The Rats thrive around humans for good reason: it is They feed on crops and garbage and it is easily adapt to many environments, from farms to the largest cities in the world. To control them, people often resort to poisons. But the chemicals that kill rats They can also harm others animals.
The poisons most used They are the anticoagulant rodenticides. They act interfering with coagulation from the blood of the animals that consume them, which They bleed to death. These tempting-tasting bait blocks are placed outside buildings, in small black boxes that only rats and mice can enter. But The poison remains in the body of the rodentsthreatening larger animals that feed on them.
Recently, my colleagues and I We review studies from around the world who were trying to document the Exposure of wild mammalian carnivores to anticoagulant rodenticides. Researchers detected rodenticides in about a third of the animals in these analyses, including wild cats, foxes and weasels. And They directly linked poisons to the deaths of one-third of the animals that died.
The use of rodenticides is not regulated
Most of the poisons detected in these studies were the so-called second-generation anticoagulant rodenticides, developed from 1970 onwards. These products are They are used exclusively in residential and urban areas and can kill a rat or a mouse after feeding on them for just one nightFirst-generation rodenticides, typically used only on farms, require several doses to kill.
These poisons They are widely available and their use is not regulated. in most countries. Although it may be contributing to the decline of many carnivore species around the world, it is Its use is expected to increase even more.
VIDEO | Flaco, a Eurasian eagle owl, escaped from New York’s Central Park Zoo in 2023 and lived in the park for over a year. Rat poisons in his system may have contributed to his death in 2024.
Moving up the food chains
When the Wild animals consume rat poison –usually by eating a poisoned rat– Effects may include bleeding and internal injuries., lethargy and one reduced immune responsewhich can make them more susceptible to other diseases. In many cases, the animal dies. Sometimes these deaths occur on scales large enough to reduce local predator populations.
We begin our review by compiling a list of 34 species known to be exposed to rat poisonsAmong them were members of the families of the weasels and the dogsas stoats, western polecats and red foxesin addition to wild cats and other carnivores.
Surprisingly, some predators exposed to the venom, such as pumas and the gray wolves, They do not usually hunt rodentsRodenticides have even been detected in semi-aquatic predators such as the river otterwhich normally feeds on crustaceans and fish.
It is likely that large carnivores such as wolves are consuming rat poison to the feed on other poisoned carnivoressuch as raccoons and lynxes.
IMAGE: Among carnivores studied post-mortem by the U.S. National Park Service, the vast majority have tested positive for exposure to rat poison. Santa Monica Mountains National Recreation Area.
This movement of poisons in the food chain is called bioaccumulation. In the best-known example, important raptors were exposed to the pesticide DDT in the fish they consumed before the United States banned it in 1972. Many species affected, including bald eagles, ospreys and peregrine falconsthey saw rdrastically reduce its population for years due to the effects of DDT.
Carnivores in danger
We found dozens of previous studies that attempted to quantify the risk of exposure to rat poisonsusually by examining the animals’ habitats. Some studies have found an elevated risk of consuming rodenticides in urban and agricultural areas, but also in natural spaces.
For example, a 2012 study found rodenticides in martens –medium-sized carnivores– that frequented illegal cannabis cultivation sites in Humboldt County, Californiain which They used rat poison.
Other factors that may contribute to exposure include the sex and age of the animal. In short, further study is needed. What animals are in danger?.
Little attention to Africa, Asia and Australia
Most of the research on this topic is carried out in North America and EuropeTo date, only a handful of studies have focused on South Africa, New Zealand and Australia, although more than half of all carnivore species of global interest They are found in Asia, Africa and South America.
In Africafor example, anticoagulant rat poisons could threaten species such as the black-footed catclassified as vulnerable. These poisons are also widely used in Asiaespecially in palm oil plantations. Many wild species live in these types of forested agricultural areas, including carnivores that hunt rodents, such as the common palm civet and the leopard cat.
Our study revealed that 19% of carnivore species included in the Red List of Threatened Species of the International Union for Conservation of Nature have distribution areas that overlap wholly or partially with countries where wildlife exposure to rat poison has been documented. However, Only in 2% of cases does the Red List list rodenticides as a recognized threatand no species are included in the 19% that our review indicates may be threatened by rodenticide exposure. This suggests that wildlife researchers and conservationists They are not fully aware of the scope of these poisons.
The Kiawah Lynx
I am doing my PhD on Kiawah Island in South Carolina, where biologists have detected anticoagulant rodenticides in lynxesThese island felines have GPS-enabled collars and have been monitored since the early 2000s, in one of the Longest multigenerational studies of a carnivore in the world.
IMAGE: Researchers studying Kiawah’s bobcats take measurements and blood samples, check for parasites, and fit microchips and GPS collars. All animals are handled with proper permits. Meghan P. Keating/Clemson University, CC BY-ND.
Between late 2019 and early 2020, they were found Three lynxes killed by rodenticide poisoningincluding Two females who died while giving birth. Its population was reduced from an estimated 30 to just 10 individuals. These deaths attracted media attention, spurring efforts to reduce the use of poisons on the island and launched research to understand how rat poisons were affecting lynxes.
Kiawah is a popular tourist destinationbut these lynxes have persisted through decades of urban development. Part of my work tries to unravel how rat poison and urbanization are affecting them.
In 2020, Kiawah residents They volunteered to stop using rodenticides on the islandand the municipal government carried out public education campaigns explaining the threat it posed to wildlife. There are currently about 20 lynxes on the island, and work is ongoing to put an end to the use of rodenticides once and for all.
These poisons have contributed to the death of other charismatic animalslike the urban pumasin Southern California, or Flaco, a Eurasian eagle owl who escaped from New York’s Central Park Zoo and lived for months in the park. Europerodenticides have been found in the Italian wolf carcasses.
IMAGE: Urban clean-up campaigns like this one in London can help control rat populations. Mark Kerrison/In Pictures via Getty Images.
The Rats damage property, contaminate food and spread diseasehence Controlling them is a human health problemHowever, my research adds to the evidence that need better methods control to reduce the need for anticoagulant rodenticides.
Community efforts like those on Kiawah Island can help. So can cleaning up garbage in cities. But it is likely that in In many places around the world, better regulation and monitoring of rodenticide use is needed.
Meghan P. KeatingPhD Candidate in Wildlife and Fisheries Biology, Clemson University.
This article was originally published in The Conversation. Read the original.
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