Rat poison turned up in 78% of Cape Town's dead caracals over ten years

Researchers analysed liver samples from 102 caracal deaths collected in and around Cape Town over ten years, mostly animals killed by cars, and found anticoagulant rodenticides in 78% of the samples analysed, with highly toxic second-generation compounds dominating the exposure profile ^[2][3][7]. The paper, in Environmental Pollution, comes from the Urban Caracal Project at the University of Cape Town's Institute for Communities and Wildlife in Africa with Spanish collaborators at IREC and the Institute of Environmental Assessment and Water Research (CSIC) ^[1][4]. Taken together, that means pest control bought and applied routinely in homes, businesses and on farms is operating as an unmeasured, uncontrolled dosing program on wildlife.

The detail is worse than the headline rate. Most contaminated individuals carried at least three different compounds, and some livers held up to six ^[5]. Older animals carried higher burdens, which the authors read as evidence of repeated, long-term cumulative exposure rather than one-off accidents ^[6]. At 78% of 102 animals, roughly 80 cats tested positive, at an average sampling rate of about ten mortalities a year ^[21][22].

The mechanism explains why this leaks so reliably out of the target species. Anticoagulant rodenticides block the vitamin K cycle in the liver, stopping blood from clotting and causing fatal internal bleeding in rodents and in any non-target mammal or bird that takes a lethal dose ^[8]. Second-generation products, developed in the 1970s partly to defeat resistance to the older poisons, are more potent, can be lethal after a single feed, and persist longer in tissue ^[9][10]. Death is also slow, up to two weeks, so poisoned rodents keep eating and keep accumulating, and arrive in a predator's stomach carrying a concentrated dose ^[11].

For anyone running a site, the risk map is the useful part. The study found hotspots of higher rodenticide counts and concentrations in caracals using vineyards, wetlands, greener urban areas, and areas with more restaurants, cafes and other food outlets ^[16]. That is a list of places where bait is deployed continuously because rodent pressure is continuous.

What the poison does short of killing is the open question. Cats tolerate anticoagulants well and rarely die from exposure outright, and the authors are explicit that sublethal effects in caracals are currently unknown ^[13]. They did find that subadults in poorer body condition carried higher loads ^[14]. The comparison case is the North American bobcat, where exposure has been associated with inflammation, suppressed immune responses and altered gene activity affecting immune defence, skin integrity and toxin processing, correlated with greater disease susceptibility and particularly with fatal mange ^[17]. Other wildlife shows impaired clotting, internal bleeding, poorer condition, lethargy, reduced movement and weakened reflexes, effects that could plausibly make an animal worse at fighting infection, hunting or avoiding traffic, though that chain has not been demonstrated in caracals ^[18]. Senior author Dr Laurel Serieys frames it as quiet attrition: repeated lower exposure "may quietly weaken animals and make it harder for them to cope with disease and other urban dangers" ^[19].

Lead author Dr Gabriella Leighton, now at Stellenbosch University, calls caracals "red warning lights at the top of the food web" because they move between reserves, farms and suburbs and eat a wide range of prey ^[12]. Earlier Urban Caracal Project work found the same poisons in otters, large-spotted genets, mongooses, honey badgers and owls near Cape Town ^[15].

Two things to track. The study could not tie contamination to individual brands, and the practical advice is to read active ingredients and registration numbers, because formulations change and some compounds are being phased out while remaining on shelves ^[20]. Whether any regulator moves faster than the shelf-clearing schedule is the test.