If you live near or have visited Cape Town’s outskirts – where urban and natural areas meet – you might have been lucky enough to see a caracal. These adaptable, medium-sized wild cats with distinctive long tufted ears are also found in other parts of the African continent, as well as the Middle East, Central Asia and India.
Caracal are the largest remaining predator in Cape Town, the world most biodiverse city. It is estimated that there are around 50-60 caracal left in the Cape Peninsula. Our research so far has shown that the city’s caracals mainly feed on native wild species, such as guinea fowl and vlei rats. And they prefer to hunt their prey close by urban edge — especially in areas where vineyards and wetlands are nearby.
But this choice comes with risks. This means they have to cross roads to reach fragmented habitats; Car collisions are an obvious threat. A less obvious one is Persistent Organic Pollutants or “Forever Chemicals”.
These long-lived, toxic chemicals are largely invisible, traveling through air and water and ending up in even the most remote environments. They affect people and animals health. They have been used in crop protection products, in industry and in construction since the 1940s. These activities release the chemicals into the air, soil and water. There they remain intact for a long time and can spread through natural processes.
These pollutants tend to accumulate in the body tissues of animals — especially predators. Chemicals build up in predators from the prey they eat, a process known as Biomagnification. This means that predators can act as sentinels or as sentinels indicators for the presence, variety and level of pollutants in the environment.
To date, most research on these chemicals has taken place in Europe and North America, with little focus on the Global South. Our research in Cape Town wants to close this gap. We’re investigating how local wildlife can be affected by a particularly toxic class of pollutants called organochlorines. This group of man-made chemicals contains carbon, chlorine, and several other elements. Among them are polychlorinated biphenyls, a group of highly carcinogenic chemicals that were formerly used in many industrial and consumer products.
We studied the diet, hunting behavior and pollution levels of Cape Town’s caracals. Our latest findings show extensive exposure to these chemicals in the city’s complex mosaic of habitats.
Caracals as indicators of environmental health
In collaboration with wildlife ecotoxicologist Rafael Mateo from Universidad Castilla in La Mancha, Spain, we studied how the caracal were exposed to pollutants.
As part of our work, samples were collected from caracal cage traps to monitor their movements with GPS collars. The animals were sedated and blood samples were taken by a veterinarian. We also collected blood and fat samples from dead caracals picked up around Cape Town, mainly animals killed in car collisions.
We tested samples using gas chromatography-mass spectrometry, a method that can detect and quantify pollutant chemicals in tissue samples, even at low levels.
A worrying trend has emerged: caracals often hunt in areas where one exists higher risk of organochlorine exposure. Individuals who hunt closer to dense human populations and in wetlands and vineyards have higher levels of both the insecticide DDT (dichloro-diphenyl-trichloroethane) and polychlorinated biphenyls in their blood and adipose tissue than those who hunt further away.
This connection to vineyards is a trend that we previously picked up on when assessing exposure to another type of pesticide. rat poisons. Caracal hunting in Cape Town’s vineyards, where prey is plentiful, are also likely to be exposed to a cocktail of highly toxic anticoagulant rodenticides.
Caracals using areas with a higher density of electrical transformers had higher exposure to chemicals in the polychlorinated biphenyl group. This is likely due to polychlorinated biphenyls leaching from the coolant fluids used in electrical equipment. The chemicals were banned worldwide in the 1980s and South Africa has committed to phase them out by 2025.
Taken together, our results suggest that many human-modified landscapes may harm wildlife through prior or ongoing use of “forever chemicals.”
what can be done
Although this study is the first of its kind for southern Africa, it adds to the growing evidence that predator indicator species can reveal exposure to pollutants through food webs in human-modified areas.
The cities of the world represent a new type of ecosystem for wildlife. Many species have adapted to these landscapes. In doing so, however, they are brought into contact with invisible risks, such as increased exposure to pollutants.
When a habitat poses both risk and reward, it can be an “ecological trap,” accelerating local extinctions. Ecological traps are also a global problem that requires collective action.
To make cities around the world safer and cleaner, the use of “forever chemicals” must be reduced in line with existing international agreements. Citizens can also reduce their own use of pesticides, particularly rat poison. The cleanup and restoration of urban wetlands could go a long way in removing pollutants from the environment.
People should also take stock of existing chemical use. The safe disposal of obsolete chemicals and obsolete or contaminated equipment is an essential step in reducing spills into natural areas.
These efforts will ensure healthier cities – not just for wildlife, but for people as well. DM
First release of The conversation.
Gabriella Leighton is a Post-Doctoral Fellow at Rhodes University and Jacqueline Bishop is a Lecturer in Conservation Biology at the University of Cape Town.