A study revealed that birds of prey were found to have traces of rodenticide in their system from eating the anticoagulant rodenticides (AR) used to poison rats and mice at home.

Maureen Murray, the director of Tufts Wildlife Clinic, studied the rodenticide exposure in birds of prey for more than a decade. 

According to Murray, people's use of rodenticide to kill unwanted pests like mice and rats by feeding it poison exposes birds of prey to toxins by eating the mice or other poisoned pets.

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Poisoned Birds of Prey

 Over the past ten years, Murray noticed the increasing number of prey species that come into Tufts Wildlife Clinic have traces of rodenticides in their systems. In some birds, the rodenticides are even at fatal levels.

Murray examined liver and blood samples from 43 dead red-tailed hawks that got admitted to the clinic.

Her test findings showed more surprising results. According to Murray, all or 100 percent of the red-tailed hawks tested positive for anticoagulant rodenticides. In 2017, 97 percent of the hawks tested positive, but the increase to 100 percent is such a "dramatic number."

The lab results suggest that the second generation ARs (SGARs) are found most frequently on the birds.  

According to her, she chose to focus her study on red-tailed hawks because it the most common birds of prey admitted to the clinic, and the particular birds are generalist predators, which provides a measure of how prevalent the poison contamination within the food web. Red-tail hawks not only eat small mammals. Birds, reptiles, or amphibians are also part of its diet, further suggesting that its prey-base is primarily contaminated with poison.

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Impacts of Anticoagulant Rodenticide (AR)

The second-generation ARs are more potent than the first generation ARs in which the rats in Europe have developed an immunity.

AR kills the animals or pests by thinning the blood and causing the animals to bleed to death. SGAR, even if only a single feeding is given, is potent enough to kill a rodent. However, the end does not come immediately. They slowly bleed to death for a few days while continually feeding on the poison. Meanwhile, birds of prey may eat these poisoned animals. Even after the rodent's death, the SGAR residues remain on the carcass, making it lethal for the scavengers. 

Because of its blood-thinning effect, the impacted animals are at risk of bleeding from lacerations and cuts. Since the blood is not clotting, simple cuts and lacerations can be life-threatening as the rodents or its predator will likely bleed to death from the wounds. 

Call for Review of Rodenticide Regulation

Despite the negative impacts of SGARs, it still exists because it is a convenient and effective way to get rid of rats at home, Murray said.

However, there are measures to keep the SGAR use in check. In 2008, the US EPA measured to regulate the sale of SGARs was issued due to evidence of exposure among children, pets, and 'non-target wildlife.'

However, the regulations were not in effect until 2011, which stipulate that only pest control professionals can buy and use the product. However, with the advent of online sales, the effectiveness of the regulation may have been challenged. 

Murray encouraged everyone to consider other approaches in controlling pests other than AR like finding where the mice or rats places, covering mouse holes and cleaning nesting sites, removing their food and water sources. 

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