Towards compassionate coexistence with rodents, rat poison is not the solution

OPINION – My Washington DC apartment had many rat neighbors.

The alleyway where all the neighborhood trash was collected had open lid trash receptacles and was poorly maintained. It was unsurprising, at least to me, there would be occasional rat sightings. When my neighbors started complaining, I suggested we clean up the alleyway.

Instead, they called a pest control company to put out rat poison. It’s a story that’s all too common.

The pest control industry wants to stay this way, pushing back against any legislation that restricts rat poison. That’s what’s happening in California as lawmakers consider the Poison Free Wildlife Act, or Assembly Bill 2552, to expand existing restrictions on toxic rat poisons that are harming and killing unintended wildlife.

Rats are a human commensal species, benefiting from the resources humans unintentionally provide. To reduce the rodent population in the apartment alleyway, the onus should have been on us to remove the attractants. That’s why I took down my bird feeder, removed all the ivy sprawled across the ground, and ordered garbage bins with lids.

But before I could find out if my plan worked, the rat poison had taken its toll, leaving dead or dying rats everywhere. It was distressing. I began researching the impacts of rat poisons and learned about the ecosystem wide consequences these poisons were having on wildlife.

A nation-wide study found that over 83% of bald eagles tested positive for anticoagulants, a class of rat poison. Through secondary exposure, animals that prey on poisoned rats, also ingest poison. This has led to wide-spread exposure throughout the food-web, where rat poisons have been found in mountain lions, foxes, hawks, owls, and even otters – to name a few.

I now live and work in Davis as a postdoctoral scientist, investigating the impacts of rat poisons on non-target species, such as the gray fox. Since 2020, California has passed two bills that restrict the use of some of the most dangerous rat poisons, second-generation anticoagulants and the first-generation anticoagulant, diphacinone. Despite these restrictions, evidence shows wildlife are still needlessly harmed or killed.

In a 2022 report from the California Department of Fish and Wildlife, over 92% of gray foxes, and over 87% of threatened San Joaquin kit foxes continued to test positive for anticoagulants. The latest legislation, AB 2552, is scheduled for a vote later this month and will add the remaining first-generation anticoagulants to existing restrictions. This bill is sorely needed to prevent further wildlife poisoning.

I strongly believe that rat poison is not the answer to managing rodent populations, and the science agrees.

Rat poison offers only a temporary reduction to a large population management challenge. A more sophisticated and humane way to manage the population is rodent fertility control. A single breeding pair of rats can produce over 1,250 descendants in one year, such that populations inevitably rebound after poison applications, and rapidly. A pilot study in Washington DC using rodent fertility control showed rat populations were reduced by over 90%.

Contrary to popular belief, rodents do not carry more parasites than other animals. It is worth noting however, that rats exposed to anticoagulants have significantly higher loads of Leptospira spp. infections – which can spillover to humans operating antagonistically against public health.

Poisons have failed to eradicate rats, despite being implemented for centuries. Having a significantly reduced, sterilized, population of healthy rats is the most harmonious and attainable rodent management solution. This can be achieved by combining fertility control with improved sanitation and rodent-exclusion practices, and perhaps the acceptance that some rats, will always be, coexisting alongside humans.

Rebecca Gooley (she/her) is a David H. Smith Conservation Research Fellow based at the University of California, Davis.