Rhinoceros
- CLASS: Mammalia (Mammals)
- ORDER: Perissodactyla
- FAMILY: Rhinocerotidae
- GENUS AND SPECIES: Diceros bicornis (black rhino), Ceratotherium simum (white rhino), Dicerorhinus sumatrensis (Sumatran rhino), Rhinoceros unicornis (greater one-horned rhino), Rhinoceros sondaicus (Javan rhino)
ABOUT
Ambassadors from another age: The rhinoceros looks as though it has lumbered into our time from some primeval era. Its heavyset body stands on sturdy legs like tree trunks. Its eyes peer from a massive head that tapers to that battering ram of a horn. In our imaginations, the rhino is the embodiment of brute strength. Yet most of the time this fearsome creature is content to browse peacefully on vegetation.
The rhino’s lineage is an ancient one—its ancestors walked the Earth 55 million years ago. One of these ancestors, the paraceratherium, was 25 feet (7.6 meters) long and 18 feet (5.5 meters) high at the shoulder, the largest land mammal ever known. Throughout the eons, close to 100 known rhinoceros species have existed. Today, only five species continue the line: two native to Africa and three native to Asia.
What all rhinos have in common are one or two horns, a broad chest, thick skin, poor eyesight, excellent hearing, and a fondness for rolling in the mud. Their thick skin acts like protective plating but is sensitive, as the blood vessels are close to the skin’s surface, and can be easily scarred. Rhinos soak in mud or roll in dust as protection against sunburn and insect bites.
Because rhinos are very nearsighted, they often charge when startled; in the wild, rhinos have been observed charging at boulders or trees. This defense mechanism has given them an undeserved reputation for having a bad temper. Their ears can move independently of each other, and one may be cocked forward while the other is directed backward, or both may perk straight up when an interesting sound that requires total concentration is detected.
The rhinoceros gets its name from its most famous feature: horns. The word rhinoceros comes from the Greek words rhino (nose) and ceros (horn). A rhino’s horn is made of keratin, the same material that makes up our fingernails and hair. Javan rhinos and greater one-horned rhinos have one horn on top of the nose, while Sumatran rhinos, black rhinos, and white rhinos have two.
Horns vary in size, with black rhinos and white rhinos having much longer horns than the other three species. Rhino horns don’t have a bony core like other mammal horns have, and the outside of the horn is rather soft and can be worn down or sharpened after years of use. If a horn breaks off, it can gradually grow back.
The importance of wallowing: All rhinos enjoy a good soak in the mud, but for Asian rhinos, this becomes vitally important to help them get through times of high humidity, when insects can be a problem. Plus, that cool mud feels so good! Rhinos may often share a wallowing spot without any fighting, as if it is neutral ground. White rhinos may create their own shallow mud holes by rolling in watery depressions in the earth.
An unusual relationship: Rhino vision is notoriously poor, but they respond to the alarm calls of other sharper-eyed wildlife, including a bird called the oxpecker. This small bird lives in a mutual arrangement with the African rhinos. The birds hop on a rhino’s back, plucking tasty ticks and other parasites off the rhino’s skin, even entering the ears and nostrils to get those hard-to-reach morsels. The oxpeckers get a full belly, and the rhino gets rid of some irritating bugs. The birds also raise a horrible ruckus whenever they spot trouble for their “friend.”
A group of rhinos is sometimes called a “crash”—an appropriate term for a large and ponderous animal that can crash through just about anything in its way. White rhinos have a hump of muscle on their neck and shoulders to hold up a head that can weigh 800 to 1,000 pounds (362 to 454 kilograms). But while rhinos may look indestructible, their skin is actually quite sensitive, especially to sunburn and biting insects.
HABITAT AND DIET
Meet the rhinos: White rhinos and black rhinos are found in small pockets of eastern and southern Africa, living in grassland and floodplain habitats. Greater one-horned rhinos live in northern India and southern Nepal; and Sumatran and Javan rhinos live in small areas of Malaysia and Indonesia—all three making their homes in swamps and rainforest habitats. All Asian rhinos are excellent swimmers.
African Black rhinos and white rhinos are the same color: they're both brownish gray! How the white rhino came to be called “white” is uncertain. One account says that South Africa's early Boer settlers called it wijde, Dutch for “wide,” which could refer to the wide lip, or the size of a rhino. The wide mouth of the white rhino is perfect for grazing on grasses, while the more narrow, prehensile lip of the black rhino is great for pulling leaves and shrubs into its mouth. Other names used for these two rhino species are “broad-lipped” and "hook-lipped." Guess which name belongs to which rhino!
Black and white rhinos share Africa’s savanna habitats, as they don’t compete for food. Black rhinos can go for up to five days without drinking water, getting needed moisture from succulent plants. White rhinos, the largest of the five rhino species, crop grasses so short when they graze in their habitat that they create “grazing lawns” that benefit smaller herbivores and serve as firebreaks.
The mouth of the greater one-horned rhino looks like a cross between broad-lipped and hook-lipped. Although it is fairly broad, the mouth has a small, prehensile lip. The greater one-horned rhino is both a grazer and a browser, depending upon available food. Many people describe these rhinos as armor-plated, but they are actually covered with a layer of skin that has many folds.
Greater one-horned rhinos, formerly called Indian rhinos, are native to humid, swampy areas of Northeast India and Nepal. The International Rhino Foundation is working to increase this rhino's population in India. It is on its way to reaching a goal of 3,000 rhinos in India and Nepal by the year 2020.
The Javan rhino has a single horn, like the greater one-horned rhino. It is also called the lesser one-horned rhino. Javan rhinos are very rare in the heavily forested areas of Southeast Asia, and they are among the rarest of the rhinos. Conservation scientists have devised an interesting way of counting them. Throughout the rainforest, they have set up cameras with sensors. When a rhino passes the sensor, the camera takes its picture! The conservation scientists can then count them. So little is know about these rhinos, and learning more about these jungle rhinos will help protect them.
Sadly, there are fewer than 50 Javan rhinos in the wild, and none in zoos. The World Wildlife Fund has called the Javan rhino the world’s most endangered large mammal.
The Sumatran rhinoceros is the smallest of the rhinos and is the only rhino covered with a coat of shaggy hair. The Sumatran rhino is considered to be the most primitive, being closely related to the long-extinct wooly rhino. Like the Javan rhino, it is critically endangered, with probably fewer than 80 individuals left in the world. Once found from the Himalayan foothills to Vietnam, it survives today in a few scattered populations in what little forest habitat is left on the island of Sumatra. There has been little success in breeding Sumatran rhinos in zoos.
Dining all day: All rhinos are herbivores, spending the majority of the morning, late afternoon, and nighttime eating grasses or leaves, depending on the species. During the hottest part of the day, they rest. Their horns are used to dig up roots and break branches for better access to food. At the San Diego Zoo and San Diego Zoo Safari Park, the rhinos are fed hay and high-fiber biscuits, along with carrots and apples.
FAMILY LIFE
Rhinos have an interesting social system. The dominant male, or bull, occupies a small, exclusive territory, allowing only one or two subordinate males to share the territory with him. Neighboring dominant bulls show unusual respect for the territory boundaries and rarely trespass except to get water during the dry season. They won’t even follow a receptive female into another bull’s territory. Dominant bulls invest a great deal of time and energy just patrolling their territory, marking it with urine and defecating in dung heaps that serve as a community bulletin board. Subordinate bulls put little effort into such communication with scent, always deferring to the dominant bull when they meet up.
The three Asian rhinos have tusks, and they use these enlarged incisors rather than their stubby horns when fighting or defending their territory. Greater one-horned rhino bulls develop longer tusks than the females. A bull may confront a rival by opening his mouth to show off his tusks. The two African rhinos lack these tusks and so use their horns for defense or fights. Fights among rhinos can sometimes led to death; 50 percent of black rhino bulls and 30 percent of females die from wounds received during a fight. No other mammal has such a high death rate from this type of combat.
Females are not territorial and move through large home ranges that overlap with many other females. Several male territories may lie within a single female’s home range. Adult white rhino females are more social than black rhinos and often stay in small groups of up to a dozen or so that include calves and subadults.
To choose a male, all a female has to do is show up in his territory when she’s ready to mate. The bull approaches the female with a series of “hic-pants,” a breathy inhalation followed by a hiccup. He may rest his chin on her rump to test whether she will tolerate a mating. If successful, a calf is born 15 to 16 months later.
Although wobbly at first, the newborn is soon able to stand on its feet and starts to nurse two to three hours after birth. The calf begins nibbling on solid food at 7 to 10 days of age, although it continues to nurse until it’s 12 to 18 months old; white rhino male calves nurse even longer than female calves, as they will grow much larger as adults. The mother guards her calf carefully from predators such as large cats, hyenas, and crocodiles, as well as from adult male rhinos. Calves and subadults often play, practicing their sparring and head-tossing techniques.
A rhino mother may tend to her calf for up to four years unless she has another baby, in which case she pushes her older calf into independence to make way for the new arrival. The exception is the Sumatran rhino: calves stay with the mother for two to three years, but it may be two years more before she gives birth again.
Rhinos have a variety of vocalizations to get their message across, from a lion-like growl and elephant-like trumpet during a fight to a squeak that can mean “I’m lost” or “Where are you?” Long and short snorts are used for anger, alarm, or when the rhino is startled, and high-pitched screams indicate fear. A “mmwonk” is a deep, resonant sound that signals content.
AT THE ZOO
The San Diego Zoo's first rhinoceros arrived in 1952—a two-year-old black rhino calf from Kenya. Named Sally, she was an immediate hit with zoogoers. However, despite two mates, she failed to breed. Finally, 40 years after Sally’s arrival, a black rhino was born here in 1992. He was named Werikhe in honor of Michael Werikhe, “the rhino man”—a Kenyan conservationist known for his long "rhino walks” to educate people about the plight of the rhino and to raise money to support rhino reserves. He is a good example of what one person can do to make a difference!
Greater one-horned rhinos first came to the Zoo in 1963, and they were among the original wildlife at the San Diego Zoo Safari Park when it opened to the public in 1972. Just three years later, the Park welcomed its first greater one-horned rhino calf and has had breeding success ever since. As of July 2019, a total of 73 greater one-horned rhinos have been born at the Safari Park.
In 1971, 20 southern white rhinos arrived at the Safari Park from South Africa to become the founding generation of the Park’s white rhino herd. Since then, more than 100 southern white rhinos have been born at the Safari Park. Most of these have moved on to live in other facilities around the world.
Today, the San Diego Zoo Safari Park has the largest crash of rhinos and the most successful managed-care breeding program for rhinos anywhere in the world. The Safari Park holds the record for the most rhinos born in a zoo: 187 from 3 species, including 5 generations of black rhinos and 7 generations of greater one-horned rhinos. One of our youngest calves is a fifth-generation greater one-horned rhino, the first such birth in the world!
CONSERVATION
For centuries, the rhino existed largely unchallenged. But the advent of high-powered weapons brought a new and deadly enemy: humans. Over the ages, rhino horn has been used to treat illnesses, especially fevers. Yet like our fingernails and hair, rhino horn is made of keratin and has no healing properties. In Africa, thousands of rhinos were slaughtered each year just for their horn, used for traditional medicines in Asia and dagger handles in the Middle East. By the early 1990s, the population of black rhinos had been reduced by 96 percent and today stands at just over 5,000.
To try to stop the slaughter, African countries began working to protect their rhinos, China no longer approved the use of rhino horn for traditional medicines, and countries in the Middle East promoted dagger handles made of synthetic materials. These efforts reduced rhino poaching measurably. Today, however, that has all changed, and the increasing price paid for rhino horn encourages greedy folks, eager for quick cash and now often affiliated with criminal syndicates, to kill rhinos just for their horns.
Intensive anti-poaching and habitat protection efforts have helped some rhinos make a comeback. Poaching in Indonesia has been almost eliminated, thanks to that country’s Rhino Protection Units. But there is still heavy poaching in South Africa; that country’s average loss is about three rhinos per day. And there are fears that the Javan rhino may soon become extinct, as so few of them can be found.
Fewer than 50 Javan rhinos live in a national park on Java, Indonesia, where they are protected; it is believed that there are no Javan rhinos anywhere else. And there are now just two northern white rhinos Ceratotherium simum cottoni left on Earth—both of them females, and both in the care of the Ol Pejeta Conservancy in Kenya.
Help for rhinos: San Diego Zoo Wildlife Alliance has done a great deal of conservation work with rhinos, especially once our San Diego Zoo Safari Park opened in the 1970s. The Safari Park has the most successful breeding program for rhinoceroses under human care in the world. By July 2019, there had been a total of 184 rhino births at the Safari Park since it opened. That included more than 90 southern white rhinos, more than 65 greater one-horned rhinos, and 13 black rhinos, an important achievement for wildlife that faces severe threats in the wild. Joining partners from around the world that support the International Rhino Foundation, San Diego Zoo Wildlife Alliance is working to save greater one-horned rhinoceroses by translocating them into safe habitat in Manas National Park, Assam. Currently, there are about 3,300 greater one-horned rhinos in native habitat.
All rhinos, whether in Asia or Africa, are in danger of becoming extinct, but we won't give up hope as we continue to closely monitor radio-collared rhinos for years to come. Long-term conservation is our goal, as well as enlisting local community support for rhino recovery. San Diego Zoo Wildlife Alliance supports the International Rhino Foundation by an annual grant and by having the Safari Park’s curator of mammals, Randy Rieches, sit on its board of directors. This support allows us to help fund conservation and rhino protection units in every country that rhinos are found.
Visiting the San Diego Zoo and the Safari Park helps support rhino conservation, too. We can all work together to ensure a future for rhinos.
By supporting San Diego Zoo Wildlife Alliance, you are our ally in saving and protecting wildlife worldwide.
