21
Apr
Study Finds Eagle Populations Experiencing Widespread Rodenticide Exposure
(Beyond Pesticides, April 21, 2021) The vast majority of bald and golden eagles in the United States are contaminated with toxic anticoagulant rodenticides, according to research published in the journal PLOS One earlier this month. Although eagle populations have largely recovered from their lows in the 1960s and 70s, the study is a stark reminder that human activity continues to threaten these iconic species. “Although the exact pathways of exposure remain unclear, eagles are likely exposed through their predatory and scavenging activities,” said study author Mark Ruder, PhD, assistant professor at the University of Georgia to CNN.
Eagle carcasses were retrieved from the University of Georgia’s ongoing Southeastern Cooperative Wildlife Disease Study. Eighteen state wildlife agencies and the U.S. Fish and Wildlife Service all sent in specimens from a period spanning 2014 to 2018. In total, 116 bald eagle and 17 golden eagle carcasses had their livers tested for the presence of anticoagulant rodenticides.
Out of the 116 bald eagles tested, 96, or 83% had were exposed to toxic rodenticides. Forty of the eagles (35%) were exposed to more than one rodenticide compound. Thirteen out of 17 golden eagles were contaminated was rodenticides, with four exposed to a single rodenticide and nine exposed to more than one. The second-generation anticoagulant rodenticide brodifacoum was the most detected compound in sampled eagles. In sum, researchers identified 12 eagles (4%) that had died specifically from toxicosis caused by rodenticide exposure.
The recovery of eagle populations over the last 50 years is a major wildlife success story, showing the power and impact of science, advocacy, and a meaningful regulatory response. DDT and other organochlorines pesticides were eliminated, and the Endangered Species Act was successful at protecting eagles’ critical habitat.
The spot eagles hold at the top of their respective food chains were challenged by human activity, effectively acting as predaceous downward pressure on their population numbers. The current study reveals that similar threats remain that warrant further reforms. Prior studies have deemed anticoagulant rodenticides “super-predators” in ecosystems for the widespread damage that can result from their use. This is because rodents that eat these chemicals, often contained in toxic baits, do not die immediately. The anticoagulant nature of these rodenticides means that they stop an animal’s blood from clotting, resulting in a slow, painful death. The animal becomes confused and slow, blood vessels are ruptured, hair and skin loss begin to occur, and nosebleeds and bleeding gums will present prior to succumbing to the poison.
While a rodent is likely to die from this poison, ingesting it also turns it into a sort of poison trojan horse for any predator that may take advantage of its slow decline. An eagle that eats a poisoned rodent at the edge of death will be the next to succumb to the anticoagulant effects of the chemical. If not killed outright, a poisoning event can weaken a predator’s immune system and make the animal more susceptible to disease. “Humans need to understand that when those compounds get into the environment, they cause horrible damage to many species, including our national symbol, the bald eagle,” Dr. Ruder told CNN.
Over a decade ago EPA issued rules intended to reduce non-target poisonings from rodenticide use. However, the study notes that ongoing poisonings must continue to be investigated. “The prevalence of exposure is concerning, and the documentation of SGAR toxicosis in eagles in this study suggests that exposure and mortality due to SGAR exposure remains a problem in eagles, despite recent risk mitigation efforts,” the authors write.
Fifty years ago, EPA met the challenge of protecting the nation’s iconic birds of prey from collapse. With fair warning of future problems, we need not wait until another crisis to stop the use of toxic pesticides. The state of California is out ahead and has already begun to take action on toxic anticoagulant rodenticides. In September 2020, the legislature voted to ban the use of these chemicals with limited exceptions. Although many advocates rightfully note the need to tighten up the current list of exceptions, the law provides an important first step, and a recognition that this is an issue that can and should be addressed.
It is not just eagles and birds of prey that are threatened by these compounds. Numerous mountain lions throughout California have been poisoned over the last decade, including mountain lion P-22, which, for a time, roamed the Hollywood Hills along Griffith Park’s Hollywood sign. Scientific studies indicate that mountain lion populations in Southern California’s Santa Ana and Santa Monica Mountains are at risk of local extinction within 50 years without intervention.
It is critically important that bobcats, fishers, mountain lions, owls, hawks, and other critically important predators remain at the top of their food chain. Ultimately, it is by embracing and encouraging the growth in their numbers that we can address the excess of pests in human built environments. The installation of owl boxes, for instance, can provide a very effective way to address rodent populations on farms and in large landscaped areas.
Avoid the use of rodenticide baits in and around one’s home. See Beyond Pesticides’ ManageSafe page on least-toxic control of mice for strategies that can be used that do not include the use of highly hazardous baits. And for more information on the dangers rodenticides and other toxic pesticides pose to wildlife, see Beyond Pesticides’ Wildlife program page.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
