Laura Erickson's For the Birds

Thursday, December 23, 2021

Rat Poison: Even Worse Than I Thought

Barry the Central Park Barred Owl

Now that my daughter Katie and her family moved to Duluth, even if there weren’t a pandemic, I wouldn’t have a good reason to visit New York, but I felt a little sad that I didn’t get to see Barry, the famous Barred Owl that was first found in Central Park in October 2020 and stuck around to thrill a great many birders. She stayed in Central Park throughout 2021 until August, when she was hit by a maintenance vehicle.   

It seemed odd for a bird who had survived urban life in that very area for almost a year to be killed by something going at a reasonable speed that she must have encountered dozens of times before. Sure enough, a necropsy revealed that her system was loaded with difethialone and lethal levels of bromadiolone, two of the four worst “second generation” rat poisons. Warfarin, a natural product of contaminated, moldy sweet hay, can kill horses and cattle, and was the original rat poison. Because its effects can be reversed with Vitamin K, medical researchers also discovered that it can also be used therapeutically as an anti-coagulant. I’ve been taking warfarin myself since my second heart attack, to prevent clots from ever forming again in a congenital aneurism on my right coronary artery.   

Warfarin is working great for me, but rats have become increasingly resistant, so much more potent second-generation rat poisons are now the rodenticides of choice. We humans are the only species that includes rocket scientists and brain surgeons, but we’re also the only species about which it’s been said, “When you have a hammer, everything looks like a nail.” When faced with a problem, we tend to look for a simple way to smash it, even when smashing leads to more serious problems. According to a great but very disturbing article in the current Audubon, the global market for anticoagulant rodenticides is expected to grow from $3.8 billion in 2020 to $5.8 billion by 2027, with the United States accounting for more than one-third of sales.   

The EPA prohibits companies that register these rat poisons from selling or distributing them “in channels of trade likely to result in retail sale in hardware and home improvement stores, grocery stores, convenience stores, drugstores, club stores, big box stores, and other general retailers.” But Chris Sweeney, writer of the Audubon article, discovered first hand that it was very easy for consumers to purchase large quantities of even the worst of these prohibited pesticides from such places as eBay,,,, and Soon after he did online searches for them, banner ads for these illegal toxins started popping up on his regular browsing sites, such as and Apparently, even EPA regulations isssued in 2008 don’t apply to internet sales. The only state that absolutely bans all of these toxins except for a few specific and critical human health situations is California.  

Rats can take in a lethal dose after a single meal laced with these second-generation rat poisons, but it can take up to five days for them to die, giving plenty of opportunities for predators to find and eat the poisoned and now poisonous rodents. Maureen Murray, director of Tufts Wildlife Clinic, has been studying these chemicals since 2006. In that time, the problem has gotten worse, with more and more birds turning up with multiple second-generation anticoagulants in their system. Chris Sweeney quoted her in the Audubon article, “What makes these particular rodenticides such a concern is the fact that they have these long half-lives…and so they can accumulate in the food chain.”   

The first Bald Eagle found to have died from rodenticides in Massachusetts had three of the four chemicals in its liver. Last year Murray reported that 100 percent of 43 Red-tailed Hawk carcasses she examined had traces of second-generation rodenticides. That followed her 2017 study in which 96 percent of 94 hawks and owls found dead or dying tested positive for the poisons.   

Of course, evidence of exposure does not necessarily translate to cause of death. Sometimes it’s clear a bird died directly from “acute rodenticide toxicosis”: bruising occurs throughout the body, and the lungs can fill with blood. Other complications can include lethargy, immobility, loss of appetite, and small wounds that won’t stop bleeding. While these may not be enough to directly kill a bird or mammal, they do make it harder to survive, as poor Barry the Central Park Barred Owl found out the hard way. And it isn’t just scavengers and predators dying from rat poison. Many of the formulations are sold in small pellet form, easy for songbirds to mistake for seeds. And the baits set here and there in big cities are very attractive to dogs. When Katie and I walked her dog Muxy in her Brooklyn neighborhood, we had to be vigilant every moment, inspecting every single thing she sniffed, even in the dark of night, to ensure that she didn’t pick anything poisoned bait or a small poisoned carcass.  

Our species refuses to clean up our act, so we keep subsidizing rats with our garbage and poorly contained foodstuffs, and we keep poisoning the very creatures that kill rats—Barry the Barred Owls' necropsy revealed a rat in her stomach contents. Even as we decry government regulations, we trust that the EPA will protect us from the worst poisons while letting businesses use every possible loophole to keep making their billions. It’s the American way. 

Barred Owl