4

The Ultimate Survivor

It’s amazing how an animal the size of an elephant can simply disappear. Once, I was in Uganda with my guide Boston, and we’d been tracking a breeding herd of twenty or so elephants along the Nile river. They were standing in a clearing about ten yards away, grazing on acacia bushes and stripping the branches bare of their leaves.

The matriarch knew we were there, as she kept raising her trunk in our direction, sniffing the wind. She was calm, though, so long as we kept our distance and tried to stay downwind of the herd. With her was a newborn calf. As the soldiers in Kenya discovered, this can make possibly the most dangerous combination, as a mother will destroy anything, or anyone, that comes near her baby. But in this instance, I felt safe. There was enough cover and Boston reassured me that we were fine, so I followed him as we crept along a trail.

‘Look over there,’ he pointed.

I stared into the thick bush ahead. ‘What?’

He smiled menacingly. ‘Those bushes. In my language we call it the devil’s armpit.’

‘Why?’

He chuckled, ‘Because it’s scraggy and bushy and can hide all sorts of nastiness.’

It was remarkable to see these enormous animals, whose backs reached the top of the bushes, stripping all the leaves clean off them.

Then suddenly there was a noise in the distance behind me. It was the faint call of a lion grumbling a mile away. I turned around and tried to listen for the king of the jungle, but after ten seconds there was nothing, so I turned back around.

Looking up, I stared back at the clearing. Where there had been a whole herd of elephants, now there were none. No noise, no movement, nothing. It was as if they had never existed.

I was astounded, ‘How on earth did that happen?’ In my naivety I suggested that we might follow them out of curiosity.

Boston laughed. ‘No, they are gone, they will hide now, and anyway, we never go into the devil’s armpit, because even if you walked a metre away from one, they would be invisible; then one false move, and you’d be tusked and stamped on. An elephant is 7 tonnes of silence. You’d be food for the lions before anyone even found your trail.’

Elephants are huge, which makes their silence and ability to blend in all the more surprising. Their size has affected every part of their biology, from how much they need to eat and drink and how they keep their temperature regulated, to where they live, what they feed on, and how successful they are at producing calves. It’s all about eating, heating and sex.

It seems obvious that the bigger an animal is, the more energy it needs over the same period of time. This is what we call the metabolic rate. But the metabolic rate doesn’t increase at the same rate as size does: a 6-tonne elephant needs only 400 times the energy of a 2-kilogram rabbit, not, as you might speculate, 3,000 times the energy. Bigger animals are more efficient with their energy than smaller ones, particularly at conserving heat. That’s because, as an animal gets bigger, its volume grows at a faster rate than the surface area of its skin.

The stomach and intestines of a bigger animal also take up a proportionately larger amount of its body. That means food spends more time in their gut, so they are able to extract more energy and nutrition than a smaller animal and still get all the nourishment they need. The upshot is that large animals can eat lower-quality forage than a smaller animal. An elephant needs to eat only 5 per cent of its body weight every twenty-four hours, whereas the smallest antelope species in a similar environment – the dik-dik – needs to eat 20 per cent of its body weight.

They might not be precious eaters, but to meet their enormous nutritional and energetic demands, elephants need to eat a lot, and can be found feeding for around eighteen hours a day given the chance. They eat almost constantly with only short periods of rest, usually in the early hours of the morning and around midday when temperatures are at their highest.

Elephants have evolved into the ultimate herbivore generalists. Whereas most herbivores tend to be either grazers (who eat grass) or browsers (who eat woody plant material), elephants scoff the lot. They can eat everything from fruit, leaves, fresh shoots and flowers, to grass, roots, branches and bark. What they eat depends on what is around, and they switch between browsing and grazing depending on the time of year.

The savannah of sub-Saharan Africa broadly has two seasons: the cooler, dryer winter; and the warmer, wetter summer. The first rains at the beginning of summer lead to a flush of green grass, creating an abundance of food after the comparatively lean, dry winter. During summer, elephants get more than 90 per cent of their dietary requirements from grass, but during winter, when grass availability and quality drop dramatically, they switch to browsing, and target a wide range of woody plants from large savannah trees to small shrubs. They eat bark, dig up roots and tubers, and I’ve been told they have even been seen to munch on the grassy nests made by weaverbirds.

While the bulk of an elephant’s food comes from a few abundant favourites, some elephants have been known to eat more than a hundred different plant species. Being unfussy eaters stands elephants in good stead to find sufficient food to keep themselves going across a diverse range of habitats and in all seasons.

Both males and females need to eat a large amount, but the way they meet their daily calorie requirements is quite different.

Male elephants become independent and move away from their family groups as they hit adolescence, usually around fourteen years old. By this age, males also start to grow much more rapidly than females, who tend to reach their maximum height by the age of twenty, whereas males keep growing throughout their life.

Remember, this larger size means that males have a lower metabolic rate, so need less energy per kilogram of body weight, and can eat even lower-quality, more fibrous food than female elephants. Males feed on taller trees than females, eat parts of the tree that females would turn up their noses at, so to speak, and are much more likely to push a tree over, strip away the bark and gorge on whatever is left.

Not only does their size make the males more powerful and destructive, like in many mammal species (including humans, allegedly), male elephants are more likely to engage in risky and adventurous behaviour. These two make a fiery combination, sometimes witnessed when they come into contact with the human world. It’s usually the males that go off raiding in farmers’ fields, stealing the highly nutritious and no doubt tasty crops planted by people.

Crop raiding allows a male elephant to get a maximum nutritional return for minimum time and energy – possibly getting up to almost half of his nutritional and energetic needs in only 10 per cent of the usual foraging time; a clever move, sometimes worth the risk, especially if he needs that energy to find a mate and reproduce. Of course, the strategy comes with a significant danger of injury or death, as farmers and wildlife managers designate them as rogue and often kill these ‘pest’ animals. But more on that later.

Females, however, tend to be more cautious and stick with their family group. They’re more sociable and spend time interacting with each other. As a result, their mealtimes are frequently interrupted, given that there are more individuals around to create distractions. Motherhood also places extra energy demands on females. For the first nine months of its life, a calf will consume up to 13 litres of milk a day, and a mother’s energy requirements go up drastically. So, females have to find higher-quality foods than males to counteract these issues, and to provide suitable food for calves that are beginning to add solids to their diet.

Consideration of calves is so ingrained in adult females, they are even known to reach for higher food when they are near youngsters. This extra effort means that enough food is benevolently left lower down in the canopy for the juveniles to eat. Calves are small-bodied and growing fast, so they need all the help they can in finding the best quality food. As calves, male and female elephants forage in the same way. It’s only in adolescence, when the males quickly get bigger, and the females prepare for the demands of reproduction, that their feeding behaviour starts to diverge. But while they are young, it makes them highly vulnerable during periods of scarcity such as a drought, and the mortality of young elephants is one of the main natural controls of elephant numbers.

The size of area that an elephant uses to meet its nutritional needs and allows successful reproduction is known as its ‘home range’. Its extent depends entirely on the environment, and the variations can be enormous. In areas with high rainfall and plenty of resources – such as Lake Manyara National Park in Tanzania – their annual ranges can be less than 100 square kilometres. Contrast that with the arid desert environment of Namibia, where home ranges extend to 14,000 square kilometres. However, the all-time record belongs to a female elephant from the Gourma population in Mali that walked across 32,000 square kilometres in a year.

As food becomes scarcer and watering holes dry up with the changing seasons, an elephant’s range changes. They often have larger ranges during the wet summer than in the dry winter, when they have less energy to travel far. Both males and females are likely to be sexually receptive during the wet summer, because there is more food around to support the energetic business of finding mates, going into oestrus and, of course, growing a baby.

Because they are socially independent, particularly when on the hunt for a female, mature adult males have much larger roaming areas than breeding herds and they move much faster. Males commonly go into a heightened sexual energy known as musth in the summer. It’s a period marked by surging testosterone levels that can last for several months, swollen and weeping temporal glands on the side of their head, and the dribbling of urine that has a very strong, distinct odour.

During musth, male elephants can often become aggressive and highly frustrated; their sexual energy overflows and they become desperate to find receptive females. Musth males have one thing on their mind, and they don’t mind who or what they have to fight to get it. Or indeed how far they have to walk to find it – males in Amboseli, Kenya are often recorded walking over thirty kilometres a day repeatedly to find females. And it’s the older males that tend to be the most vigorous, travelling fast over very large areas. All this marching around requires a lot of energy (hence why it’s typically done in the food-rich summer), but it significantly improves a male’s chances of passing on his genes.

In the dry winter season, adult males will shrink down their range and move around far less. They tend to focus on patches of woody vegetation that provide abundant, but low-quality food, and rely on their considerable fat reserves to see them through the leanest time of the year. Females and their family groups have less flexibility, because of the constraints of social living and their need for higher-quality food. So, their ranges have to continue to include a greater variety of feeding areas.

In order to find all this food, elephants need to be excellent navigators, and their spatial memory is rightly celebrated. Food and water sources can be distributed patchily over a huge area, and they might be useful only at a specific time of year. It’s very impressive that elephants can go months, or even years, between visits to a particular location, and need to remember when a food or water source is worth visiting, not simply where it is.

A GPS tracking study in the arid scrub of Etosha National Park in Namibia showed that elephants made very direct and intentional movements towards a specific water hole from up to fifty kilometres away. Not only were the elephants able to navigate directly to these specific locations, but they invariably chose the water hole that was nearest to them, demonstrating the kind of detailed navigation that these days I can only achieve with the aid of electronics.

Finding water is a vital consideration in an elephant’s wanderings and their distribution across the savannah is mostly determined by where it can be found. Fully grown adult males need well over a hundred litres a day, so regular access to water is crucial for an elephant’s survival. They commonly drink at least once a day during the wet summer, and every two or three days during the cool season, when many watering holes dry up. Smaller-bodied calves who tire easily, and mothers nursing their young with milk, both need lots of water every day, so family groups have to stay relatively close to watering holes.

This requirement of family groups to stay close to water can have disastrous consequences. In the early 1970s, Tsavo National Park in Kenya suffered a serious drought. Surface water remained in some areas, like the Galana River system, but two years of low rainfall had seriously reduced the amount of grass and edible tissue on woody plants. The meagre amount of forage near the remaining surface water was quickly eaten and many female elephants, trapped by their instinct to stay close to the water, starved to death. It wasn’t any better for the males either. Those who dared to walk further away to find food became so dehydrated that when they returned to the river and drank desperately, their stressed bodies ended up shutting down completely with this sudden, large intake of water and many perished. By the time the drought lifted, over 6,000 elephants had died.

This may be merely a taste of what is to come. Climate change will have a massive impact on sub-Saharan Africa, with more frequent extreme heatwaves and a major change in rainfall patterns, which will lead to a drier climate in southern Africa and a wetter environment in tropical East Africa. These changes are already being seen, and will have profound implications for wildlife. The available range for elephants will inevitably shrink over the coming decades, as habitats on the edge of the range become uninhabitable. Sadly, as these roaming zones shrink, more and more elephants will die in tragedies like the Tsavo drought.

Aside from feeding, control of its body temperature (known as ‘thermoregulation’) is the other most important factor in determining what an elephant does with its time. The average body temperature of an elephant is very similar to ours, at 36.5°C, and it’s critical for an elephant to maintain that within a fine margin to prevent overheating or getting too cold.

An elephant has less skin surface area proportionately than a smaller herbivore, so they are better at conserving heat. However, in summer the savannah regularly sees temperatures soar over 35°C, making it more important to lose excess heat. This is compounded by those large exposed bodies, which absorb heat directly from the sun and surrounding landscape. To counteract this, elephants have evolved behavioural and physiological tactics to keep cool.

Their main thermoregulation strategy is to get out of the sun during the hottest part of the day. That’s why you’ll see family groups and independent males looking for shaded woodland areas as midday approaches. Under the shade of trees, they can rest and keep cool. If they can find water to bathe in, that cools them down even faster.

Elephants are accomplished swimmers, despite their considerable size and weight, often using their trunks as a natural snorkel. As well as using rivers and lakes to cool off, elephants can easily swim across open expanses of water to escape potential threats, or to reach a safe spot where there is access to food. Even better than swimming, mud wallowing is a really efficient way of cooling down, and elephants in the salt pans of Botswana have been spotted carrying water from one place to another to make sure they can always wallow in their favourite mud holes.

Elephants don’t have sweat glands, but they do lose water through their skin from evaporation. This can account for up to three-quarters of their heat loss, but that water needs to be replaced, hence their need to drink so much, so often. Then, of course, they have those ridiculously big ears – particularly on African elephants – that make up around 20 per cent of their total skin surface area, and play a very important role in preventing overheating. The ears are laced with blood vessels that can carry up to 18 litres of blood a minute, and their size, manoeuvrability, and comparatively thin skin make them a very effective heat-exchanging device. They are, effectively, giant air conditioners.

The flow of blood to the ear can be controlled by the dilation and constriction of the blood vessels, depending on the weather outside. During the hottest part of the day, blood is pumped into the ears. The liquid going in is three degrees warmer than the blood coming back out of the ears, showing how effective they are as a cooling system. When the air temperature is really hot, elephants flap their ears back and forth to make this work even more efficiently. When the weather is cooler or it’s raining, elephants hold their ears flat against the head and constrict the network of blood vessels. This reduces inward blood flow and limits heat loss from the body.

The large ears of the elephant are a remarkable adaptation. They allow elephants to tolerate temperatures in excess of 40°C and enable them to remain active during the hottest part of the year – the peak of the wet season. This is vital if elephants are to get enough food to meet their energy demands. The role of the ears in thermoregulation also gives us a possible explanation for why mammoths, who lived in the cold tundra landscapes of the northern hemisphere, had much smaller ears than their cousins in the savannah. Mammoths had the opposite challenge of maintaining their body temperature by conserving heat at all costs.

Some ongoing research suggests that African elephants may also even use their erect penis – which can be almost two metres long – in the same way as their ears, to cool down on very hot days by getting it out, so to speak, and splashing it with water. Perhaps mammoths had the opposite problem in that department, too.

Given their food, water, and temperature requirements, it is a wonder that elephants can survive in deserts, and yet some do, living right at the limit of what the species can endure. The desert elephants of Mali and Namibia regularly go for days without water, while experiencing daily temperatures that frequently top 40°C. These elephants have evolved some unique behavioural adaptations to survive in such an extreme environment. Within their vast ranges, they seek out small patches of food using their excellent memory. In times of extreme drought and food scarcity, young desert elephants even ingest the dung of adults† to get supplementary nutrition and water. Elephants there have been spotted urinating on mud and splashing this over themselves when wallowing holes are dry, and they can also cool themselves by spraying water stored in the pharyngeal pouch when surface water is not available.‡

As well as influencing their daily rhythms, the sheer size of elephants and the amount that they need to eat has a profound impact on the landscapes they live in. Elephants affect their neighbourhood so much that they are classified as a keystone species. That is, one that has a disproportionate effect on the ecosystem it inhabits. Other examples of keystone species are the wolves of Yellowstone National Park, lions, and sea stars.

As elephants forage, they consume vast amounts of plant material, uproot entire trees and dominate water sources. This incredible ability to change their environment completely and to have an impact on the availability of resources is greater than any other vertebrate, except humans. It’s an impressive sight to watch an elephant uproot a tree, wrapping its trunk around the tree to bend and weaken it, and pushing with its mighty strength – they make it look so effortless.

In areas that have high densities of elephants, their intensive foraging can even lead to the disappearance of their favourite tree species, and as elephants have been confined to ever smaller areas, there has been concern that in some parts of Africa they are damaging and degrading the savannah to an irreversible extent and in doing so, reducing biodiversity.

But elephants do more than simply destroy. The African savannah is a complex ecosystem, defined by two plant forms that are competing for resources: grass and trees. In most environments, only one of these forms dominates: grass in the case of steppe, and trees when it comes to forests and jungles. In the savannah, they coexist in an uneasy balance, with the winner at any one time determined by rainfall, soil nutrients, fire, and which animals are eating them.

Whilst uprooting and eating trees seems destructive, it helps other species in many ways by creating more complex ecosystems: in northern Kenya and north-east Tanzania, frogs and lizards are more abundant in areas that have more elephants feeding. This activity also makes it easier for smaller herbivores to get at food that would otherwise be out of their reach. And the sheer volume that elephants eat helps, too, because it encourages new plant growth, of a higher quality.

By opening up dense thickets, elephants even help lions and leopards, as it allows them to get into areas favoured by small herbivores. But it doesn’t stop there: by digging with their tusks and feet, elephants enlarge existing water holes, and excavate new wells when they access sub-surface water and mineral-rich sediments. The movement of elephants across the savannah has also created defined ‘highways’, which are subsequently used by all sorts of other creatures for many years to come.

Even an elephant’s dung has an impact on the environment. Because their diet is so fibrous, only 50 per cent of the plant material will be digested. Given how long food stays in an elephant’s digestive system, and the ground they can cover in this time, their dung can distribute huge quantities of nutrients and seeds all over the savannah. Digestion helps the seeds that elephants swallow to germinate, whilst the nutrients in the dung provide the seeds with everything they need to get established. So elephants are deemed to be central in maintaining plant diversity and distribution, giving them the nickname, ‘mega-gardeners’.

Whilst elephants do damage areas in which they are overcrowded (often due to fencing-in or human-driven habitat loss), when left to their own natural devices, they cleverly maintain the health and diversity of dynamic savannah, grassland, and forest habitats. Their forestry techniques are part of a finely balanced ecosystem and anything that happens to them has a knock-on effect. Without this keystone species, the entire ecosystem could disappear. The behaviour of the elephant is hugely complex, and we are only starting to understand their pivotal role in the environment and what that means for the other species with whom they share the landscape.

It’s becoming very clear that these giants have a fundamental part to play in nature and much of this is down to their enormous size. But their importance doesn’t stop there. Elephants aren’t simply big eating and breeding machines, they also happen to be highly intelligent, sociable creatures that rely on love, relationships, and interaction far more than we might think.

† A practice called coprophagy.

‡ The pharyngeal pouch is a pocket of tissue located at the top of the digestive tract, and this behaviour has only been seen in other elephants as an emergency cooling technique after a stressful encounter that might cause them to overheat, such as fleeing from danger. Desert elephants are the only ones that use the pharyngeal pouch to cope with ambient high temperatures and a lack of available surface water.