Rhinoceros

## 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.

## All about rhinos

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.

## What's in a name?

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.

## African rhinos: black and white

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 the animal. 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!

Both species share Africa’s savanna habitats, as they don’t compete for food. White rhinos are the largest of the five rhino species.

## Meet the Asian rhinos

### Greater one-horned rhinoceros

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.

### Javan rhinoceros

Like the greater one-horned rhino, the Javan rhino has a single horn. 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 probably the rarest of the rhino species. Scientists have devised an interesting way of counting them. Throughout the rain forest, they have set up cameras with sensors. When a rhino passes the sensor, the camera takes its picture! The scientists can then count them. So little is know about this rhino species, and learning more about these jungle rhinos in the wild will help protect them from becoming extinct.

Sadly, there are less 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 species.

### Sumatran rhinoceros

This 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 around 200 animals 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 this species 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.

## The importance of wallowing

All rhinos enjoy a good soak in the mud, but for the Asian species, this becomes vitally important to help the animals 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 animals, 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."

## Maintaining a territory

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 rhino species 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 species 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.

## Say what?

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.

## Rhino family life

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.