two females go nose-to-nose over a disputed bit of territory in a crowded rookery. Alaska's Steller sea lion populations have been in precipitous decline over the last 30 years, and scientists are at a loss to explain the cause.

Stellers are the largest of all sea lions and they have an appetite to match. These giant pinnipeds hunt fish, squid, octopus and, rarely, smaller seals. They are found off northern Pacific coasts from Japan to California.

Steller sea lion breeding is one of nature's great mass spectacles. When these giants thunder ashore, their favored beaches, called rookeries, disappear under their numbers. Young pups are sometimes crushed by the throng, unheeded by powerful males with only a single purpose in mind. Bulls (males) must establish and hold a beach territory in order to breed. Most do not achieve this until they are nine or ten years of age.

Sumatran Rhinoceros (Dicerorhinus sumatrensis)

Unlike its Indian and African cousins, the critically endangered Sumatran rhinoceros is covered with patches of stiff hair, most prominent on its ears.

The two-horned Sumatran rhinoceros shares the bleak distinction of world’s most endangered rhino with its regional cousin, the Javan rhino. The smallest of the rhino family, the Sumatran rhinoceros lives in isolated pockets in the dense mountain forests of Malaysia, Indonesia, and possibly Myanmar (Burma).

Sumatran rhinos are generally solitary creatures that feed on fruit, twigs, leaves, and shrubs. Like other rhinos they have a keen sense of smell and sharp hearing, and they leave a network of scented trails throughout the forest in order to find one another.

As the smallest rhino, they weigh about 1,760 pounds (800 kilograms), and grow to a height near 5 feet (1.5 meters) at the shoulders and 8 to 10 feet (2.5 to 3.2 meters) in length. Unlike most other rhinos, their hide, dark red-brown in color, is covered with patches of short, dark, stiff hair. The hair helps keep mud caked to the body, which cools the hide and protects it from insects.

Sun Bear (Helarctos malayanus)

Sun bears are so named because of the bib-shaped patch on their chests, which legend says represents the rising sun.

The reclusive sun bear, smallest member of the bear family, lives an insular life in the dense lowland forests of Southeast Asia.
Found from southern China to eastern India and as far south as Indonesia, sun bears, also called Malayan sun bears, take their name from the bib-shaped golden or white patch on their chest, which legend says represents the rising sun. They have a stocky, muscular build, small ears, and a short muzzle, which has earned them the nickname “dog bear.” Their sleek, black coat is short to avoid overheating in the tropical weather but thick and coarse to provide protection from twigs, branches, and rain.
Sun bears grow to only about half the size of an American black bear. Males, slightly larger than females, are about 5 feet (1.5 meters) in length and weigh up to 150 pounds (70 kilograms), a stature which suits their arboreal lifestyle and allows them to move easily through the trees. They have even been observed making sleeping platforms high above the ground out of branches and leaves.

Tapir (Tapiridae)

The prehensile trunk of the tapir has changed little in millions of years of evolution.

Tapirs look something like pigs with trunks, but they are actually related to horses and rhinoceroses. This eclectic lineage is an ancient one—and so is the tapir itself. Scientists believe that these animals have changed little over tens of millions of years.

Tapirs have a short prehensile (gripping) trunk, which is really an extended nose and upper lip. They use this trunk to grab branches and clean them of leaves or to help pluck tasty fruit. Tapirs feed each morning and evening. During these hours they follow tunnel-like paths, worn through the heavy brush by many a tapir footstep, to reach water holes and lush feeding grounds. As they roam and defecate they deposit the seeds they have consumed and promote future plant growth.

Though they appear densely built, tapirs are at home in the water and often submerge to cool off. They are excellent swimmers and can even dive to feed on aquatic plants. They also wallow in mud, perhaps to remove pesky ticks from their thick hides.

Tasmanian Devil (Sarcophilus harrisii)

This yawning Tasmanian devil was photographed at a quarantine facility in Hobart, Tasmania, Australia. The site monitors devils for signs of devil facial tumor disease (DFTC), a fatal, contagious cancer that over the past decade has decimated wild populations of the iconic Australian marsupial.

As comical as it is, the familiar Looney Tunes portrayal of a Tasmanian devil as a seething, snarling, insatiable lunatic is, at times, not all that far from the truth.

Tasmanian devils have a notoriously cantankerous disposition and will fly into a maniacal rage when threatened by a predator, fighting for a mate, or defending a meal. Early European settlers dubbed it a "devil" after witnessing such displays, which include teeth-baring, lunging, and an array of spine-chilling guttural growls.

These famously feisty mammals have a coat of coarse brown or black fur and a stocky profile that gives them the appearance of a baby bear. Most have a white stripe or patch on their chest and light spots on their sides or rear end. They have long front legs and shorter rear legs, giving them a lumbering, piglike gait.

Thomson's Gazelle (Gazella thomsonii)

In addition to running at high speeds, Thomson's gazelles also use a bounding leap, called "stotting" or "pronking," to avoid predators.

Gazelles are medium-sized antelopes found in Africa and in Asia as far east as Mongolia. There are some 19 different species of gazelles.

These grazing antelopes live in herds, which can consist of as few as ten or as many as several hundred animals. During the plentiful rainy season, thousands of animals can be seen gathering in large groups.

Gazelles typically frequent wide-open spaces and plains, where they browse on grasses, shoots, and leaves.

Open plains make them visible to predators like cheetahs or wild dogs, but gazelles are fleet of foot. The Thomson's gazelle can reach speeds of 40 miles (64 kilometers) an hour.

Some gazelle species eschew the grasslands for mountainous landscapes or even deserts. During the dry season some grassland gazelles will even take to the African bush in search of water.

Three-Toed Sloth (Bradypus variegatus)

The three-toed sloth's long claws are well suited to an arboreal life but hamper its mobility on the ground, leaving it vulnerable to predators.

The sloth is the world's slowest mammal, so sedentary that algae grows on its furry coat. The plant gives it a greenish tint that is useful camouflage in the trees of its Central and South American rain forest home.

Sloths are identified by the number of long, prominent claws that they have on each front foot. There are both two-toed and three-toed sloths.

All sloths are built for life in the treetops. They spend nearly all of their time aloft, hanging from branches with a powerful grip aided by their long claws. (Dead sloths have been known to retain their grip and remain suspended from a branch.) Sloths even sleep in trees, and they sleep a lot—some 15 to 20 hours every day. Even when awake they often remain motionless. At night they eat leaves, shoots, and fruit from the trees and get almost all of their water from juicy plants.