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A Wilder View: How rat poisons impact the entire ecosystem

Rat Poison
Posted at 11:58 AM, Mar 08, 2023
and last updated 2023-03-08 13:58:25-05

MISSOULA - Many of us are familiar with the concept of guests who overstay their welcome. But what if that guest wasn’t welcome in the first place?

The Earth is mainly covered by water, about 71% in fact, leaving only 29% of it to be land. And two-thirds of those lands are now devoted directly to supporting us, either through agriculture, fisheries, urbanization, or infrastructure.

And in the process, many native species have been pushed out. But there's one group of animals that have adapted better than any other. Rodents have been living alongside people since the days of the cavemen.

While they may not be everyone's favorite houseguests, they've become an integral part of our lives. And with that integration comes some bad — like the fact that rodents can carry diseases and destroy our food and property.

In the winter alone rodents invade 21 million U.S. homes which is as much as the population of Florida! So, for years, people have been trying to control them. And that's where chemicals come in.

Chemical biocides called anticoagulants and rodenticides are known to us simply as rat poisons. While they are highly effective, there is a catch. What we don’t always see is that these poisons affect more than rats. Once an animal has ingested a lethal dose of rat poisons, death may not occur for up to 10 days.

So, although you may have applied the poison only in your home, the rat may run outside where it can become an easy snack for a predator. As animals eat rats that have ingested poisons, the poison concentrations increase as it moves up the food chain in a process called bioaccumulation.

These toxins weaken immune systems and can eventually lead to death. One study by the California Fish and Game found high concentrations of rat poisons in bobcats, mountain lions, coyotes, foxes, skunks, hawks, and owls. And 90% of the mountain lions tested and 88% of bobcats that were tested had rat poisons in their system.

These immune systems weakened by rat poisons are also linked to bobcats and mountain lions obtaining mange.

In the wild, the strong survive. But sometimes, even the toughest creatures face unexpected challenges. Meet P-47, a fierce and fearless mountain lion who had survived fires, freeways, and hostile landowners.

But despite all that, the 3-year-old big cat, tracked by California biologists since his kitten days, succumbed to a hidden hazard — an insidious form of food poisoning. Six compounds of rat poisons were found in P-47’s liver and he was also bleeding internally.

He didn’t have to consume rat bait directly to become ill. As apex predators, mountain lions inadvertently absorb toxins through their natural diets, eating poisoned rodents and other predators who feed on them.

But there are other, effective ways to eliminate rats without poisoning animals further up the food chain.

One way is to take away attractants which means picking up trash, shutting and securing garbage lids and not free-feeding pets outside. Live or instant-kill traps can also be used.

Another method is to encourage natural predators. Rodents are the primary choices for birds of prey like owls and people can encourage them to do rodent control by installing nest boxes and perches.

Officials are also making some changes. The U.S. Environmental Protection Agency (EPA) has banned rat poisons with the most toxic and persistent pesticides from consumers, but they are available for commercial use.

They also banned all pellet rat poisons, and they now must be sold as a block or paste bait, packaged with an EPA-approved bait station. The EPA also states, “products marketed to residential consumers may contain no more than 1 pound of rodenticide bait.”

The state of California took it a step further in 2021 by forming a new law banning most uses of rat poisons.

So, the next time you see a rat or a mouse scurrying across the street it may serve as a reminder of the delicate balance we need to strike between controlling pests and protecting our environment.