UPDATE September 2024: Good News! California’s legislature has passed the Poison-Free Wildlife Act, which currently awaits Governor Newsom’s signature.

They’re being called a “modern day DDT”. Like DDT (outlawed in 1972), anticoagulant rodenticides are weapons of destruction. They kill brutally, slowly and indiscriminately, accumulate in fatty tissue, and persist a long time in the environment. Used by homeowners, farmers and exterminators, they are a serious threat to any living being that accidentally ingests them—wildlife, companion animals, and humans (especially children), alike.

Movement through the food chain
Both “second-generation” and “first-generation” anticoagulant rodenticides, the most common rodenticides, were designed to silently block the vitamin K cycle, which is essential for blood clotting. Although the “first-generation” are just as deadly if consumed often, the “second-generation” products have greater potency and build to higher concentrations in rodents, so are more lethal. These “super-toxic” poisons, which have long half-lives, cause rodents to uncontrollably hemorrhage to death—but only if they’re not preyed upon first. Because they’re so slow-acting, rodents may ingest poisons multiple times, which causes residues to accumulate in their bodies to levels many times greater than the minimum lethal dose, which exposes rodent-eating scavengers and predators to large amounts of poison. A poisoned animal can and does lead to indirect secondary (and sometimes tertiary) poisoning of other animals. The recent tragic death of Flaco, the famous Eurasian eagle-owl who was released from his cage at the Central Park Zoo, died in part from poisoning.

Victims do not die quickly; as the poison takes hold, rodents who ingest it continue to move about for days, but more lethargically, so that they become easy prey for dogs, cats, birds, and native mammals like the little raccoon I found on a sidewalk in my neighborhood who apparently had died a slow and excruciatingly painful death by excessive bleeding. Besides other carnivorous or omnivorous mammals such as bobcats, coyotes, foxes, skunks, cougars, bears, and companion animals, these dangerous poisons have spread throughout the food web and inhumanely kill reptiles like snakes and raptors such as owls and hawks—the very animals who can and should be preying on (healthy) rodents. Tertiary poisoning happens when a predator eats another predatory species that’s been poisoned secondarily, such as an owl who eats a poisoned snake who ate a poisoned mouse. And secondary injuries, such as lacerations, can become deadly because victims’ blood has no ability to clot. Even insects, such as bumble bees that often use abandoned rodent nests, can be killed.

Anticoagulants can quickly move through the food chain—in California’s Santa Monica Mountains, the majority of cougars, bobcats and coyotes reportedly have tested positive for exposure and many have died due to poisoning or secondary disease brought on by a weakened immune system. In Africa, raptors are disappearing at a “shocking” rate, partially due to poisons. A 2020 study at Tufts Wildlife Clinic found that 100 percent of hospitalized red-tailed hawks had rodenticides in their livers, and all but one contained brodifacoum, especially deadly to birds. None of the hawks survived.

Another study in 2023 at Tufts revealed the horrors of another rodenticide, a neurotoxin called Bromethalin that can bioaccumulate in raptors. It had already been the cause of severe illness in San Francisco’s Telegraph Hill parrots and “works by interfering with a metabolic process called oxidative phosphorylation, or how an individual cell creates energy. When that process is disrupted, the cells can’t produce the fuel to keep their normal processes functioning correctly, such as regulating fluid balance, or the amount of fluid inside the cell versus outside of the cell. When the cell can’t regulate that fluid balance anymore, it causes accumulation of fluid in abnormal spaces.”

In addition to wildlife, the use of these rodenticides can expose companion animals, such as dogs, who can be poisoned directly when they eat bait from boxes or get into unsecured packaging in their homes. Homeless or feral cats, as well as those allowed to roam and hunt freely also can become poisoned. Victims — no matter the species — suffer horribly, and for many, many days.

Regardless of how any type of rodenticide is distributed — by homeowners, professional exterminators, or HOAs — we, our companion animals, and local wildlife are at risk of exposure. Poisons are no less dangerous when packaged in tamper-proof, sealed bait boxes. The harm they cause far exceeds their limited, alleged benefits.

Room for improvement
Although we’re slowly seeing some positive strides, we still have a long way to go in eradicating these dangerous substances. Late last year, a new U.S. Environmental Protection Agency biological evaluation found that rodenticides harm more than 130 endangered species — including Florida panthers, black-footed ferrets and California condors — and are driving toward extinction at least 73 other species. Because of this, the EPA has proposed new measures to reduce unintentional wildlife poisonings and increase protections for endangered species. However, according to the Center for Biological Diversity, data from past rodenticide restrictions indicates that the new protections fall far short and will continue to leave many wildlife species at risk because, as mentioned above, predators and scavengers consume poisoned animals. Certainly any reduction of harm from these poisons is a good thing, but we need to push for much stricter regulations to ensure that both wildlife and people are safe from them. Learn more at the Center for Biological Diversity.

The good news: There are many things we can do to prevent even the thought of using poisons.
If you do have a serious problem, humane prevention is crucial:

• Learn where rodent are coming in and plug up holes (if you need to put rodents outside, use a live trap).
• Eliminate sources of food, water, shelter.
• Cover or enclose veggie gardens with wire.
• Remove ivy from buildings.
• Clean up/seal up any outdoor food for dogs, chickens, horses, etc.
• Remove bird feeders.
• Clean up/seal up trash. 
• Clean barbecues following use.
• Prevent or remove rodents’ access to fruit and nut trees by trimming branches away from fences, roofs, and other accessible places; attach tree guards on tree trunks to prevent climbers.
• Speak with neighbors who may be contributing to the problem.
• Install rodent birth control, the future of humane, non-toxic coexistence!
• Nurture a native plant garden, to attract natural predators like raptors and snakes.

And just because we see a rat or mouse doesn’t necessarily mean that our yard is infested: In the 22 years I’ve lived in my house, I’ve seen perhaps a couple of mice and four or five rats, all of which arouse my curiosity and interest, not revulsion or contempt. I’ve also noticed a few snakes and many raptors who need such food. Several rats had also been seen this past year at the community garden where I grow food, but raptors in the vicinity apparently did what they do best and there’s been no sign of the rats since. Raptors and other predators are the answer, and there is no such thing as a safe rodenticide. For more information, please visit Raptors Are The Solution (RATS).

© 2024 Eileen M. Stark