A sign indicating that rat bait has been buried nearby, reading "WARNING: Target: Rats"

Rodenticides Continue to Affect Seattle Wildlife

by Caroline Guzman

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In a recent study, 125 dead raptors, including owls, Cooper’s hawks, and red-tailed hawks, tested positive for rodenticides, according to the latest report from Urban Raptor Conservancy, a Seattle-based organization of avian scientists. However, many other species continue to be exposed to these substances and go underreported. 

The adverse effects of anticoagulant rodenticides (ARs) are well-known. Even though states like Massachusetts, California, and New Jersey have moved away from ARs to more humane pest control, in Washington State, it continues to be legal. 

This unsolved issue has made possible a coalition between Urban Raptor Conservancy (URC), PAWS Wildlife Center, Seattle Audubon, Raptors Are the Solution, Woodland Park Zoo’s Seattle Urban Carnivore Project, and others. 

URC took a leadership role in opening a case study here in Washington State, and it has been testing raptors for several years. Although URC is still waiting for more lab results, Kersti Muul, an independent conservation scientist and urban wildlife first responder, said, “How much data do we need to make a change? Could we start doing something? Because 125 raptors like that’s enough to start.” 

Muul, also a science educator for Seattle Audubon, tells a compelling story of an owl family that she followed for over a decade and found the mother had died due to rodenticides. Muul said, “She (Mom) died in 2019, and her chick from 2019 died in March 2022. So there’s actually two from that family that I knew so well. She didn’t have any external trauma. It looked like she had food stolen from her, because her talons were bloody. So I had her necropsied, and she had three different types of poison in her. I knew that she had been feeding her babies that poison, and her partner. I was devastated about it, because she died for no reason.” It was this incident that led to Muul’s interest in the effects of rodenticides on other species, and led to her joining the coalition.

Urban wild animals of many kinds are ingesting poisoned rats, affecting their nervous systems and cognitive skills, deteriorating their quality of life, and driving them to their deaths. The toxins will also affect their offspring, either via nursing or from parents directly feeding poisoned rats to their young. 

Some common signs of poisoning in wild animals include walking or flying out of balance, repetitively shaking their heads, having an old wound unhealed, and allowing people close to them, which is highly unusual. 

One of the challenges in this ongoing study is that few labs can do this type of testing, and each sample collection costs about $100, according to the URC website. It is expensive and tricky to identify which animal is affected by ARs before they are sent to the lab. 

Nicki Rosenhagen is a wildlife veterinarian at the PAWS Wildlife Center. She has been collaborating on this project for URC by banding live raptors and taking dead ones in for poison testing. “There’s not a way for us to do an easy test on a live bird, because we have to take samples of organs, and we’re not going to do it in live animals. So when we decide to pursue treatment, we can only go based on clinical suspicions, clinical signs, and history,” she said. “We have to wait until we have enough samples to ship, which can take months, and then we need to wait for the lab to do the testing and send the information back.” Not only does this delay valuable information, but there is not enough funding to make this a more effective or faster process. 

Another critical point of discussion is the use of alternative measures to control rats. Some of the alternate solutions that have been discussed are vitamin D overdose (via consumption of cholecalciferol), and bringing the use of snap traps and even rodent birth control to the public’s attention. “Finding an alternative humane solution just as cheap, easy, and effective as ARs right now doesn’t exist,” said Rosenhagen. “We all have to buy into the idea that rodent control doesn’t have to be inhumane, and it doesn’t even have to be lethal. Furthermore, by choosing options that don’t involve poison, we are eliminating the risk of unintentionally harming other animals.” The challenges of finding solutions to these problems are why these organizations joined forces.

Ed Deal monitors raptors for URC, of which he is vice president. He says the two poisons that function as substitutes for ARs are bromethalin (a neurotoxin) and cholecalciferol (vitamin D overdose). These poisons do not build up in the liver as ARs do, “but there is no antidote for bromethalin or cholecalciferol, so if your pet or child eats some, there is no treatment,” Deal said.

For Rosenhagen, the use of vitamin D is “very inhumane and painful for those animals. Again, poison versus poison is not something that I ever recommend.”

Tanea Stephens is the Washington State coordinator and Seattle Chapter director of RATS. They have been working on a pilot case study finding positive results in rodent birth control. “Poison Free by 2023” is a pilot project in Upper Queen Anne that uses a rat birth control solution called ContraPest, and the pilot study has achieved a 91% reduction of the original rat population since the July 2021 deployment. 

The public has the power to make a difference as well. The solution that the PAWS Wildlife Center always offers is “exclusion.” According to Rosenhagen, “exclusion” entails removing bushes near structures where rats feel comfortable hiding and limiting their food sources. She also mentioned other lethal options, like snap traps that are theoretically immediate and won’t pass anything deadly to other animals. 

On April 13, a pair of mountain lion kittens died a few days after being found with three different ARs in their livers, National Park Service officials reported. Rodenticides affecting wildlife is not news. For years, several cases have been recorded about the severity of these toxins in our animals beyond just raptors. Luckily, these organizations continue working in the best interests of Seattle’s urban animals, hoping the public will switch gears to humane pest control.


Caroline Guzman is an animal and wildlife photojournalist based in Seattle, Washington. She covers stories involving animal abuse, animal law, wildlife conservation, and more. Follow her on Instagram @imcarolineguzman and on Twitter @carolineguzman, or contact her via email at imcarolineguzman@gmail.com.

📸 Featured image is attributed to romana klee under a Creative Commons (CC BY-SA 2.0) license.

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