The Savannah Challenge: Herbivores and Carnivores

The East African savannah is one of the richest biotopes in the world. It's home to some 2 million large herbivores. In season, these mammals feed on the abundant vegetation. Life seems easy, yet they're constantly facing danger from predators. Carnivores form the apex of the food chain. However fierce, however dominant they may seem, they are virtually dependent on the existence of their prey. So they too are vulnerable. Which group is better adapted to the challenge of survival in the savannah? The carnivores? Or the herbivores? The predators? Or the prey? Dawn breaks, and the first light rekindles the daily cycle of life. Photosynthesis can now resume. Plants can grow, providing food for the herbivores. Now is when many diurnal species emerge from the topar of the night, and begin to graze before the sun evaporates the dew. After the cold and the darkness, sunrise on the savannah seems to celebrate the miracle of life. And the morning is usually when female topis give birth. This female topi is preparing to give birth to a single calf after a gestation of 8 months. Immediately after birth, this little topi is capable of seeing the world surrounding him. This is when mother and newborn calf are vulnerable to predators. There's no time to waste. As the mother removes the placenta, the newborn's instinct is to stand up. So far, so good. Shivering in the cold air, he'd like to suckle, sheltered by his mother's body. But she deliberately steps away. First he must be able to run, to run from danger. Speed, running speed is all he can count on to survive. So he tries, and falls. But that doesn't matter because he's learning to run. And so only 15 minutes after being born, and before feeding, this little herbivore is already capable of galloping across the savannah. Things are totally different for young carnivores. A lioness has come to this canyon to be alone, away from the other adults. She's followed by two other cubs from the same pride, but with different mothers. This is where she's hidden her three cubs, born just a month ago. They weighed a little more than a kilo at birth, and their eyes were closed. They're older now, but still don't dare hazard away from their shelter. These future super predators seem much less independent than the young antelopes. They learn much more slowly about the world around them, but they too must become aware of danger. Until they're two months old, a male lion from the same pride could kill any cub he didn't father. That's why the lioness gave birth in a hiding place. She'll return to her pride two months later, when her cubs are strong enough to join the group. In the meantime, she protects her offspring, and this causes considerable curiosity among the other cubs. For the time being, both feed on their mother's milk, sharing her four teats. When they join the pride at the age of two months, every lioness will be willing to nurse them. This lioness has two cubs. They're seven weeks old. She often moves them to new hiding places to keep them from being spotted by predators. For long journeys or tricky terrain, she still has to carry them in her mouth one at a time. With their long legs, young antelopes don't need so much attention. Higher up the hill, the little topi born this morning needs sustenance. His mother guides him to his first taste of milk. Large herbivores usually give birth to a single newborn. This zebra colt doesn't have to contend with siblings to feed. Things are different for carnivores, as seen in this clan of spotted hyenas. Litters are large, and births do not follow a seasonal pattern, so cubs of different ages live and play together. Younger ones learn to defend themselves against older and sometimes aggressive cousins. They also learn to preserve their position in keeping with their mother's social status. From their first days onward, hyenas have to be aggressive, in particular to suckle from their mother. Hyena cubs are born with teeth, but only feed on their mother's milk for the first year. Cubs that succeed in suckling longer will grow faster, while the others grow weak and may even die. Social life is highly competitive, and there is little time to rest. Lion cubs on the other hand, once they're old enough to join the group, are raised jointly by all the lionesses in the pride, with different generations living together in peace. Even before they are weaned, the lion cubs are aching to join their elders, who enthusiastically devour their prey. The hunting instinct is innate in all carnivores, and even if the cubs are still suckling from their mother, they're already interested in their future prey. This wildebeest seems quite vulnerable, isolated in the middle of the river. This lioness has already eaten, but she's still a threat. The wildebeest isn't going to turn its back to flee. That would be too dangerous. This gives the lion cubs an opportunity to go hunting. The wildebeest has no choice but to defend itself. The wildebeest is cornered. The lioness could easily finish it off, but they simply stand by and watch to see how the younger generation fares. The cubs are still too small to hunt this large prey, especially when the wildebeest fights so well. A lioness steps in and puts an end to the exercise. Facing each other for millions of years, carnivores and herbivores have developed a reciprocal relationship. Predators have eliminated the most vulnerable species, and only the survivors have been able to transmit their genes. At the same time, as prey became harder to catch, only the best hunters were able to reproduce. From one generation to the next, this is the process of adaptation by natural selection between predators and their prey. As soon as young herbivores are weaned, they can graze as much as they want. Carnivores like these little black-backed jackals are dependent on their predators for much longer. They might try insects and other small prey or fruit, but that's not enough. Better to wait for the parents' return. Hope that nothing happens to them, because without their parents, the entire litter would be doomed. The mother jackal has decided to attack a thompson's gazelle. Normally an impressive prey, but this gazelle is injured, and the jackal is ready to run it down until it can no longer defend itself. The other gazelles remain aloof. Living in a herd allows a statistical safety in numbers, but that's no protection for any individual member. The jackal pups wait near their burrow, which began as a termite mound. Their mother can't take them to the gazelle. That would be too dangerous, and the body is too heavy to drag back to the burrow. So she swallows the meat and carries it in her stomach, which prevents it from being stolen on the way home. Then she can regurgitate it for the pups. The father was also away hunting and brings more food for the family. Jackal couples mate for life and cooperate in taking care of their large families. Leopards lead a solitary existence. This female is on her way to care for her single cub for 12 to 15 months. Whenever she sets about inspecting her territory or goes hunting, she leaves the cub hidden in the bushes. Leopards are slower than cheetahs. They prefer to lie in ambush in the brush so they can better surprise their prey. This rabbit is intended for the leopard cub. It might look huge compared to the size of the cub, but carnivores can only eat what they kill, and nothing must go to waste. Still, carnivores require less food than grazing animals in terms of weight or volume because animal flesh is richer in protein and calories than grasses and leaves. When the youngster has eaten his full, the mother can finish off the rabbit's carcass. Since carnivores spend less time feeding than herbivores, they have more time to rest. Or for young carnivores, more time to work off their energy. All these physical exercises will make this young leopard a better hunter. Lions also rest for nearly 18 hours a day. Cubs have many brothers and sisters and plenty of time for play fighting. This will come in handy for hunting, and one of the cubs could one day become leader of his pride. The third big cat of the savanna, the cheetah, is a solitary non-territorial species. Unlike leopards, female cheetahs have litters of three to six cubs. Feeding and protecting them requires constant care. Young cheetahs are often attacked by other predators, especially hyenas. Typically, less than half of a cheetah litter will survive to adulthood. Cheetah cubs are either napping or in perpetual motion. Playing together builds strong muscles and teaches them to control their body. Their predator instinct drives them to test their powers against a common eland. The antelope weighs nearly 100 times more than they do, but that doesn't discourage the cheetah cubs. These cats demand affection. Cuddles play an essential role in social bonding. Young herbivores, like these waterbugs, also need to work off their energy, and that includes fighting. Jousting by young males prepares them for later, when they will attempt to win a harem. The older they are, the more serious and violent these clashes can become. Young animals can play, and not only in the savanna. Much higher, at 2,000 meters altitude, the Virunga Mountains are covered with a rainforest. This impenetrable jungle is one of the last refuges of the mountain gorilla. The dominant male watches over his family, composed of several females and their young, plus one or two younger non-dominant males. While adults are calm and even-tempered, young gorillas are bundles of energy, whether alone or playing with others, climbing and jumping in the branches. For these generally peaceful herbivores, playing means learning to move through the forest, above the ground, in order to reach the leaves, the stems, and the bark they feed on. Sometimes the brouhaha and the excitement will annoy an older gorilla, but that's not really a problem. And it's even better when an adult male's silvery back is used as a trampoline. Gorillas are not territorial creatures. They don't stay very long in the same place. They move easily through steep terrain and dense vegetation, so they can enjoy a varied diet. Gorillas spend a third of their time eating, with a break in the middle of the day. Adults will not only eat 30 kilograms of plants and fruits every day, they will sometimes chew on rotting wood for insects, which are rich in protein. To digest the food required to fuel 200 kilograms of muscle, gorillas have proportionally longer intestines than humans. This explains why their bellies are so large. A few kilometers from there, at a lower altitude, we encounter another species of primates. Chimpanzees are lighter and smaller than gorillas, and they can swing through the branches to the very tips to pluck fruits and tender leaves. Young chimps are easily recognized by their pink faces. They are quick to learn which plants are edible, and they have excellent memories. Older chimps can be less acrobatic in search of food. This one climbed a jackfruit tree, which produces its heavy fruits. They can weigh five kilograms directly on the trunk. His powerful canine teeth crack open the shell to uncover its dense, delicious flesh. Chimpanzees will generally let their others know when the fruit on a tree has ripened. They may also join up to hunt small monkeys and to steal bird's eggs. They divide their high-protein food according to their hierarchical position in the troop, but fresh meat generally accounts for only five percent of their diet. Each troop seems to have its own food culture. Some meat plant species that chimps from other troops won't even try. This is evidence that individuals learn to identify edible foods more through transmission from one generation to the next than through personal experimentation. Chimpanzees travel a great deal around the territory of their troop. They know where every fruit tree is located and how to get there. The alpha male, the leader of the troop, often patrols the perimeter of the troop's territory to protect against intruders. If chimps from a neighboring group try to enter, the conflict soon turns violent and can result in multiple deaths. During his inspection tour, the alpha male also checks fruits and other edible plants for ripeness. Figs are especially prized. Food resources must be protected from neighboring groups, a problem that seldom arises among grazers, even in territorial species, which typically face less competition for food than carnivores do. The savanna is dotted with large fruit trees, a valuable source of food for olive baboons. These highly social creatures live in troops of about 30 individuals, and they're far from being strict vegetarian. Plants form the mainstay of their diet, but they also catch insects, steal birds' eggs, and hunt small mammals. Females give birth to a single baby a year. At about eight weeks old, the baby can reach out to the most readily available food, but without separating from its mother. This provides both mother's milk and a very pleasant way for baby to travel. Baboons are opportunistic feeders, so they're not dependent on a single type of food. They can live in a broader range of habitats than gorillas or chimpanzees. They face little or no stress for food, and have developed one of the most complex social and hierarchical systems in the animal kingdom. Nearer to the lakes and rivers, the savanna becomes lush and green. Herds gather at watering places to quench their thirst, especially the largest terrestrial animal, the elephant. This pachyderm needs close to 200 liters of water a day. Elephants also wade into the water to feed on reeds and rushes, plants that are particularly rich in the fiber they need. Like many herbivores, elephants like variety in their diet. They move from plant to plant. If only a few steps away, this preserves the shrubs for another day without killing their food source. That's something carnivores cannot do. When elephants uproot grasses or break branches, they give them a vigorous shake to remove dust, insects, and dead leaves. If an elephant loses its trunk, as sometimes happens after an attack by lions, it can no longer feed itself. The shape of their heads and the location of their teeth prevent them from grazing directly on the ground. There are 10,000 muscles in an elephant's trunk. It takes time for young elephants to learn to master them, but for the first three months, their only food is mother's milk. Then they copy grown-ups and learn to pluck grass in a circular motion. Still, they need calcium and fats and continue to suckle for the first two years of life. Elephants hardly sleep and spend up to 16 hours a day feeding. It takes time to eat 150 kilograms of plants each day, especially because they're finicky and always choose the best leaves, the highest they can reach. Giraffes can feed on leaves five meters above the ground, on branches that an antelope cannot reach. This limits competition for food between herbivore species, especially in the most arid areas. Giraffes choose the most nutritious foliage as they forage from tree to tree. Giraffes spend much of the day feeding and need about 30 kilograms of plants a day. The rest of the time they rest and ruminate. Rumination is a digestive process specific to certain herbivores in which they chew their cud. In other words, they bring food from the stomach back into the mouth to chew it again. Having several stomach pouches allows for fermentation and absorption of nutrients. This improves the energy yield from relatively nutrient-poor plants. The Bovidae family has many ruminants, including elans, buffaloes, and all the antelope species. They swallow their food quickly and chew it later, when they are less vulnerable. They can survey their environment and protect themselves from predator attacks. Herbivores depend on their keen senses to spot a threat. Their large ears can turn in different directions to locate where sounds are coming from. Their eyes are set on the sides of the head, which gives them a very wide field of vision. Wild cats, on the other hand, have frontal-placed eyes for three-dimensional vision that allows them to better evaluate distances. By living in a herd, Thompson's gazelles increase their probability of spotting a predator, and once they do so, they never take their eyes off, showing their attention by facing it squarely. The cheetah, aware that it can no longer attack by surprise, simply gives up the chase for now. He cannot afford to waste his energy on a hunt that is doomed to failure. Carnivores rely on their physical condition and their instincts to hunt. They have to weigh the balance between the caloric value of their prey versus the energy expended in hunting it. This is what biologists call optimal foraging theory. A predator will be successful only if it knows the capabilities of its prey. Is feeding any easier for the herbivores? During East Africa's two wet seasons, there's plenty of green grass for the antelope. These cobs need only to bend down to graze on the fresh, sappy grasses. But things become more difficult in the dry season. Grass grows pale and dry, no longer providing sufficient nutrients. Food is scarce for species that graze only on grasses. Fortunately, the herbivores can sense that beyond the horizon, the rains have begun to fall and the savanna is turning green again. So the herds assemble for an extraordinary journey. This is the annual great migration, the most spectacular symbol of African wildlife. Nearly a million and a half wildebeest and zebra begin their weeks-long journey, forming gigantic columns, climbing the hills and crossing the great plains. It is a perilous journey of 400 kilometers, with dangers at every stage. Nearly 10% of the wildebeest will die somewhere along the way. Great rivers to cross, the danger of drowning, Nile crocodiles form meters long and weighing half a ton, lurking in ambush. Before facing the danger, the wildebeest come to a halt. They could spend days here, crowding on the riverbank, until one wildebeest, possibly bolder or hungrier than the rest, finally takes the plunge. The rest of the herd follows, sharing the risk of falling to the The weakest are caught in the crocodile's jaws, pulled under and drowned. Carnivores feed on herbivores. That's nature's implacable law. It's not a question of fair or unfair. With luck, the vast majority of the herd could cross the river unharmed. But a few dozen kilometers ahead, there's yet another river, and a new set of dangers. This bloodbath naturally attracts other predators, and not only scavengers looking for easy prey. This lion, who seldom hunts on his own, considers it well worth taking the wildebeest carcass from a lethargic crocodile. Predator species that live in family groups, like lions in their prides, or hyenas in their clans, usually share the spoils of their hunt. This morning, however, the dominant male won't let one of his females eat just yet, and her submissiveness won't change a thing. All she can do is wait. But why? Did she spurn his courtship? This shows how the dominant member in a carnivore species can control access to food. Herbivores don't have that problem. When they're too hungry to wait for nightfall, a lioness will hunt by day. The lioness goes directly to the throat, killing the wildebeest by suffocation. In his misfortune, at least he was fortunate enough to fall to a predator who can kill him in an instant. The lioness still has to drag the 150 kilogram carcass from the canyon. It's a huge effort, but well worth it, because she now has enough to feed the entire family. The dominant male isn't hungry, so he lets the rest of the pride feed on the wildebeest. The taste of flesh proves irresistible, and everyone fights for the best pieces. The family ties that bind the members of the pride keep things from getting out of hand. The lion finally decides to join the feast. There is no opposition to his arrival. Another male in the same pride approaches, but the alpha male shows his displeasure. The hierarchy is preserved between males. This means the other male can eat too, but only when the leader has finished. Carnivores sharing food reinforces social bonds, so even solitary predators like cheetahs sometimes choose to live together. This usually occurs among males, brothers from the same litter. This confers a definite advantage in hunting. Yes, they will have to share their prey, but that's not a problem, because they only attack larger animals, like gazelles or young antelopes. These four brothers have spotted a wildebeest herd. They split up, two of them to the front of the herd to draw their attention, one to the back of the herd, and the fourth to run down the most vulnerable wildebeest. In the short grass, cheetahs cannot hide and ambush. They rely on their running speed to catch their prey. They've caught a wildebeest, but the cheetahs won't have time to finish off their prey. The hyenas watch the hunt and know the cheetahs won't put up a defense. The slightest injury could prevent the cats from running at top speed, and therefore prevent them from hunting. The hyenas can feast on fresh meat, but the cheetahs will have to rest for hours before they can resume the hunt. Predators tend to devour their prey in a hurry. They're never sure they can hold on to it for long. Despite the hierarchy within the hyena clan, individuals fight for access to the food. They also have to chase away hyenas from other clans as they devour everything they can, until the arrival of a lion signals that the feast is over. There aren't enough hyenas to defy the big cat. Otherwise, they could have fought him off until he was discouraged or even fatally wounded. But not today. This lion can eat in peace. Not all carnivores depend only on hunting to survive. Hyenas often make do with carrion, as do jackals, but they have to keep the spoils from others. Unfortunately, something has changed in recent years. As lion populations have fallen, the carrion available daily has decreased, and to avoid depending only on what lions kill, hyenas are hunting more. And because they are better fed, their population has increased. In some places, the overpopulation of hyenas is a threat to other predators in their fierce competition for food. Hyenas will attack any animal in a weak condition, like this wildebeest that sought safety in a river. He is wounded, and the scent of blood proves irresistible. But he hopes to escape by staying in the water. The predators attack, and the end is never in doubt. The wildebeest is disemboweled and eaten alive. Hyenas never acquired the habit of killing their prey first. The balance of nature requires that herbivores outnumber carnivores. In some antelope species, such as the cob, females are overrepresented. This allows the most dominant males to assemble a large harem and produce large numbers of offspring. Things can be tricky. Even in heat, the female may be unwilling to mate. Males need to be patient. Among carnivores, not even the lion can dictate his will. The lioness demands to be courted. The dominant male in the pride can do nothing until the female agrees. In some rare cases, it's the female who does the courting. Things go faster. The male leopard will never keep her waiting. When big cats mate, it often ends aggressively. Mating occurs at intervals of 20 minutes or so, for a day or two. This pattern is necessary to trigger ovulation in the female. The sun sets over the savanna, over the herbivores and the carnivores that have confronted each other all day long, and will do the same tonight and tomorrow and as time goes on. Nature's balance depends on this constant confrontation. Survival is not only a matter of strength, but of successful adaptation. This topi is thoroughly aware of the distance that keeps him safe from cheetahs. He can defy them with his presence, and in doing so, the antelope dominates the situation. All told, herbivores may be less vulnerable than it seems. There may be safety in numbers. Although they live under constant threat, the fittest among them learn survival from an early age. Carnivores, on the other hand, may look tough, but their existence is far from easy. Their natural territories are continually shrinking under pressure from humans. Can we still consider the lion the lord of the savanna, when half the lion population has disappeared in the last 25 years? How can these big cats preserve their freedom and their dignity in reality, and not just in the popular imagination? This young generation of lion cubs doesn't seem to have a care in the world, yet it is on their future that the natural balance of Africa's large wildlife depends.