Monday 13 August 2018

Kalahari Trackers vs. Aircraft – The Ultimate Wildlife Counting Challenge

A team of Kalahari trackers (© Julia Burger), and an aerial survey team (© Christiaan Winterbach).

It doesn’t seem like a fair match. A couple of illiterate guys sitting on the front of a vehicle as it churns its way through Kalahari sand vs. a qualified team of experienced wildlife counters flying overhead in a fixed-wing aircraft. Whilst the first team spend hours staring fixedly at the ground whilst bumping along sandy tracks, the other team count animals directly just by looking out the window from their aerial vantage point. The challenge: who can count wildlife with the greatest precision and efficiency?

This challenge sounds a little like the incredibly uneven match-up between Russia and Spain in the recent Soccer World Cup – whoever bet on Russia taking that one? Yet one conservation researcher was crazy enough to both create the challenge between Kalahari trackers and aerial survey observers, and bet on the trackers winning the contest. Derek Keeping has good reason for his faith in the tracking team, because he knows their secret weapon. Although the guys balancing on the front of his vehicle may be illiterate when it comes to lines of ink on paper, they are among the best in world when it comes to reading animal tracks in the sand.

Let me digress. Why is the challenge of counting wildlife in the Kalahari important in the first place? The location for this particular challenge is not even inside a National Park or Game Reserve. Instead, it is a Wildlife Management Area outside the northern border of the Kgalagadi Transfrontier Park, and people still live there in a small village called Zutshwa. Whilst this area might not seem all that important to those driving through to get to one of Botswana’s renowned protected areas, conservation researchers acquainted with the region know that it is part of the Kalahari Schwelle – a critical part of the overall ecosystem (as mentioned in a previous post).

Map of the Kalahari Scwhelle and the study area chosen for the wildlife counting challenge. Situated between the Central Kalahari Game Reserve and the Kgalagadi Transfrontier Park, this region is a critical part of the Kalahari ecosystem. Map provided by Derek Keeping.

Knowing how many animals live in an area is a crucial first step in conservation, especially if some of the resident species are endangered or threatened by manmade causes. Underestimating the number and diversity of animals living in non-protected areas could lead to land-use planners deciding that an area currently designated for wildlife-related uses (including tourism) could be used for livestock instead. The scene of our wildlife-counting challenge is a Wildlife Management Area that is the traditional territory of families now settled in Zutshwa. Until recently, jobs, meat and cash for the community were generated from this Area by allowing guests to hunt some animals.

Since the nationwide ban on hunting in all forms (subsistence and commercial) on government land, the Zutshwa community have encountered some hard times. Besides no longer being able to hunt for their own meat, those who were employed as trackers in hunting safari operations are now out of a job. It is against this background that Keeping set about finding ways to employ trackers that would benefit both them and the wildlife they live with.

As Keeping points out, “Most people in Zutshwa, and other Kalahari settlements in the region, are now destitute. Being so close to the past as they are, they have remarkably positive attitudes towards wildlife and conservation compared with most rural areas of Botswana, and many of them want jobs in wildlife and tourism rather than ranching and agriculture. Unfortunately, current development policies in these remote areas favour a future of livestock husbandry.”

Wildlife counting in Botswana has relied on aerial surveys for over three decades, and the method has become the standard way to estimate wildlife numbers and trends over time. However, the cost of an aerial survey is substantial, leading the government to reduce the frequency of these surveys and focus on the northern parts of the country, where wildlife are more abundant.

Wildebeest and zebra being counted from the air. Is this the best method for monitoring wildlife populations long-term? © Christiaan Winterbach.

When asked why he thought that using trackers to count animal tracks on the ground would be preferable to observers counting animals from airplanes, Keeping explains: “There is a vast discrepancy between the numbers of observations accumulated by observers in an airplane compared to trackers on the ground. Aerial observers fatigue quickly bumping along at 170 kph in an uncomfortable airplane seat, especially when there’s not much to see in a monotonous semi-arid savanna landscape with naturally low numbers of large wildlife. By contrast, the sheer numbers of tracks that appear after a single night of animal movement in the Kalahari is astonishing. It was this observation that convinced me that an apples-to-apples comparison of aerial counts and track counts was a worthwhile pursuit.” 

From his seat at the front of the vehicle, the tracker scans the ground for spoor. All the information is then relayed to a recorder in the vehicle. © Julia Burger 2018.

The notion of using an ancient skill to conduct modern research is a romantic one, but will it produce the same quality of information as more sophisticated, expensive methods? If using trackers to count animals is merely a quaint idea that doesn’t produce reliable results, then one cannot justify such a method. So Keeping set up the ecological research version of a penalty shoot out, if you will. 

The tracking vs. aerial survey challenge was set up during the late dry season (Oct-Nov) in 2015. Both teams traversed the 6,425 sq. km area using the same straight line routes across it, covering a total of 648 km. To ensure that one method of counting animals was not influencing the other (e.g. animals being scared off by the airplane and/or the vehicle), they avoided counting the same route twice in one day wherever possible.

In the track survey, the trackers counted the tracks of anything larger than a steenbok for herbivores, and all the large carnivores (i.e. hyenas, big cats, and wild dogs). Ironically, the tracking team was actually given a handicap for this contest by limiting the tracks they recorded to the bigger animals. Trackers can easily count the tracks of animals as small as pangolins, mongoose, and African wildcat, but the aerial survey team would have no chance of seeing these species. Although good trackers can differentiate the tracks of individual animals, the statistical method used in this study simply requires them to count an animal track every time it crosses the road they are driving on.

Lions and other carnivores are almost impossible to count from the air, as illustrated by this one relaxing under a bush during the heat of the day (© Julia Burger 2018). Their tracks, however, are easily counted during a tracking survey (© Gail Potgieter).

To judge the ‘winner’ of the wildlife counting contest, Keeping and his research colleagues used a few criteria: 1) the precision of the population estimates calculated from each method; 2) the ability of each method to determine where the animals occur in the area (i.e. their distribution); and 3) the efficiency of each method in terms of the time and money spent to collect enough data for accurate population assessments.

For the population estimate test, counting by air or tracking by vehicle produced very similar results for six large grazing herbivores – gemsbok, hartebeest, wildebeest, eland, springbok and ostrich. However, the tracking team estimated more kudu than the aerial survey team. Aerial surveys in other areas of Africa consistently under-count kudu, because these browsers spend most of their time bushy habitat, which makes seeing them during aerial surveys rather difficult. Finally, only the tracking team could count enough large carnivores to make population estimates. Carnivores are rarely counted during flights, as most of them are sleeping off the night’s activities under bushes or in dens when the aerial survey team is flying overhead. The beauty of using tracks is that the sand records nocturnal animals’ activities, which are easily read by trackers the next morning.

The second test – determining animal distribution – was convincingly won by the tracking team. Where the aerial surveys showed patchy animal distributions for several herbivore species in the survey areas, the tracking survey revealed more uniform distributions. The latter result makes more sense ecologically, as animals are unlikely to occur only in certain blocks of land, when the whole area provides good habitat for them. The tracking team thus provided a more accurate picture of animal distribution for this Wildlife Management Area than the aerial survey team.

A herd of eland and a lone gemsbok are among the diverse animal species that inhabit the Kalahari Schwelle. © Julia Burger 2018.

The final test, relating to time and money, showed that whilst aerial surveys take less time (1.5 days compared to 15 days of effort for multiple tracking teams), they are more expensive. The aerial survey cost US$ 7,793.79 in total (or $12.02 per km), whereas the tracking survey cost only US$ 4,652.17 ($7.17 per km).

Keeping points out: “Vehicles are by far the most expensive component of the ground track survey, but most Kalahari trackers are also expert horsemen, and with a little logistical creativity I see no practical reason why motor vehicles would be necessary for future track surveys. Even better than horses would be camels; these desert-adapted animals have an advantage over horses, as they need less water and food, and are less likely to be attacked by lions.”

If the trackers did this survey on horses or camels, without vehicles or drivers, then the cost of the survey would be further reduced to US$ 1,399.54, or $2.16 per km. Animal-back surveys have the additional benefit of reducing the pace of the survey, allowing the trackers to record smaller, yet extremely important, species such as pangolins and black-footed cats. Pangolins are threatened by wildlife trafficking, whilst the black-footed cat is endemic to the Kalahari region, yet receives little scientific attention.

If this wildlife counting challenge were a soccer match, the score line would read 3-1 to the tracking team! Although the aerial survey produced reasonable population estimates for large, grazing herbivores (their solitary ‘goal’), the tracking survey did that and much more, at a lower cost. But the benefits of using trackers to conduct wildlife surveys do not end there. This task could be funded, and even generate income for the community, by inviting tourists to join the trackers on wildlife monitoring animal-back safaris.

This would be a unique tourism offering for wildlife-loving, adventure-seeking safari goers, whilst simultaneously helping local people realise the benefits of their own traditional tracking culture and their wildlife. With a bit of technical support from Keeping, the data collected from these surveys will be used to inform population estimates and distribution data, which can be used to highlight the importance of this part of the Kalahari ecosystem. At first it could compliment, but may eventually even replace, the increasingly cost-prohibitive aerial surveys, especially if track surveys are funded through community tourism rather than limited government budgets.

Trackers discuss some of the signs they can read in the bush.  © Julia Burger 2018.

According to Keeping, “Facilitating a new track-based wildlife monitoring programme throughout Botswana’s Kalahari that is led by expert citizen trackers would firstly yield volumes of new data and insights far in excess of what is currently attainable through the aerial survey, secondly create numerous meaningful and well-paying jobs in one of the country’s most poverty-stricken regions, and thirdly be an incentive to keep exceptional track interpretation skills – our shared intangible cultural heritage – alive in the future. Two of these three outcomes are top goals on Botswana’s national agenda, and all would enhance conservation in the long-term. I can hardly think of another single intervention that would check so many priority boxes, and do so much good.”

This tantalising idea could be a triple-win scenario, combining an authentic and unique eco- and cultural tourism experience, local sustainable development in a way that maintains traditional skillsets, and long-term wildlife monitoring and conservation. For a conservationist, the result of this wildlife counting ‘competition’ is more exciting than the Soccer World Cup!

By Gail C. Potgieter

If you are interested in making this idea a reality, please write to Derek Keeping ( and consider a donation to the Comanis Foundation, which is a sister organisation to Tanate Wilderness that works with the community of Zutshwa to develop viable ecotourism within their Wildlife Management Area. Together they are committed to moving the vision of track-based wildlife monitoring forward in collaboration with Botswana's Department of Wildlife and National Parks, first initiating a pilot program in Zutshwa which can then be propagated to other remote communities throughout the Kalahari Schwelle.

Keeping et al. (2018). Can trackers count free-ranging wildlife as effectively and efficiently as conventional aerial survey and distance sampling? Implications for citizen science in the Kalahari, Botswana. Biological Conservation 223:156-169.

Monday 4 June 2018

The Precarious Life of Blue Wildebeest in the Kalahari

Blue wildebeest in the Kalahari © Moses Selebatso

For blue wildebeest in the Kalahari, life is tough. As a water-dependent grazer, survival is all about finding enough grass and access to water during drier years, whilst avoiding predation. Before the 1970’s, this species of antelope survived in the harsh semi-desert Kalahari environs by doing what wildebeest do best – migrating to find water and greener pastures. Today, migration to permanent water sources north of the Kalahari is no longer possible, and wildebeest have had to adapt quickly to modern conditions to survive.

Despite the impressive size of protected areas in Botswana, wildebeest in the Central Kalahari Game Reserve (CKGR) today are all but cut-off from their historical migratory routes. Extensive fences meant to reduce disease transmission from wildlife to livestock, and to control livestock movement were erected since the late 50's, with dire consequences for wildebeest. The wildebeest population in the Kalahari ecosystem (extending West and South of the CKGR, see map) crashed from over 250,000 in the late 70’s to just over 20,000 in 2015 (figures from reports for and by the government of Botswana in 1980 and 2015, respectively). Conserving the remaining Kalahari wildebeest, and allowing their numbers to recover, requires in-depth understanding of their current situation.

The greater Kalahari ecosystem includes the Central Kalahari and Khutse Game Reserves (CKGR and KGR), the Kgalagadi Transfrontier Park (KTP), and the wildlife management areas (WMAs) between them. The area known as the Schwelle (shown in cross-hatchings) covers several WMAs and is a critical resource for Kalahari Wildebeest. © Moses Selebatso

To develop this understanding, Kalahari Research and Conservation conducted an in-depth wildebeest research project in the Central Kalahari Game Reserve. Dr. Moses Selebatso, the project leader, tracked wildebeest movement in the CKGR using satellite collars on females from several different herds. The movement patterns were examined in conjunction with grassland studies to find out more about where these survivors go and what they eat. This work produced three scientific journal articles, and practical recommendations for conserving Botswana’s remaining wildebeest, both in the CKGR and throughout the greater Kalahari ecosystem.

Dr. Selebatso and his colleagues discovered that most of the wildebeest in the CKGR now stay around artificially pumped waterholes, ‘hanging tough’ during the long dry season as the grass around them slowly disappears. The permanent waterholes were created in 1984, in response to the mass die-off of wildebeest and other water-dependent animals due to the then newly erected fences. As the CKGR has no natural water sources that last throughout the dry season, the artificially pumped pans are a lifeline for wildebeest. However, his studies found that this human intervention can be a double-edged sword for wildebeest.

Dr. Selebatso (standing) and a research assistant track the collared wildebeest using radio telemetry equipment. © Niti B. Mishra

Waterholes in the CKGR are located in pans and valleys, and the soil around these pans is mineral rich, which means that the grass growing here is highly nutritious. As an added bonus, these grasslands have few trees and shrubs, which means that herbivores can spot predators coming from a good distance. The combination of water, high-quality food, and limited predation risk makes these pans highly attractive for wildebeest.

However, during the dry season (when the pans would have dried up, historically), the wildebeest have little choice but to stay close to the pans, as water is pumped into them from boreholes. As the grass around the pans dries up, the amount of food available for the wildebeest dwindles. In the late dry season, daytime temperatures soar to over 40 degrees Celsius, making it too hot for wildebeest to graze in the middle of the day.

The research team wanted to know what these herds would do in the face of declining food, and they predicted that they would start to feed at night during the hottest, driest time of the year. This would make them extremely vulnerable to nocturnal predators, but it could be their only option. Contrary to predictions, wildebeest chose rather to hunker down near their favoured water points day and night. They moved much less in the hot dry season than they did at other times of the year, most likely a strategy to conserve energy while they wait for the first rains.

Blue wildebeest are a water-dependent species, and waterholes such as this one in the CKGR are kept full year-round by pumping water from underground. © Moses Selebatso

The researchers found yet another reason to worry about the effect of pumped waterholes on wildebeest and other wildlife in the Kalahari. They tested the water quality in 12 waterholes throughout the CKGR and Khutse GR. Coming from deep ground water, rather than rainfall, eight of these water points failed the overall water quality test developed for livestock (similar standards for wildlife are unavailable). Even more disconcerting, three of the water points had toxic levels of lead, and four had toxic levels of arsenic. To what extent the wildebeest herds that rely on these waterholes are affected by the poor water quality remains unknown, but it is likely to hamper their ability to survive and reproduce.

Interestingly, one herd of wildebeest monitored during this study behaved entirely differently to the others. At the onset of the dry season they started to move south, away from the pans in the north. Southern CKGR has no pumped waterholes, yet this herd spent the early (cold) dry season in this area. Towards the latter part of the dry season, as temperatures increased, with associated increases in heat and water stress levels, the wildebeest headed even further south, entering the Khutse Game Reserve and neighbouring Wildlife Management Areas. The herd did not visit any known source of water, and the researchers explained this herd’s survival by showing that they eat water bearing plants such as tsamma melons and gemsbok cucumber. These plants are well known as a source of moisture for a host of other desert-dwelling animals (e.g. gemsbok), and this study further confirms the value of these plants to wildebeest in the Kalahari. 

Some wildebeest in the Kalahari use water-bearing plants like gemsbok cucumber (inset) to survive the dry season, rather than staying around pumped waterholes. © Moses Selebatso

This fascinating finding poses a number of questions about artificially maintaining water points. Does the provision of water through the dry season discourage wildebeest migration, to their detriment? Are the migrating wildebeest maintaining better body condition by migrating, even though they are not conserving their energy? Are the sedentary wildebeest damaging the grasslands they rely on by grazing them throughout the year, rather than migrating? Are the wildebeest that do not use waterholes in the dry season healthier than the others, which may be affected by poor water quality? What is the future of wildebeest in this continually changing landscape, with its associated human interventions? Dr. Selebatso and his team will no doubt seek answers to these questions through further research.

One potentially critical problem with artificial water points was clearly demonstrated during their 2011-2014 study. “Four of the water pumps broke down in different times during our study period, causing the water in these pans to dry up,” explains Dr. Selebatso, “this led to seven of our ten study animals walking long distances to find water, five of which died in the process.” Meanwhile, the wildebeest herd that adapted by migrating were not affected by water pump failures. This is an important lesson for managing protected areas: once humans have intervened, animals adapt to the new conditions, and any changes in those interventions could have negative repercussions. Maintaining artificial water points has now become essential for wildebeest that have lost their ability to migrate.

Lead researcher Dr. Moses Selebatso inspects the carcass of a blue wildebeest; his research shows that water holes drying up in the Kalahari can lead to increased mortalities of this species. © Thandi David

Taking a step back from the CKGR, the researchers considered how wildebeest survive in other parts of the Kalahari. Considering the importance of natural pans and the nutrient-rich grasses surrounding these pans, another region has been earmarked as vitally important for wildebeest. This area, known as the Kalahari Schwelle, is located just to the north of the Kgalagadi Transfrontier Park. Dr. Selebatso explains: “The mineral-rich grasslands are extremely important for wildebeest, especially lactating or pregnant females, yet this area lies outside the Park. We know from game counts that more wildebeest occur here than anywhere else in the drylands of the Kalahari. Keeping this particular region free of fencing, and limiting livestock numbers is therefore critical for the wildebeest in this area.”

The land-use management strategies of the past were implemented without knowing the full negative repercussions they would have on wildebeest and other water-dependent herbivores. Furthermore, livestock-based land uses were more lucrative than wildlife-based uses at that time. Today, with the rise of high-end ecotourism ventures, Botswana’s wildlife-based tourism sector brings more money into the economy than the livestock sector. Furthermore, according to Dr. Selebatso, “Wildlife conservation is comparatively cheaper than livestock management in these fragile ecosystems.”

The future of the Kalahari ecosystem can be positive, both in terms of economic return and biodiversity conservation, if land use plans make full use of the knowledge gained from important studies such as these done by Dr. Selebatso and his colleagues. Wildebeest, like many other Kalahari residents, are tough and adaptable, yet still vulnerable to human decision-making. Their future is in our hands.

By Gail Potgieter

To find out more about Kalahari Research and Conservation, click here. Dr. Moses Selebatso provided valuable input for this article. This important study was funded by Denver Zoo Foundation, SAVE Wildlife Conservation Fund, Comanis Foundation, Kanabo Conservation Link, Wilderness Wildlife Trust, and Office of Research and Development (University of Botswana).

Friday 23 February 2018

How to Balance Biodiversity Conservation and Large Elephant Numbers in Botswana: No Extra Water for Elephants!

Botswana's researchers contribute to the debate surrounding large elephant populations and their impact on the environment in southern Africa.

An elephant in the Mababe floodplains in northern Botswana. Photo By Gail C. Potgieter.
Elephants: the majestic gentle giants of the African savannah. Their enormous intelligence and close family bonds fascinate safari goers and scientists alike. Whilst strolling through the bush, they shovel masses of grass into their mouths, and occasionally bump into the odd tree – effortlessly breaking large branches and even pushing the whole thing over. Elephants are awesome creatures, and even lions keep a respectful distance from these megaherbivores.

All of the unique characteristics that put elephants at the top of the must-see list for many international visitors also serve to create controversy and management headaches among conservationists. These giants need gigantic amounts of space and natural resources – at one point in history this was not a problem, as all of Africa except the Sahara was available to them. Today’s remnant populations have been constricted to relatively small areas, which are often fenced and managed by humans. Their food requirements, however, have not changed – they need to eat anywhere between 140 and 490 kg of plant matter every single day! Additionally, they are highly dependent on water, and each bull elephant will drink up to 120 litres per day.

In short, the impact of elephants does not go unnoticed in the African savannah. Certainly, the effects of Botswana’s 130,000 pachyderms are easy to see from just a cursory glance at the landscape. Broken and uprooted trees are the most obvious signs of elephants, but they also eat huge amounts of grass and other small plants (called forbs). Whilst elephants mainly eat grass and forbs in the wet summer season, they rely on trees (leaves, bark, roots) to get them through the dry winter season. Trees are therefore most vulnerable to being de-barked and uprooted in the late dry season.

These facts leave us in no doubt about the enormous impacts that elephants have in any ecosystem where they occur. Although Botswana’s elephant population is not overly restricted by fences (as are those in many of southern Africa’s protected areas), they seem to concentrate in northern Botswana. In particular, huge herds of elephants congregate by the Chobe River during the dry season – a spectacular sight for tourists, but a cause for concern among ecologists.

A Mopane woodland in October 2010 at a location in northern Botswana. Photo by Christiaan Winterbach.
The same Mopane woodland in October 2013 showing large-scale elephant damage. Photo by Christiaan Winterbach.

The Elephant Debate

The question that many ask is: Are there too many elephants in Botswana? This question, however, begs another more critical question – how do we know how many is too many? This latter question is subject to enormous debate within southern Africa, which focuses on the ecological carrying capacity of certain National Parks for elephants. Carrying capacity is often seen as a ‘golden number’ of elephants, beyond which they begin to overuse the local ecosystem, thus damaging it and negatively affecting other species. On the other side of the debate, some point out that whilst elephants seem to cause enormous destruction in the immediate vicinity of waterholes, this does not necessarily mean that they are destroying the entire ecosystem.

These debates are far from merely academic. If those warning that there are too many elephants for ecosystems to support are right, then something needs to be done before the damage becomes irreparable. What that ‘something’ entails, however, is often too terrible for most elephant-loving people to consider. The large-scale elephant culling operations suggested by some are not a popular solution, unsurprisingly. Other options, like translocation and contraception are more palatable, but too expensive to be used on large elephant populations. In particular, the sheer size of Botswana’s elephant population means that none of these solutions is currently practical – including culling. However, some commentators warn of catastrophic consequences for all species if nothing is done, and soon.

A Local Scientific Contribution

Avoiding emotionally charged debates based on little more than informed opinion, researchers from Botswana decided to tackle the critical elephant question head-on. Dr. Keoikantse Sianga and Dr. Richard Fynn of the Okavango Research Institute (a specialized department of the University of Botswana) joined forces with three Dutch researchers from Wageningen University in a vegetation study focusing on a large natural area called the Savuti-Mababe-Linyanti Ecosystem. This enormous area of nearly 30,000 square kilometres lies between the Okavango Delta, the Mababe Depression and the Linyanti Swamps, and therefore hosts a healthy proportion of Botswana’s elephants.

The researchers doing field work. Note the elephants in the background! Photo by Jip Vrooman.

They chose this particular area as it is almost untouched by human management efforts, unlike most other locations in southern Africa. Only one pan is artificially pumped to maintain water throughout the dry season in their entire study area, and there are no fences within the area to inhibit elephant movement. They could therefore ask: in the virtual absence of human interference, are there too many elephants for this ecosystem to support? Additionally, this important work reveals how elephants naturally affect their habitat, thus providing a baseline to compare with other areas that are heavily managed. Whilst not resolving the elephant debate, this scientific knowledge can help wildlife managers in southern Africa to better understand the problem and consequently make better decisions to resolve it.

Rather than trying to calculate the ‘golden number’ of elephants that can be supported by the ecosystem, the research team sought to answer the underlying question – is the current elephant population is actually damaging the ecosystem? They viewed ecosystem health as its ‘heterogeneity’, which is an indication of how many different habitats are available for different species (known as ecological niches). A heterogeneous ecosystem has many different species of trees and grass, all growing to different heights. Some grazing herbivores prefer tall grass, whereas others prefer short grass; some bird species prefer dense shrubs to live and nest in, whereas others prefer tall trees. Consequently, to support a large variety of animals, you need a variety of different habitats, which can be measured directly by looking at the plants.

If the plants in the Savuti-Mababe-Linyanti ecosystem were all the same species, or all the same height, it would indicate a serious problem. Something (e.g. elephants) would be ‘homogenising’ the ecosystem; i.e. reducing the number of habitats available for other species. If, however, the system is still heterogeneous (i.e. containing many plant species of different heights), then it can still harbour a good diversity of species.

Understanding elephant behaviour and biology helped the team develop a suitable way to test how elephants are influencing the ecosystem. Although elephants can traverse great distances if they want to, they are highly dependent on water and must drink daily. During the wet season, water dependence is not an issue, as temporary natural pans fill up with water, thus allowing many elephants to move away from permanent water sources and use most of the ecosystem. However, in the dry season these pans dry up, and elephants have to stay close enough to rivers and permanent lakes to return to them on a daily basis. The average distance that bull elephants will stray from water in a day in search of food is around 15 kilometres, whereas herds of females and their young ones will only go as far as 5 kilometres. Consequently, the largest elephant impact will be found less than 5 km from permanent water, with less impact in the 5-15 km zone, and minimal impact over 20 km from water (only accessible to elephants during the wet season).

The research team investigated the species diversity and plant height of trees, grasses, and forbs in each of these three zones on four different routes through their study area. They also counted the dung of elephants and other herbivores to find out how much these places were visited by herbivores. Finally, they obtained fire records for the last 15 years to ensure that the effects of fire could be separated from the effects of elephants and other herbivores.

One of the researchers measuring tree height. Photo by Jip Vrooman.

Their results revealed that, rather than irreparably damaging the ecosystem, elephants actually help maintain heterogeneity by improving grass and forb species richness in the zone closest to permanent water. These grasses were kept short through year-round grazing by elephants and other herbivores. In contrast, the zone furthest from water was dominated by high-quality long grasses, which are preferred by species such as sable and roan antelope. These results were found in the vegetation type known as sandveld, which is especially important for grazers, as it supports a rich diversity of grass species.

Similarly, trees were taller in the zones far from water than in the zone less than 5 km from water. During the dry season, elephants use trees more heavily and it is therefore not surprising that the trees closest to permanent water are frequently broken and thus kept in a shortened state. They found this trend for the two most common tree species in the ecosystem – Mopane and Terminalia sericea (silver cluster leaf). Although short, stumpy shrubs look less attractive to us than tall trees, it is important that ecosystems contain both shrubs and trees.

Managing Ecosystem Health in Botswana – Recommendations

The researchers concluded that the large population of elephants in northern Botswana perform a key ecological role by maintaining heterogeneity in the ecosystem. There is, however, one important caveat to this conclusion: this system can continue to sustain large elephant numbers only as long as there are large distances (at least 50 km) between permanent water sources.

The fact that young elephants cannot walk as far as adults between food and water is one of the key natural ways of preventing elephant populations from growing too large. In long dry seasons, adult females are forced to move further away from water to find food, and this may mean that some calves do not survive the dry season. They therefore warn against developing new waterholes in this ecosystem for two reasons. Firstly, the impacts of large elephant herds all year every year would soon turn the whole area into short grass and shrubs with little species diversity, to the detriment of other animals that prefer long grass and trees. Secondly, providing permanent waterholes would remove one of the few natural mechanisms for limiting elephant numbers.

These warnings are not idle, as they build on harsh lessons learned in other places. It is also about more than just elephants. Studies in the Kruger National Park show that when waterholes were developed throughout the park (such that the average distance to water in the dry season was a mere 6 km), the habitat for sable and roan shrank, as water-dependent grazers (e.g. zebra and buffalo) moved in to previously waterless regions. The ultimate result was a tragic population crash of both species, and very few can be found in the Kruger today. Predators like lions are also favoured by increasing waterholes, as many of their preferred prey species are water dependent. Although this sounds great for tourism, larger lion populations may have contributed to the crash of roan and sable, and are likely to reduce the number of African wild dogs. These are just two examples of the unintended negative consequences of artificial waterholes. Northern Botswana currently hosts healthy populations of roan, sable, and African wild dogs. Lessons learned from the Kruger should therefore provide major pause for thought before developing waterholes in this region.

A family of sable antelope in the wild in northern Botswana. Photo by Rob Thomson.
Similarly, the researchers warn that the waterholes in the Chobe region are the primary cause for large-scale elephant damage seen far beyond the Chobe River. However, the tall trees growing along the Chobe River (a vegetation type known as ‘riparian woodland’) are a special cause for concern, as elephants gather in high numbers along the riverfront in the dry season. This area lacks the tall grass and sedges that can be found year round on the floodplains in the Okavango Delta, which means that the elephants along the Chobe River rely almost entirely on trees – to the detriment of riparian woodland. One of the research team, Dr. Richard Fynn, suggests: “In areas without extensive tall grass floodplains, the only hope for protecting riparian woodlands is to find ways of preventing elephants from staying too long in riparian vegetation during the dry season, or by protecting specific trees from elephants.”

The researchers point out that fencing that restricts elephant movements during the wet season is also likely to increase pressure on the ecosystem. Rather than allowing the short grasslands near permanent water to rest during the dry season, the megaherbivores (elephants and buffalo) are forced to use these grasses heavily throughout the year, rather than migrating to other areas.

Artificial water holes and barriers to elephant movement (such as fences) are thus ultimate causes of ecosystem damage, rather than the elephants themselves, which simply respond to the available resources. Simply removing many elephants will not solve the underlying problem, so the population will keep rebounding and there will be an endless battle for the health of the ecosystem.

For the moment, the Savuti-Mababe-Linyanti Ecosystem remains intact. However, the researchers recommend that this area should be carefully monitored, and that pumping new waterholes should be tightly regulated. Furthermore, the prevalence of current waterholes in the Chobe Region (east of their study area) and threats to elephants beyond Botswana’s borders that restrict elephants to northern Botswana are key issues that need to be addressed. Allowing elephants to move freely over large, unfenced areas is a regional challenge that needs to be discussed between Botswana and neighbouring countries. Perhaps it is time the debate around elephants evolves from carrying capacity numbers and elephant management to ecosystem health and landscape management.

By Gail Potgieter

Elephants enjoying a seasonal pan during the late wet season. When this pan dries up, they will move to permanent water sources in northern Botswana. Photo by Gail Potgieter.

Full article reference: Sianga, Keoikantse; van Telgen, Mario; Vrooman, Jip; Fynn, Richard W.S. & van Langevelde, Frank. (2017). Spatial refuges buffer landscapes against homogenisation and degradation by large herbivore populations and facilitate vegetation heterogeneity. Koedoe, 59(2),1-13.