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Got rats? Try these eco-friendly ways to rid your house of rodents

They get the blame for spreading the Black Death through Europe. They can gnaw through cinder block and squeeze through pipes or holes not much wider than a half-dollar. They’re strong swimmers, climbers and burrowers, can survive a five-story fall, and will eat nearly anything. From their twitchy whiskered snout to the tip of their naked tail, some can grow nearly as long as the width of this newspaper page.

They’re rarely seen, because they’re nocturnal. But for North Bay residents, the sound of skittering in the walls at night and gnawed fruit and droppings on the floor in the morning are unmistakable signs that they’ve moved in. Rats!

According to the Marin/Sonoma Mosquito & Vector Control District, who provide free rat inspections and detailed information about evicting them, there’s been a nearly 10 percent increase in public calls about rats this year. Their staff has gone out to make 171 home rat inspections in the last six months, and helped about three times as many distressed residents by phone.

As upsetting as it may be, says Nick Picinich, a rodent specialist at MSMVCD, “Rats are here to stay, everywhere in Sonoma and Marin Counties.”

And, he notes, they don’t discriminate. He’s just as likely to find their trails in new, multimillion-dollar Marin mansions as in old, rural Sonoma County farmhouses. Few pests likely cause as much revulsion and discomfort among homeowners.

But the rats causing problems today are largely a problem of our own making.

First of all, as wildlife specialists are quick to point out, the rats running through our homes and businesses are not native to California. The wild wood rat, a native species, is shy and reclusive, builds nests of twigs and leaves up to 6 feet tall, eats woodland foods and lives out of sight of most people.

The rats that give rats a bad name, the roof rat and the Norway or sewer rat, hitchhiked to the Golden State on canvas-sheeted sailing ships and landed in droves with European voyagers and gold seekers. By 1850 the rat infestation in San Francisco streets, wharfs and hotels was so bad officials were forced to launch an all-out eradication campaign. Which failed.

Today these imported rats are not only widespread, officials at the California Department of Fish and Wildlife acknowledge, there’s actually no chance their populations will ever be controlled. That’s because, in a year, a single female can produce from 4 to 9 litters, with 8 to 12 pups per litter. And each new female can begin bearing in just 90 days.

So why don’t they just stay out in nature? The reason roof and Norway rats move into human spaces, experts like Picinich note, is because humans make the perfect roommates. From the rat’s eye point of view, where there’s people, there’s often a messy abundance of garbage, waste and other wonderful things to eat and lots of cozy places to shelter. So, they gladly follow us wherever we go.

Overflowing dumpsters outside restaurants, unharvested fruit in yards and the rat buffet known as outdoor pet and bird feeders all encourage them to settle in and breed. “Hoarding issues,” Picinich says, from weary experience, “will become rodent issues.” Overgrown yards and woodpiles on the ground, ivy patches and small openings in foundations and rooflines provide perfect entries and nesting spots that are warm, dry and secure from most of their natural predators.

And that’s another reason rats really like human communities. We’ve successfully pushed out most of the wild predators, like foxes, coyotes, bobcats, snakes and owls, who would normally — and happily — regulate the rodent population. Small wonder rats love living with humans.

Disgusted modern home dwellers can employ a wide range of measures to try and rid themselves of the furry visitors. Baited snap traps are widely used.

But one reason rats remain widely successful is that they’re both clever and relatively intelligent, as those who keep them for pets will readily attest. By exploring with an acute sense of both touch and smell, rats quickly learn and memorize the features in their environment. They establish familiar trails through buildings and mark them for easy navigation in the dark. They’re naturally cautious and wary of new things, says Nick Picinich, and will go out of their way to avoid things like traps that suddenly appear.

That’s one reason cities, businesses and homeowners have often turned to poisons to deal with rat infestations. The most common types of rodenticides, introduced in the 1940s, kill by causing internal bleeding and organ failure. In the 1980s, a second generation of such poisons were introduced that worked more slowly, to counter the fact that rats often sample new foods in small amounts over days, learning to avoid poisons that made them ill. But rat poisoning has a mixed record. In 2014 California banned consumer sales of those second-generation poisons, when it became clear they were actually killing a wide range of other animals in the wild.

That’s because the effects of second-generation poisons are often delayed a few days, leaving rats with poison in their body, still mobile, but weakened and disoriented. That makes them more likely to be caught by wild predators or pets. As a result, studies found, the rat poisons were killing owls, eagles, hawks and other hunting birds, as well as foxes, bobcats, mountain lions and other wildlife.

Stella McMillin, a senior scientist in the California Department of Fish and Wildlife’s Pesticides Investigation Laboratory, says that in 2016, tests of dead mountain lions found that 91 percent had an average of two to three different rat poisons in their systems. Despite the 2014 ban, which only permits licensed pest control applicators to use them, those second generation rat poisons are still showing up in similar numbers in other dead predators who hunt rats. Raptors in particular are highly susceptible to rat poisons.

While pest control companies take careful and deliberate measures to limit wildlife exposure, agencies like the MSMVCD and California Department of Pesticide Regulation advise residents to use poisons only as a last resort. In its official guidelines, the DPR notes “rodenticides do not eradicate rodents and may not reduce their numbers for long. If there’s an area-wide population, rodents from the edges move into the available space vacated by the poisoned rodents.”

As an alternative, one Bay Area group is advising communities to stop using rat poisons altogether, and letting natural predators like owls and hawks do their job. Raptors Are The Solution (RATS) was formed in 2011 after resident Lisa Owens-Viani found rat-poisoned young Cooper hawks dead in a neighbor’s swimming pool. The poison’s effect causes intense thirst.

Her group’s co-founder, raptor specialist Allen Fish, notes that one large hawk will eat a rat every day. A barn owl family can eat as many as 3,000 rodents a year. Owens-Viani notes that most people are surprised to learn that hunting birds are actually quite common in residential neighborhoods if they’re allowed to nest, and are protected from human threats. As Stella McMillan with the CDFW notes, just because residents don’t see the raptors, doesn’t mean they aren’t there.

Fish, who heads the Golden Gate Raptor Observatory, confirms that Sonoma County is home to many rat-hunting bird species, including Red-shouldered and Red-tailed Hawks, Golden Eagles, Cooper’s Hawks, Barn and Spotted Owls.

RATS distributes information and public advertising to try and encourage California residents to avoid rat poisons and instead support the natural hunters. Supported by small donations and grants, they also provide owl nesting boxes, once it’s confirmed that no one in the neighborhood is using rat poison. One advantage of raptors in the neighborhood is that they tend to have larger broods when food is plentiful, meaning they automatically keep up with exploding rat populations.

But all parties note that relying on wildlife or other means to control house rats isn’t the most effective solution. The first and most effective strategy for homeowners is to exclude rats from the house and yard in the first place. Rats are attracted to garbage, compost heaps, woodpiles, and fallen fruit and small entry holes that homeowners have left uncovered around the house. Rats also attract other rats. Picinich recommends contacting his agency for information, or reviewing the guidelines and tips for keeping rats away posted on their website, msmosquito.com/programs-services/rodent-program.

Nizza Sequeira of the MSMVCD also notes that roof and Norway rats carry diseases that can be spread to humans, and measures should be taken to sanitize the home if they’re found. Snap traps and electrocution traps are effective at catching rats in the house and garage, and several local companies also offer poison-free services. Catching rats and releasing them alive somewhere else is actually against State law. Rats are known to devastate bird nests and disrupt wild habitats, or spread disease.

Ultimately, the patter of rats’ feet in the rafters is a reminder that, despite appearances, we’re living in and are surrounded by nature.

Stephen Nett is a Bodega Bay-based Certified California Naturalist, writer and speaker. Contact him at snett@californiasparks.com.