Rat poisons used in homes, businesses and on farms are moving into South Africa's wildlife, according to new research from the Urban Caracal Project, a key research and education initiative based in the Institute for Communities and Wildlife in Africa (iCWild) at the University of Cape Town, together with international collaborators from the Institute for Game and Wildlife Research (IREC) and the Institute of Environmental Assessment and Water Research (CSIC) in Spain.
In the paper, published in Environmental Pollution, researchers analysed liver samples from 102 caracal mortalities collected over ten years, mainly from car collisions, revealing highly toxic anticoagulant rodenticides (ARs) in 78% of samples analysed. Most individuals were exposed to at least three different compounds, but some were found to have up to six compounds in a single sample. Older animals had higher burdens, supporting the study's conclusion that caracal experience repeated, long-term cumulative exposure to ARs in the study area.
The research found that highly toxic second-generation compounds dominated the population's exposure profile. Anticoagulant rodenticides are chemical poisons that inhibit blood from clotting. They work by blocking vitamin K cycle in the liver, causing fatal internal bleeding in target rodents as well as non-target mammals and birds that are exposed to lethal doses. First-generation ARs generally require repeated feeding and break down faster in animal tissues, while more commonly used second-generation products, or SGARs, were developed in the 1970s partly to overcome resistance to older poisons. SGARs are more potent, can be toxic after a single feeding, and remain in the animal's tissues for longer. However, even a toxic dose can take a while (up to two weeks) to kill a poisoned animal. Because death is delayed, rodents may continue feeding and carry high concentrations that subsequently poison non-target predators and scavengers.
"Caracals are red warning lights at the top of the food web," comments Dr Gabriella Leighton, the lead author and currently a lecturer at Stellenbosch University's Department of Botany and Zoology. "Caracals move easily through natural areas, farms and suburbs and eat many kinds of prey. What accumulates in their bodies provides a broader picture of contamination across the landscape." While felid species such as caracals are very tolerant to exposure to ARs, such that they rarely die from exposure, the authors stress that "the sublethal effects of ARs are currently unknown for caracals". However, subadult caracals in poorer condition carried higher loads.
As apex predators in the urban food web, caracals are valuable indicator species: animals that reveal wider environmental contamination. Previous research by the Urban Caracal Project also documented AR exposure in other carnivore species in and around Cape Town including otters, large-spotted genets, mongooses, honey badgers and owls. Importantly, the current study reveals several hotspots of poison risk with higher numbers and concentrations of rodenticides in caracals using vineyards, wetlands, greener urban areas, and areas with more restaurants, cafés and other food outlets.
Research on wild carnivores globally gives cause for concern. In another wild cat, the North American bobcat, exposure has been associated with inflammation, suppressed immune responses and changes in gene activity affecting immune defence, skin integrity and toxin processing – symptoms that are correlated with greater disease susceptibility, particularly fatal mange. Reported effects in other wildlife species include impaired clotting, internal bleeding, poorer condition, lethargy, reduced movement and weakened reflexes.
These may leave animals less able to fight infection, hunt or avoid vehicles, but this has yet to be demonstrated in caracals.
"This is not only about animals dying after a large dose," says Dr Laurel Serieys, the senior author on the paper. "Repeated lower exposure may quietly weaken animals and make it harder for them to cope with disease and other urban dangers."
While the study could not trace caracal contamination events to individual brands, consumers should note the active ingredient and registration number on packaging, as formulations can change and some compounds are in the process of being phased out but nonetheless remain on shelves. Products to look out for that contain anticoagulant poisons detected in caracals include: Rattex (Tiger Brands), Kombat, and Jaguar (MC Pharma), which all contain brodifacoum, a highly potent SGAR. Other examples include Tomcat (MC Pharma) and Scientific Supa-Kill containing bromadiolone; and Racumin (Bayer Group) containing first-generation compounds like warfarin and coumatetralyl. Consumers should avoid anticoagulant products, especially SGARs, and use non-poison methods whenever possible. Importantly, there are no "wildlife-safe" anticoagulant poisons, so always check the packaging if trying to find a poison to control rodents.
Prevention should come first: secure food and waste, seal entry points, improve home and restaurant waste management, and use snap traps. Where poison is necessary, it should only be used briefly by trained operators in tamper-resistant stations and monitored for efficacy. Loose bait should never be scattered outdoors, and rodent carcasses and unused bait should be safely removed.
South African regulations require high-risk pest-control poisons to be restricted by how they are displayed, distributed and used, and who may use them. They also require reporting of annual national sales totals, but national totals alone cannot reveal who bought a poison, where and how it was placed, or even whether it reduced a particular infestation.
A large body of research highlights the vulnerability of both wildlife and humans to commercial over-the-counter ARs. This study supports removal or controlled access of SGARs in routine supermarket, hardware-stores and online sale outlets, reserving them for registered pest-control operators. Purchases should be capped and recorded by buyer, ingredient, quantity, batch and treatment site, with traceability through distributors. Treatments should measure rodent activity before and afterwards, inspect bait uptake, record non-target deaths and remove remaining poison. If treatment fails, the method should change, not simply the amount of poison.
"The South African public and regulators need to know who bought the poison, how much, where it was used and whether it worked," Leighton said. "Without that accountability, we cannot protect public health while preventing avoidable contamination of native wildlife, pets, and even children."
The study describes anticoagulant rodenticides as a "cryptic threat" to wildlife, where these poisons bioaccumulate via complex, multi-tiered processes, with impacts far beyond the intended target species or region. Caracals make this hidden pollution visible, but the red-light warning extends other predators, pets and people across the wider food web.
The paper, Toxic towns: Drivers of anticoagulant rodenticide exposure in an urban edge carnivore, was published in Environmental Pollution and co-authored by Gabriella Leighton, Jacqueline Bishop, Pablo Camarero, Rafael Mateo and Laurel Serieys
