An owlet’s first year in 2019. Sadly, this is the Barred Owl that died from secondary poisoning this past March. Image by Kersti Muul

Article by Sharon Wada

Humans have a great capacity for solving problems. But our inventiveness and persistence in addressing an issue sometimes unintentionally create new problems and can harm those that are actually part of the solution.

For local Seattle conservation scientist and Seattle Audubon volunteer Kersti Muul, seeing the collateral damage inflicted by rat poison or rodenticides is personal. She has been monitoring the causes of death for numerous birds of prey in the region including two generations of Barred Owl residents at West Seattle’s Lincoln Park.

In early March 2022, Kersti received a call about a Barred Owl at Lincoln Park that was sitting in a puddle for quite a long time. This could be a natural behavior as owls like to pounce on rodents on the ground and forage on the ground looking for worms. They, like other birds, also use puddles to take baths and drink. But this owl was allowing people to get very close and appeared listless. By the time she reached the location, a bystander had taken the owl to PAWS (Progressive Animal Welfare Society) in Lynnwood.

On exam, the bird was in excellent body condition but with a severe anemia. These findings are often indicative of rodenticide poisoning in an otherwise healthy young adult owl. The veterinary team at PAWS was going to perform a transfusion from another raptor but the owl died before they could start the procedure.

A small yellow bird with a black cap of feathers is perched on a branch

In late 2019, Kersti discovered the carcass of the mother owl in Lincoln Park during a Seattle Audubon bird survey. Image by Kersti Muul

Kersti remembers the mother of this deceased Barred Owl. She had followed her for more than 10 years in Lincoln Park and observed her successfully raise two owlets in 2019. But sadly, later that year Kersti found the dead mother during a Seattle Audubon bird survey. An autopsy showed that she had at least three different anticoagulant rodenticides in her system. So at least two members from one local Barred Owl family may have been impacted by secondary poisoning.

Varied Thrush

Lincoln Park’s Barred Owl mother and owlet together in 2019. This image was captured before the mother died from secondary poisoning. Image by Kersti Muul

“We have to remember that we only observe the problem if we find a sick or dead bird,” Kersti noted. “We can only imagine how many raptors suffer from secondary poisoning in the woods, undiscovered and undiagnosed.”

In Seattle and surrounding communities, we are blessed to have an abundance of different birds of prey living in our parks and pockets of natural habitat. While there may not be enough eagles, hawks, and owls to keep rat populations down in all areas, these predators are nature’s contribution to rodent control. So it’s tragic when they become collateral damage because of our use of rodenticides around our homes and businesses.


An Imported Problem

Young rats pop their heads out of a sidewalk grate in West Seattle. Image by Sharon Wada

Rats, specifically the Norway rats that scurry through our cities, are not indigenous to the United States. They arrived in the US on European ships in the 1700s. The rats stowed away in grain-filled cargo holds and when they disembarked, they found ample habitat in human settlements.

Norway rats thrive alongside people. If there is a food source such as exposed garbage or pet food as well as good hiding places in dilapidated structures or compromised crawlspaces, rats can move in and raise their families.

One of the most natural forms of rodent control are birds of prey. Owls, eagles, hawks and other predators spend their days (and nights) seeking out areas with healthy rodent populations and hunting them. But starting in the early 1900s, rodenticides began to be developed and used in both rural and urban settings. There are two main categories:

  • anticoagulant rodenticides (ARs) which cause the animal to bleed to death internally
  • other poisons such as zinc phosphide and activated vitamin D3 that attack the nerves or internal organs

Much development has gone into ARs over the decades as rats became more resistant to the first-generation versions. In the 1970s, a second generation of anticoagulant rodenticides (SGARs) were produced. These are even more potent and last the longest in rodent tissues, thus posing a higher risk to raptors and other non-target animals. And currently, the pest control industry is developing even more deadly, third-generation anticoagulants. Most of these rodenticides are less accessible to consumers but all are available to commercial pest control companies except in the State of California where certain poisons were banned in 2020.

A Red-Tailed Hawk successfully hunts a vole in a King County park. Hawks, eagles and owls eat rodents including voles, gophers, moles, mice and rats as part of nature’s rodent control strategy. Image by Sharon Wada

Someone who frequently sees the consequences of secondary poisoning in animals is Nicki Rosenhagen DVM, Wildlife Veterinarian at PAWS. She explained that there seems to be a growing awareness of the dangers of SGARs but is concerned that people might choose to replace one poison with another. “All rodenticides are poisons,” she noted. “Once a sick animal is brought into PAWS, an assessment, exam, and blood test can help us to determine a course of action but premortem, it’s usually not possible to definitively determine if a rodenticide is involved. And even if we’re suspicious of poison, we rarely know what specific product we’re dealing with.”

“All of these rodenticides have the potential to cause suffering in the target animal, and they often cause unintentional suffering in other species that prey on the rodents,” she warned. “Depending on which one is ingested, treatment of wildlife or family pets can be long and arduous and sometimes it’s just too late.”

We also have to remember that a poisoned rodent will linger for days and is going to be slower and less alert, thus more easily caught by a hungry predator. And since the poison remains in the rodent’s tissues for months, carcasses will be just as harmful to scavengers like coyotes, corvids or cats. These factors increase the odds that rodenticides will impact non-targeted creatures in our communities.


Building Awareness

So how do we fix this problem?  If we or pest control services continue to use these poisons, what can individuals do?

We need to reexamine our relationship with rats,” Kersti observed. “It’s impossible to eradicate them so we need to be ok with seeing them from time to time. We share a world with rats, moles, and other rodents so poisoning them with rodenticides disrupts that delicate balance from the soil up to the birds and other animals.”

“Do I want them inside my home?” she continued. “Of course not, but there are other humane and successful options for dealing with them. But I’m not going to put poison into our ecosystem just to get rid of a few rats.”

As she spoke, it forced me to reflect on my own stereotypes about rats as disease-carrying, unsightly creatures. We even label them as “vermin.”  Why do we have this fear and instinct to kill rats at all costs, especially when we may be polluting the environment and harming birds, mammals, insects, and even our own pets in the process? Why have we become conditioned to cast a broad lethal net when it comes to rats?

Typical commercial rat poison box. However this one does not display a warning label as it should!  Image by Kersti Muul

Once we put rodenticides into our environment, there is little control of where these substances wind up. “Rat poison boxes are all around us, especially in commercial zones. If the box isn’t properly sealed, dogs, cats, or kids can get into them or the chemicals can leach out into the area,” Kersti explained.

She has documented earthworms eating rodenticide—and worms are a favorite food of owls and other birds. Scientists are also detecting rodenticide in songbirds which are then eaten by Cooper’s Hawks, Merlins, and Peregrine Falcons. And since some of these poisons can be cumulative, birds of prey might be ingesting non-lethal levels over time, eventually reaching a point of toxicity that causes illness or even death.

Some rodenticides are colored (e.g. blue, green, red, yellow) and when they become part of the ecosystem, they can be consumed by various creatures including earthworms which are in turn, food for a variety of birds. Image by Kersti Muul

Finding Solutions

The ripple effect of rodenticides is clear. Fortunately, we have the ability to look for alternative strategies for pest control and make different choices.

Trapping of the animals targets undesired rodents with less impact to other species. A South Seattle homeowners association is switching from traditional rodenticides to deploying “smart’ (e.g. Zapper) traps around their townhouses as part of a pilot project that Kersti is leading. One of their goals is to determine whether or not rats are prevalent and if so, they can adjust the number of traps accordingly. This new approach will avoid harmful impact to the birds of prey that live in the area.

Kersti Muul sets a trap for her pilot project replacing rodenticide with Zapper Traps in a Seattle condo community. Image by Kersti Muul

We can also choose which pest control experts we hire and work with them on poison-free strategies. Wesley Parker, the owner of  Parker Eco Pest Control in Seattle explained her approach. “We avoid using rodenticides and prefer to seal up holes and use physical traps. And one new product that we have tested over the last year is a rat birth control liquid called ContraPest® made by SenesTech. In our commercial test site on the top of Queen Anne hill, we’ve seen a 91% reduction in the resident rat population over 8 months,” she noted. “This product requires patience as it takes weeks for the chemical to stop the rodent’s reproductive cycle but we’re offering this option to conservation-minded homeowners and businesses as it is proven to be very effective with no risk of secondary poisoning.”

Collaboration is one of the keys to building more widespread support for addressing problems that rodenticides introduce into our ecosystem. In order to study the issues further, Seattle Audubon has formed a coalition of local conservation, community development, and government representatives. They will be meeting regularly to share information and evaluate policies that will better protect urban wildlife and habitat.      

Our federal and local governments have a role in this as well. The Environmental Protection Agency is reviewing the above-mentioned rodenticides and was expected to issue guidance in late summer 2022. But city and state governments don’t have to wait. They can also establish policies that restrict the use of harmful poisons and incentivize less- or nontoxic alternatives.

Perhaps most importantly, each of us has the power of choice. When we determine that we need help with pest control, we don’t have to pick our poison. We can avoid them altogether by working with our neighbors to eliminate use of rodenticides and minimize the food and nesting areas that attract rats. In situations where rodent populations require more control, we can deploy traps around our homes and businesses as well as more environmentally responsible products with the assistance of pest control companies that share the same values.

We can also take a fresh look around. Rat and mice prevention may be as simple as not leaving cat food on the back porch or keeping garbage cans out of sight until pickup day. Unfortunately, bird feeders can attract rodents, too. Us bird lovers can do our part by cleaning up spilled seed and placing feeders in a location less accessible to rodents. But ultimately, we have to learn to co-exist with rats and mice on this planet.

The owlet as observed in 2019. Wild barred owls have an average life expectancy of 8-10 years but have been observed well into their teens. This one was barely 3 years old when it died. Image by Kersti Muul

Small changes can have a big impact. Thank you for your interest and efforts towards creating a poison-free environment. Your raptor neighbors will have a better chance of living healthy and longer lives, and provide the community with more years of natural rodent control.

Sharon Wada

Sharon Wada

Board Member

A native Seattleite and graduate of the University of Washington, Sharon enjoyed a decades long career in healthcare information technology, including 25 years managing her own independent consulting firm.  Sharon is an avid photographer but fairly new to birding.  She considers it a privilege to observe and capture images of birds in nature.