Rat poison passes through the food chain and threatens carnivores all over the world

Rats thrive around humans, and for good reason: They feed on crops and garbage and adapt easily to many environments, from farms to the world's largest cities. To keep them under control, humans often resort to poisons. But chemicals that kill rats can harm other animals too.

The mostly used poisons are called anticoagulant rodenticides. They work by interfering with blood clotting in animals that eat them. These tempting-tasting bait blocks are placed outside buildings in small black boxes that only rats and mice can enter. However, the poison stays within the rodents' bodies and threatens larger animals that prey on them.

My colleagues and I recently reviewed studies from all over the world with the aim of documenting the exposure of untamed carnivorous mammals to anticoagulant rodenticides. Many of the animals tested in these studies were already dead; others were still alive and a part of other studies.

The researchers found rodenticides in a few third of the animals they examined, including bobcats, foxes and weasels. In a 3rd of the animals, they directly linked the poisons to death – normally by finding the chemicals within the animals' liver tissue.

Most of the poisons discovered in these studies were so-called second-generation anticoagulants, developed since 1970. These products are used exclusively in residential and concrete areas and might kill a rat or mouse after just one night of feedingFirst-generation rodenticides, typically used only on farms, require multiple doses to kill.

These poisons are widespread and their use is basically unregulated in most countries. The use of rodenticides is expected increase and will contribute to the decline of many carnivore species worldwide.

Climbing the food chain

When wild animals ingest rat poison – typically by eating a poisoned rat – the implications can include internal bleeding and lesions, lethargy and a reduced immune response, which may make them more prone to other diseases. In many cases, the animal dies. Sometimes these deaths occur on a scale that Reducing local predator populations.

We began our investigation by compiling a listing of 34 animal species known to be exposed to rat poison. These included members of the weasel and canid families, equivalent to stoats, polecats and red foxes, in addition to wild cats and other carnivores.

Some of those predators, equivalent to mountain lions and grey wolves, don’t normally hunt rodents. Rodenticides have even been detected in semi-aquatic predators equivalent to river otters, which normally eat crustaceans and fish.

It is probably going that enormous carnivores equivalent to wolves devour rat poison by Eating other poisoned carnivores equivalent to raccoons and bobcats.

This movement of poisons along the food chain is named bioaccumulation. The best-known example is bald eagles and other birds of prey. exposed to the pesticide DDT in fish they consumed before the United States banned DDT in 1972. Many affected species, including Bald EagleOsprey and Peregrine Falconshave been drastically reduced for years because of the results of DDT on their populations.

Carnivores at risk

We found dozens of previous studies that attempted to quantify exposure risk, typically by examining the animals' habitats. Some studies found an increased risk of consuming rat poison in urban and agricultural areas, but many also found a high correlation with natural spaces.

For example, a 2012 study found that rodenticides in Fisher marten and marten who frolicked nearby Illegal cannabis cultivation areas in Humboldt County, Californiawhere farmers protected their fields with rat poison.

Other possible aspects for infection were the sex and age of the animal. All in all, further studies are needed to seek out out which animals are in danger.

Most research on this topic is being conducted in North America and Europe. Only a handful of studies have focused on South Africa, New Zealand or Australia, although over half of the world's threatened carnivore species occur in Asia, Africa or South America.

In Africa, for instance, anticoagulant rat poisons could kill species equivalent to the Black-footed catwhich is assessed as endangered. These poisons are also widely used throughout Asia, especially on palm oil plantations. This kind of forested agricultural area is home to many wild species, including carnivores that hunt rodents, equivalent to Palm civet And Leopard cats.

Our study found that 19% of carnivore species on the International Union for Conservation of Nature’s list Red List of Threatened Species have distributions that partially or completely overlap with countries where rat poison exposure in wildlife has been documented. However, rodenticides are listed as a recognized threat in just 2% of Red List species, and none of those are included within the 19% that our review found could also be threatened by rodenticide exposure. This suggests that wildlife researchers and conservationists aren’t fully aware of the reach of those poisons.

Kiawah Bobcats

I’m working on my dissertation on Kiawah Island in South Carolina, where biologists Detection of anticoagulant rodenticides in bobcatsThe island's bobcats have been GPS-collared and monitored for the reason that early 2000s as a part of one in all the world's longest, multi-generational carnivore studies.

In late 2019 and early 2020, three bobcats were found dead from rodenticide poisoning, including two females who died in childbirth. The bobcat population dropped from an estimated 30 to simply 10 individual cats. These deaths attracted media attention and spurred efforts to Limiting the usage of poison on the island and sparked research to know the results of rat poison on bobcats.

Kiawah is a preferred vacation destination, but these bobcats have endured despite a long time of development. Part of my work is attempting to work out how rodenticides and urbanization affect the cats.

In 2020, Kiawah residents volunteered to stop using rodenticides on the island, and the town government conducted educational campaigns explaining the threat to wildlife. Today, there are about 20 bobcats on the island, and work continues to End use of rodenticides.

These poisons have contributed to the death of other charismatic animals, including urban mountain lions in Southern California and Flaco, an eagle owl who escaped from New York's Central Park Zoo and lived within the park for months. In Europe, rodenticides were utilized in the Carcasses of Italian wolves.

Rats damage property, contaminate food and spread disease, making their control a human health concern. However, my research provides further evidence that higher control methods are needed to cut back the necessity for anticoagulant rodenticides.

Community-based efforts like those on Kiawah Island will help. So can urban trash cleanup. But many places all over the world might have higher regulation and oversight of rat poison use.