The Science of Artificial Waterholes for Wildlife
The Take home Message
- Game managers in the western United States commonly build artificial water sources for wildlife, especially game species.
- Artificial water sources are necessary because humans have altered the landscape making it impossible for some animals to find enough water. Unfortunately, artificial water sources also cause substantial ecological problems.
- Scientists and game managers in Africa are decades ahead of us in the United States in recognizing the problems associated with artificial water sources and devising strategies to maximize the benefit of artificial water sources while minimizing the costs.
The full story
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Artificial water sources like water catchments, cattle tanks, and boreholes are a controversial topic in the United States. Most are installed by landowners and ranchers, but management agencies in the western United States also install them for wildlife. Some state agencies, like Arizona Game & Fish, are serious about artificial water sources and go to rather extreme measures to maintain them. If you regularly hunt sage-grouse or big game or other arid-adapted species in the western United States, there's a good chance you've hunted over or near an artificial water source.
In the United States, the popularity of using artificial water sources for wildlife has fluctuated over the years. Providing permanent water sources seems like an obvious way to help wildlife in hot and dry environments, and in some cases they are. Without artificial water sources, many animals could no longer survive in the arid deserts and grasslands where they evolved. They are absolutely necessary to maintain something resembling natural animal assemblages in many places. However, like all other human actions, artificial water sources do have impacts on natural environments. They can cause changes in vegetation. Wildlife distribute differently on the landscape when artificial water sources are available. Water sources change how herbivores forage and how carnivores hunt those herbivores. The effects can be surprisingly far-flung from the site of the water source. |
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Both the positives and negatives of artificial water sources have attracted the attention of scientists for decades. While there has been some quality science done on the effects of artificial water sources on natural ecosystems in the United States, most of the best work on this topic comes from Africa. Why has so much great science been done on artificial water sources in Africa? It probably comes down to opportunity for researchers to work in areas where artificial water sources are common. Artificial waterholes (which is what they are called in South Africa) have long been a standard management practice across most of the arid regions in sub-Saharan Africa.
It’s not uncommon for big-game hunts in southern and eastern Africa to occur around waterholes. Most ecotourism operations in arid Africa, both private and governmental, make liberal use of waterholes. Many of the stunning photos you see on this page were taken around waterholes. Because waterholes have been used so widely, and for so long, African scientists and game managers seem to have a much more thorough catalog of knowledge about them than we do in the United States. With that in mind, I want to introduce the science of artificial waterholes in Africa and how we can use the knowledge gained in Africa in the United States.
It’s not uncommon for big-game hunts in southern and eastern Africa to occur around waterholes. Most ecotourism operations in arid Africa, both private and governmental, make liberal use of waterholes. Many of the stunning photos you see on this page were taken around waterholes. Because waterholes have been used so widely, and for so long, African scientists and game managers seem to have a much more thorough catalog of knowledge about them than we do in the United States. With that in mind, I want to introduce the science of artificial waterholes in Africa and how we can use the knowledge gained in Africa in the United States.
In many African parks and reserves, water-dependent species are usually easy to find near artificial waterholes.
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Kudu are rarely far from water.
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Red-billed queleas and Scaly-feathered finches flock to artificial waterholes by the thousands. Drinking regularly allows these species to thermoregulate in extreme environments.
Simply documenting whether or not animals use waterholes is important, but not sufficient to really understand both the positives and negatives of waterholes as a management strategy. The management implications of installing water sources receive most of the attention, but to fully understand how water affects ecosystems, I think it's necessary to understand the physiology of arid-adapted animals as well.
First, let’s cover why so many animals need artificial waterholes when they clearly weren’t necessary across evolutionary time. All living things obviously need water. Most physiological functions require water. Breaking down energy, removing waste from the body, balancing salts, transporting things around the body, and maintaining a favorable body temperature (termed thermoregulation) all require water . In hot, dry environments where artificial waterholes are most common, the role of water in thermoregulation stands out as vitally important.
If air temperature is higher than an animal’s body temperature, the animal will absorb heat and its body temperature will rise. Add solar radiation, and an animal can quickly overheat. Some species avoid the overheating problem by concentrating activity at night and spending their days in burrows or rocky areas where it is cooler. Many birds and large mammals don’t have this option. Instead, they are forced to either deal with increased body temperatures or use water to lose heat through evaporation.
There are some desert animals able to survive amazingly high body temperatures. A research team based in South Africa has documented desert birds that can withstand body temperatures of over 120°F (49°C). Even a few desert mammals allow their body temperature to creep up near 110°F (43°C) during the hot dry season. A human body would quickly shut down at body temperatures of 110°F, and survival would be unlikely if those body temperatures persisted for more than a few minutes.
While humans are far more sensitive to high body temperatures than desert species, no bird or mammal could survive these extreme body temperatures for extended periods. Most animals prefer to remain cooler when possible, but at very high temperatures, the only mechanism to lose heat is evaporation, which requires water. As water evaporates, it takes energy (heat) with it. In humans, we lose heat through evaporation mostly by moving water to the surface of the skin in the form of sweat. Most animals don't sweat, so they lose heat through evaporation of water from the lungs, inside of the nose, or directly across the skin. Many desert animals can, if they have sufficient water, offload enough heat through evaporation to maintain relatively normal body temperatures even when exposed to temperatures of 120°F or more.
First, let’s cover why so many animals need artificial waterholes when they clearly weren’t necessary across evolutionary time. All living things obviously need water. Most physiological functions require water. Breaking down energy, removing waste from the body, balancing salts, transporting things around the body, and maintaining a favorable body temperature (termed thermoregulation) all require water . In hot, dry environments where artificial waterholes are most common, the role of water in thermoregulation stands out as vitally important.
If air temperature is higher than an animal’s body temperature, the animal will absorb heat and its body temperature will rise. Add solar radiation, and an animal can quickly overheat. Some species avoid the overheating problem by concentrating activity at night and spending their days in burrows or rocky areas where it is cooler. Many birds and large mammals don’t have this option. Instead, they are forced to either deal with increased body temperatures or use water to lose heat through evaporation.
There are some desert animals able to survive amazingly high body temperatures. A research team based in South Africa has documented desert birds that can withstand body temperatures of over 120°F (49°C). Even a few desert mammals allow their body temperature to creep up near 110°F (43°C) during the hot dry season. A human body would quickly shut down at body temperatures of 110°F, and survival would be unlikely if those body temperatures persisted for more than a few minutes.
While humans are far more sensitive to high body temperatures than desert species, no bird or mammal could survive these extreme body temperatures for extended periods. Most animals prefer to remain cooler when possible, but at very high temperatures, the only mechanism to lose heat is evaporation, which requires water. As water evaporates, it takes energy (heat) with it. In humans, we lose heat through evaporation mostly by moving water to the surface of the skin in the form of sweat. Most animals don't sweat, so they lose heat through evaporation of water from the lungs, inside of the nose, or directly across the skin. Many desert animals can, if they have sufficient water, offload enough heat through evaporation to maintain relatively normal body temperatures even when exposed to temperatures of 120°F or more.
Some species, like gemsbok, will drink at artificial waterholes, but are extremely resistant to dehydration and can go long periods without water.
Even though many species can use extensive evaporative water loss to maintain body temperature, not all desert birds and mammals do so. Some species are heavily water dependent, while others are not. There are pros and cons to each strategy. Water-dependent species usually have high rates of evaporative water loss and can therefore maintain body temperature even in very hot conditions. However, they are constrained to areas with reliable water, and may have to travel long distances throughout the season to find water. They must have reliable food sources near the water and they risk attracting predators if they stay in one place too long. Conversely, water-independent species can live far away from water or meander across the landscape in the search of food and to avoid predators. However, they can't rely on evaporative water loss and therefore can't withstand very hot conditions.
Unfortunately, climate change is likely to make thermoregulation and survival even harder for desert species. Many of the already hot and dry deserts are becoming hotter and drier. As temperatures increase, water-independent species may not be able to survive because they can't withstand very hot temperatures. Water-dependent species might survive longer if they have ready access to waterholes, but at some point, the temperatures will become hot enough that even water-dependent species simply won’t be able to drink enough water to maintain body temperatures below lethal levels. We are already seeing mass die-offs of desert species during heat waves in Australia even with access to water. Artificial waterholes might be a key management tool in the future to mediate some of the negative effects of climate change on desert animals.
So, water is vitally important for thermoregulation and therefore survival of many species in deserts and grasslands. Water also plays a huge role in the ecology of animals in arid environments. Before humans chopped up the landscape with cities, roads, and fences, water-dependent species would have moved long distances in search of water. During dry seasons, those species would have concentrated on rivers and floodplains where there was a permanent water source. During wet seasons, some would have dispersed across the landscape because ephemeral (temporary) water sources were available. As humans have changed the landscape, many animals have lost access to water sources during parts of the year. In some places, large animals simply can’t roam wide enough to find water all year. Even in huge parks, like the Kgalagadi Transfrontier Park in South Africa and Botswana, large water-dependent mammals can only survive because of waterholes. During the dry season, natural water sources are just too scarce within the confines of the park.
Unfortunately, climate change is likely to make thermoregulation and survival even harder for desert species. Many of the already hot and dry deserts are becoming hotter and drier. As temperatures increase, water-independent species may not be able to survive because they can't withstand very hot temperatures. Water-dependent species might survive longer if they have ready access to waterholes, but at some point, the temperatures will become hot enough that even water-dependent species simply won’t be able to drink enough water to maintain body temperatures below lethal levels. We are already seeing mass die-offs of desert species during heat waves in Australia even with access to water. Artificial waterholes might be a key management tool in the future to mediate some of the negative effects of climate change on desert animals.
So, water is vitally important for thermoregulation and therefore survival of many species in deserts and grasslands. Water also plays a huge role in the ecology of animals in arid environments. Before humans chopped up the landscape with cities, roads, and fences, water-dependent species would have moved long distances in search of water. During dry seasons, those species would have concentrated on rivers and floodplains where there was a permanent water source. During wet seasons, some would have dispersed across the landscape because ephemeral (temporary) water sources were available. As humans have changed the landscape, many animals have lost access to water sources during parts of the year. In some places, large animals simply can’t roam wide enough to find water all year. Even in huge parks, like the Kgalagadi Transfrontier Park in South Africa and Botswana, large water-dependent mammals can only survive because of waterholes. During the dry season, natural water sources are just too scarce within the confines of the park.
Carnivores often take advantage of congregations of water-dependent species like buffalo to maximize hunting success.
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Caracals make good use of the concrete structures around artificial waterholes to stalk and catch elusive prey, like doves.
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Scavengers are never far from areas where herbivores congregate and carnivores hunt.
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This leads to the second interesting part of the science of artificial waterholes, which are studies on the fairly dramatic effects waterholes sometimes have on the landscape. Artificial waterholes functionally replace the ephemeral water sources spread across the landscape that historically would have been visited periodically by mammals and birds. However, unlike those ephemeral water sources, artificial water sources are permanent and always available. They’re also often sited to maximize opportunities for hunting or ecotourism, so they usually aren’t in the same location as ephemeral water sources.
Waterholes dramatically alter the distribution of herbivores in some systems. The permanent nature of artificial waterholes means that animals are constantly visiting the same spot. Water-dependent herbivores like buffalo, kudu, and wildebeest congregate around waterholes instead of dispersing across the landscape. Where there are herbivores, carnivores follow. Most lion kills occur near waterholes, and therefore lions often choose prey that are water-dependent. For this reason, artificial waterholes might be a boon for water-independent species if lions, cheetahs, and leopards focus on the water-dependent species. Waterholes can also become stagnant and spread disease through populations of water-dependent species. Artificial waterholes literally change the food web.
Waterholes dramatically alter the distribution of herbivores in some systems. The permanent nature of artificial waterholes means that animals are constantly visiting the same spot. Water-dependent herbivores like buffalo, kudu, and wildebeest congregate around waterholes instead of dispersing across the landscape. Where there are herbivores, carnivores follow. Most lion kills occur near waterholes, and therefore lions often choose prey that are water-dependent. For this reason, artificial waterholes might be a boon for water-independent species if lions, cheetahs, and leopards focus on the water-dependent species. Waterholes can also become stagnant and spread disease through populations of water-dependent species. Artificial waterholes literally change the food web.
Effects of artificial waterholes aren't limited to animals. In areas with dense populations of large mammals, the vegetation around the waterholes takes a beating and large areas can be completely cleared of vegetation. Most of the plants in arid regions evolved to withstand periodic grazing or browsing as animals moved through, not prolonged heavy pressure like that caused by animals around waterholes. When these areas are cleared, extensive erosion can occur. Dense networks of game trails form around artificial waterholes and can fragment vegetation for hundreds of yards into the bush. High densities of elephants around waterholes can lead to long term shifts from woodlands to shrubby areas as elephants do considerable damage to trees while foraging. In some places, you’ll find rings of trees growing around waterholes in locations that would otherwise be desert or grassland. Artificial waterholes literally change the landscape.
These effects were recognized decades ago by scientists and managers in African parks and game reserves. For example, in Kruger National Park, South Africa, a concerted effort began in the 1990's to balance the water needs of the animals and the ecotourism benefits of concentrating animals in predictable locations against the ecological damage caused by artificial waterholes. In Kruger, and across African parks, many artificial waterholes are being closed or removed completely to try to reach the appropriate balance.
These effects were recognized decades ago by scientists and managers in African parks and game reserves. For example, in Kruger National Park, South Africa, a concerted effort began in the 1990's to balance the water needs of the animals and the ecotourism benefits of concentrating animals in predictable locations against the ecological damage caused by artificial waterholes. In Kruger, and across African parks, many artificial waterholes are being closed or removed completely to try to reach the appropriate balance.
Overhead view of an artificial waterhole on a private reserve in the Kalahari Desert of South Africa. You can clearly see the effect of the waterhole (a rectangular concrete pool) on the area immediately surrounding it. All the vegetation has been trampled in an area about 140 x 85 yards (130 x 75 meters). If you look beyond that circle, you can see clearly defined game trails.
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Constant pressure from large herbivores leads to trampled vegetation and often erosion.
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Many parks open or close the boreholes that feed artificial water sources, as I'm sure this lion cub was disappointed to discover.
There has also been recent recognition that many of the problems associated with artificial waterholes in African parks come from their permanent nature. Water availability in arid regions tends to vary across space and time. In moderately or seasonally arid regions, like where Kruger is located, the large rivers hold water all year, but water would otherwise be scarce on the landscape for much of the year. In arid and hyper-arid regions, like the Kalahari Desert, even the large rivers are dry except immediately following rain. In some places, riverbeds can remain dry for years or decades on end. Spatially and temporally variable water is natural in arid regions and the plants and animals in arid regions are adapted to survive and flourish under those conditions. While human-caused changes to the landscape mean we'll never be able to perfectly mimic natural variability in water availability, some parks are making efforts to open and close waterholes periodically to allow natural vegetation an opportunity to recover. It's a good first step. Those parks are still working to find the appropriate management scheme for artificial waterholes, but they are decades ahead of us in the United States in this regard.
So, how can the hunter, rancher, or game manager in the western United States take advantage of the knowledge gained from decades of research in Africa? Most importantly, I hope we can recognize in the United States that artificial water sources should be viewed as a necessary evil. Arid-adapted plants and animals only need artificial water sources because humans have changed the landscape and hydrology in such a way that natural water is not available to some animals. We're now exasperating the problem through climate change. Providing artificial water sources should thus be viewed as a last-ditch effort to counter environmental damage, not proactive management.
In the western United States, it seems that most artificial water sources are installed for livestock or game species, like bighorn sheep. It is certainly possible this singular focus will allow managers to take a myopic view of what constitutes successful provisioning of artificial water sources while ignoring the ecological problems. If the target game species visits the water source, it is considered a success. In African parks, it was a heavy focus on ecotourism and making animals easily viewable and huntable that led them to take a myopic view of success for many decades. I hope we can learn from our African colleagues that more widely distributed water isn't always the answer. If we take this lesson seriously, we can avoid many of the problems caused by oversaturation of the landscape with artificial water sources. Kruger National Park has spent decades correcting this mistake.
I reiterate that in many places, artificial water sources are a necessity if roads, fences, or farms preclude animals from ranging far enough to find natural water sources or if climate change further dries out arid regions. However, installing water sources only to increase hunting opportunities can lead to a host of ecological problems. Artificial water sources should ideally be installed and managed to mimic natural water availability when possible. It will likely mean that game managers have to work with hydrologists to determine how water would vary temporally and spatially on the landscape. Such information might drive decisions to site water sources in hard-to-reach places or only open them periodically. It will certainly take more time and effort than opening a water catchment and walking away. We have the knowledge to do better with artificial water than we have in the past. Now, it's just a matter of putting that knowledge into practice.
So, how can the hunter, rancher, or game manager in the western United States take advantage of the knowledge gained from decades of research in Africa? Most importantly, I hope we can recognize in the United States that artificial water sources should be viewed as a necessary evil. Arid-adapted plants and animals only need artificial water sources because humans have changed the landscape and hydrology in such a way that natural water is not available to some animals. We're now exasperating the problem through climate change. Providing artificial water sources should thus be viewed as a last-ditch effort to counter environmental damage, not proactive management.
In the western United States, it seems that most artificial water sources are installed for livestock or game species, like bighorn sheep. It is certainly possible this singular focus will allow managers to take a myopic view of what constitutes successful provisioning of artificial water sources while ignoring the ecological problems. If the target game species visits the water source, it is considered a success. In African parks, it was a heavy focus on ecotourism and making animals easily viewable and huntable that led them to take a myopic view of success for many decades. I hope we can learn from our African colleagues that more widely distributed water isn't always the answer. If we take this lesson seriously, we can avoid many of the problems caused by oversaturation of the landscape with artificial water sources. Kruger National Park has spent decades correcting this mistake.
I reiterate that in many places, artificial water sources are a necessity if roads, fences, or farms preclude animals from ranging far enough to find natural water sources or if climate change further dries out arid regions. However, installing water sources only to increase hunting opportunities can lead to a host of ecological problems. Artificial water sources should ideally be installed and managed to mimic natural water availability when possible. It will likely mean that game managers have to work with hydrologists to determine how water would vary temporally and spatially on the landscape. Such information might drive decisions to site water sources in hard-to-reach places or only open them periodically. It will certainly take more time and effort than opening a water catchment and walking away. We have the knowledge to do better with artificial water than we have in the past. Now, it's just a matter of putting that knowledge into practice.