In a sample of eagles from across the US, rat poison was found in about 80 per cent of the birds. This widespread exposure to toxic chemicals could impair their health or even lead to death.
“This really suggests that despite the best efforts to use these compounds wisely and minimise the opportunity for the raptor species to be exposed, they’re still somehow getting exposed,” says Mark Ruder at the University of Georgia.
Between 2014 and 2018, Ruder and his team determined the cause of death for 303 golden eagles (Aquila chrysaetos) and bald eagles (Haliaeetus leucocephalus), which were sent to them from around the US. Some deaths couldn’t be explained, but the team determined that 4 per cent of the eagles died directly as a result of rat poison.
They tested 133 of the birds for anticoagulant rodenticide, the most common rodenticide, which can also target opossums and beavers, and found that 82 per cent of the birds had it in their body.
There was a high prevalence of what are known as second-generation anticoagulant rodenticides, which are highly toxic and can remain active for months after ingestion. These have been tightly regulated by the US Environmental Protection Agency since 2011 and are only available for commercial use.
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Eagles often scavenge, and rodents killed by the poison could become their food, although it still isn’t clear how exactly the eagles came into contact with it. It is also unclear whether the poison can affect reproduction or impair their health in other ways, says Ruder.
“Such widespread exposure indicates that this issue is more than a localised phenomenon, and if there are widespread health impacts they may occur throughout the population,” says Garth Herring at the US Geological Survey, who wasn’t involved in the study.
The findings are “alarming”, Ruder says, particularly because eagles and other raptors have recently rebounded from the brink of extinction caused by another toxic pesticide, DDT, which caused the birds to produce thin-shelled eggs. The threat of rodenticide may be exacerbated when combined with lead and bromide poisoning, which has also been documented in eagles.
“There is clearly widespread exposure of bald and golden eagles to these compounds, and whether it was directly causal in their death or not, the high prevalence that we found speaks to the potential,” he says.
Journal reference: PLoS One, DOI: 10.1371/journal.pone.0246134