A Neck Up on the Competition
by Robin Meadows
The giraffe is often referred to as "the animal built
by committee," an assembly of left-over parts, put together
after the divine creator had run dry of ideas.
--Robin Pellew, The Encyclopedia of Mammals
Towering
over all the other animals living on the African savannas,
giraffes look like creatures straight out of mythology. In
fact, ancient Romans didn't quite know what to make of them,
and, thinking they were crosses between camels and leopards,
called them "camelopards." Compared with many other
mammals, giraffes seem ungainly, disproportionate. They owe
their extreme height--up to 18 feet--to the fact that many
parts of their bodies are improbably long. Their legs are
as long as six feet and their necks can extend an astonishing
seven feet. Like most other mammals, giraffes have only seven
neck vertebrae. The difference is that each giraffe vertebra
can be a foot long. Even their tongues are long, with a reach
of up to 20 inches. On top of all that, giraffes walk like
old-fashioned wind-up toys, alternating between swinging both
right legs and then both left legs forward. (Photo by Jessie
Cohen/NZP)
While giraffes (Giraffa camelopardalis) may look like evolution ran amok, they are more than the sum of their parts. Their bodies are superbly adapted to browsing on leaves far above the reach of other herbivores. Rising above the competition gives giraffes virtually unlimited access to tender, nutrient-rich new growth. By stretching their necks, tilting their two-foot heads all the way back, and sticking their tongues out to the furthest extent, the tallest male giraffes can reach leaves more than 20 feet off the ground. The success of this strategy gives giraffes an edge in these days when so many species are endangered. Many ranchers don't mind sharing their grazing areas with giraffes because they don't compete with cattle for forage. Thanks in part to this coexistence, giraffes are generally still plentiful in many areas.
Our modern-day giraffes are one of only two living representatives of a once-varied group of herbivores. The first members of the giraffe family appeared in Africa about 25 million years ago and evolved into a great diversity of species as the world's subtropical woodlands gave way to open savannas. The giraffid family had two main lineages: one characterized by long necks and the other characterized by both short necks and large horns resembling moose antlers. Giraffids lived throughout Africa and southern Eurasia in a swath from Spain to China as recently as two million years ago. However, the diversity and range of giraffids later declined during the ice ages of the Pleistocene due to their dependence on subtropical climes. Today giraffes are found only south of the Sahara, and most live in East African national parks and reserves. The only other surviving giraffid is the okapi (Okapia johnstoni), an elusive short-necked species found in the tropical forests of Zaire.
Giraffes have a great capacity to spark our imaginations, as Newt Gingrich showed when he told his students that men are "biologically driven to hunt giraffes." But for all the enthusiasm that giraffes inspire, their natural history is still mostly a mystery. This dearth of knowledge is due less to a lack of curiosity on the part of biologists than to a lack of financial support. "It's hard to get funding to study them because they're not endangered," says ecologist Tim Ginnett, who recently completed his doctorate on giraffe foraging behavior at the University of California at Davis (UCD) and is now at Texas A&M University studying foraging in deer. "Much of the money goes to elephants, rhinos, and other endangered species."
While few biologists have studied giraffes extensively in the wild, we do have a sketchy knowledge of their behavior. However, what we know raises as many questions as answers. Divided into nine subspecies based on coat pattern and horn number, giraffes form herds like many hooved mammals. But unlike most herding hoofed species, which form tight-knit and stable groups, giraffe herds are unusually informal. The fifteen-odd females and young in a herd may be scattered over a considerable distance and may leave and rejoin at will. "The social structure is fluid and not well understood," says Truman Young, a UCD ecologist who studies how giraffe feeding behavior affects the environment. "What is the relatedness of the individuals? Who stays with whom? What are the advantages of staying in a group?"
Males mature sexually at about four years but keep growing until they reach about eight years. While young males often roam together in loose association, older males tend to be solitary. The older, larger bulls are dominant and devote much of their time to patrolling for females in heat. A dominant bull will approach a herd, draw himself up to his full height and stare at a potential rival. While this is usually enough to make the adversary leave, once in a while a subordinate bull stands his ground and a fight ensues. Giraffes fight by charging and swinging their heads at each other as hard as they can. At up to 25 pounds, their heads are substantial weapons, and the thud of a blow is audible at least 100 yards away. Although violent, these fights normally do not result in injury because the males' nine-inch horns are blunt and covered with skin, and the skin on their necks can be an inch thick. Moreover, their brains are well-protected by skulls that are quite thick and extensively pocketed with sinuses.
When one of the bulls tires of the rapid rain of blows, he flees, leaving the victor free to inspect the cows. Like many animals, including cats and horses, male giraffes can tell a female is in heat by testing her urine. The male nudges a female near her tail to stimulate her to urinate and then takes a sample into his mouth. He then pulls his lips back in a characteristic grimace called flehman and uses his tongue to bring urine droplets to openings in the roof of his mouth. These openings are similar to nostrils and lead to an olfactory membrane called the vomeronasal organ (people lack this organ). Presumably the vomeronasal organ can detect hormones indicating that a female is ready to conceive.
The bull goes from cow to cow and herd to herd, sampling urine until he finds a female in heat. He then separates her from the rest of the herd and follows her around for a day or two, repeatedly testing her urine. Between tests he often entwines his neck around hers and browses by her side. Although she usually thwarts his initial attempts to mount by walking forward, leaving him to slide off her rump, eventually she accepts him. Copulation is brief and the pair returns to browsing immediately afterward.
Fifteen months later, the female gives birth in a traditional calving ground. For reasons yet unknown, females will travel great distances to return to the same site to have their babies. Birth appears to be a rude awakening for calves: Emerging head and forefeet first, they drop six feet to the ground, where they lie temporarily stunned by the impact. They recover quickly, however, and stand within 10 minutes of birth. Initially, a newborn hides in foliage near its browsing mother.
After several weeks, the baby joins the rest of the herd. While its mother has been exceedingly attentive up to this point, now she may stray several miles in search of forage, leaving the baby in a small group of calves called a creche. Another mother sometimes stays to guard the creche but often the calves are left apparently alone. Half of the calves are killed by lions, hyenas, and other predators during their first year of life, and the reason for their mothers' near abandonment remains a mystery.
At about six feet, newborn giraffes are taller than the average person. But even so, their small stature relative to adult giraffes makes them easy prey, and the babies grow fast to make up the difference. Newborns can grow as much as an inch each day and calves roughly double their height during the first year.
At about a year, when they are approximately 12 feet tall, young giraffes no longer remain behind in creches when the rest of the herd leaves to forage. Although the herds are scattered, giraffes don't need to be close together to communicate. Their eyesight is so keen that they can see each other a mile away. Hyper-vigilant, giraffes constantly scan their surroundings for predators and sprint as fast as 35 miles per hour at the slightest hint of danger. "If you're watching them, they're watching you," notes Texas A&M's Ginnett. Members of a herd position themselves so that each looks in a different direction, and they guard each other closely when necessary.
Under most circumstances, healthy adults are protected by their tremendous height and their ability to deliver crushing blows with foot-long hooves. On rare occasions, giraffes--particularly mothers defending their young--have been known to kick lions to death. However, giraffes are vulnerable to attack when they bend over to drink or lie down to sleep.
Drinking is a tricky affair for giraffes because it is the one activity their necks are not long enough for. They simply can't reach the ground! Reaching water entails first bending or splaying their forelegs and then lowering their necks. Righting themselves from this awkward position takes time--a luxury animals don't have when a lion springs from ambush. Water holes are among the most dangerous places on the savanna and at least one giraffe is always on the lookout for predators when the herd lines up for a drink. Zebras, antelope, and other species take advantage of the giraffes' security system and often line up to drink with them.
Fortunately for giraffes, they can go weeks without drinking. But sleeping is another story. Giraffes have to sleep every night, and they are even more vulnerable to attack when lying down than when drinking. This is because standing back up is a lengthy three-step process that involves vigorously swinging their necks backwards and forwards, first to hoist their forelegs to kneeling, then to get on their hindlegs, and finally to get up on their forelegs as well. Giraffes have two strategies to minimize their chances of being attacked while sleeping. As when drinking, at least one member of the herd always stands guard while others sleep. Second, their idea of a good night's sleep wouldn't satisfy even the most manic of us. Giraffes sleep deeply for only five minutes at a time and these naps add up to only about half an hour each day. They do supplement their naps by dozing standing up, but remain alert during these periods, leaving one eye open, and constantly moving their eight-inch ears.
Besides spending a lot of time watching for danger, giraffes spend a lot of time browsing. Like cattle, giraffes are ruminants, eating quickly and barely chewing their food the first time around. They typically browse for several hours after dawn and several more near dusk, reserving the hot middle part of the day for chewing their cud. The up-to-two-ton adults eat as much as 145 pounds of food a day, selecting new leaves, shoots, flowers, sausage-tree fruit, and other nutrient-rich vegetation. Giraffes grasp branches with their long, black, prehensile tongues and strip off the leaves with their comb-like canine teeth, which are broad and divided into several lobes.
While giraffes will eat a variety of shrubs and trees, their favorite food is acacias, up to 60-foot-tall trees that dot the savannas. Acacias are a nearly perfect food for giraffes. The leaves are up to 75 percent water, which may help explain why these animals can go so long without drinking, and contain virtually all the nutrients they need. Only two are in short supply: salt, which giraffes get by licking natural deposits in the ground, and calcium, which they get by chewing bones.
The only drawback to acacias is that they bristle with stout, pin-sharp thorns up to two inches long. While giraffes feed partly on growing shoots that have soft, immature thorns, they also can--and do--eat hard, mature thorns. "The thorns come out in their dung, still very sharp," says UCD's Young. Giraffes are remarkably well-equipped to deal with these thorns. They can close their nostrils completely, their upper lips are protected by a thick barrier of hair, and they produce great quantities of viscous saliva to help the thorns go down more easily. Moreover, their tongues are nimble enough to reach between thorns to snag a leaf.
It turns out that acacias are also well-equipped to deal with giraffes. Young and his colleagues found that when browsed by giraffes, acacias try to protect their delectable leaves by growing longer thorns. One species, Acacia xanthophloea, more than doubles its thorn length in response to browsing. Giraffes typically browse between three and 13 feet from the ground, and in that range A. xanthophloea thorns reached about two inches, long enough to extend past the inch-long leaves. But at 16 feet up, the thorns were shorter than the leaves. Thorns were also shorter than the leaves in A. xanthophloea near the research camp, where giraffes hardly browsed them. This is the first evidence that herbivores can induce plants to increase their thorn length in an attempt to defend their leaves.
Another intriguing aspect of giraffe foraging is that males and females often browse in different parts of the savanna. While males tend to prefer wooded areas, females with babies like wide open spaces. Young and colleague Lynne Isbell found that the optimal feeding height (based on the number of bites per second) is about 60 percent of adult height, perhaps because their heads are freer to move. But females with babies typically browse in areas where the shrubs are too short to eat at the greatest rate. While no one knows for sure why they do this, Young and Isbell speculate that the mothers sacrifice their foraging efficiency for the safety of their offspring--it is easier to spot predators in open areas.
Answering such questions about giraffe behavior is of more than academic interest. "We need to know how they use their environment because it could help in the future," says Texas A&M's Ginnett. "We're looking down the road for when we do need to manage their habitat." Giraffes are already in trouble in west Africa and those in the eastern parts of the continent face an uncertain future. While giraffes have had the good fortune of not having to share their food with other animals, it may soon prove a tall order to live side by side with more people.
Robin Meadows is a contributing editor to ZooGoer.
(ZooGoer 25(4) 1996. Copyright 1996 Robin Meadows. All rights reserved.)
