A new University of Cape Town study on how rat poison is destroying wildlife has sparked a wave of concern about the scourge that a Nelson Mandela Bay environmentalist has been warning about for two decades.
The publication of the study coincides with International Day for Biological Diversity, which was celebrated on Wednesday last week.
The research, which has attracted international interest and is thought to be the first of its kind, found rat poison in liver and blood samples of caracals, water mongoose, Cape eagle owls, Cape clawless otters, large spotted genets and honey badgers in and around the Mother City.
Dr Laurel Serieys – lead author on the study by the university’s Institute for Communities and Wildlife in Africa, which had just been published in the Netherlands-based journal Science of the Total Environment – said the presence of the poison had been overwhelmingly clear.
“Overall we found 81% exposure across seven species tested. The predators aren’t eating the poisons directly.
“Rather, the poisons are designed to work slowly in the target species, rats, which become sick over a period of days and end up as easy prey for predators,” Serieys said.
In Port Elizabeth, Arnold Slabbert, the founder of wildlife rescue organisation Wildline and the zero-poisons pest control enterprise, Urban Raptor, started raising the issue of secondary poisoning in the late 1990s.
Slabbert’s concern about the lethal effect of rat poison, on owls especially, has been raised in a dozen articles since that time in The Herald and Weekend Post.
Serieys said the species being hit by secondary rat poisoning, which likely included even more species than those sampled, were already facing an array of challenges from increasing habitat loss to vehicle collisions, poachers and fire.
“The study measured the presence and concentration of rat poison compounds in liver and blood samples from 41 animals, with a special focus on caracals as part of the Urban Caracal Project. At 92%, exposure to rat poisons was highest for caracal,” Serieys said.
The caracal project lead supervisor Dr Jaqueline Bishop said they had detected at least one of the four most toxic rat poison compounds – all available in over-the-counter products – in six of the seven species tested.
Caracals living around peri-urban vineyards had the highest exposure to rat poisons.
But the danger zones appeared to be restaurants, hotels and spas on the wine estates plus adjacent residential areas rather than the vineyards themselves, where poisons were not put down by farmers.
The researchers focused their poison testing on caracals but were also able to opportunistically test several other species that had died after being hit by cars, she said.
“The fact that these species use different habitats shows rat poisons may profoundly impact many different species.”
Another collaborator on the study, Dr Nicola Okes, said their findings also revealed how insidious the poison was.“It suggests, in the case of otters, that polluted water run-off from urban areas could transport the poisons into Cape Town’s waterways and the aquatic food chain.“There is mounting evidence globally that rat poisons are a critical threat to wildlife, including threatened and endangered species,” she said.To really understand the problem locally, it had taken support from the public, SANParks and the Cape Town Municipality in the reporting of wildlife killed in road collisions, Okes said.“One of the most significant findings of the study is that exposure occurs at all ages.“Several lactating female caracals were sampled in the study and found to be exposed to rat poisons, suggesting that kittens may be exposed through their mother’s milk.”Bishop said researchers were hoping their findings would stimulate dialogue on how to reduce environmental contamination by rat poisons.“As consumers, we need more eco-friendly alternatives to rat poison and the simplest solution is well within everyone’s reach – improve the management of waste that attracts rats in the first place.”Slabbert said the “quick chemical fix” of poison did not even work, as evidenced by the continuing presence of rats.“One of the problems is that many people are beguiled by the ‘eco-friendly’, ‘raptor-friendly’ labelling of poisons. There is no such thing,” he said.