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Resident sees dangers of rat poison to urban wildlife first-hand

barn owlW

Davis resident Cayce Wallace found this barn owl dead under a tree in her front yard on Oct. 19. Lab tess confirmed that the owl died of brodifacoum, a toxic ingredient in D-con bait poison for rodents. Courtesy photo

By
From page A1 | November 21, 2013 |

Davis resident Cayce Wallace has transformed her back yard into a wildlife sanctuary.

Thickets line the sides of her home. Squirrels nibble at ears of corn carefully laid about the ground. Even a small pond dug into the earth offers the urban animals who come and go a water source.

It’s easy to imagine, then, Wallace’s dismay last month when she and her dog stepped outside to find a barn owl lying motionless in the grass in her front yard.

The owl had died.

“She was still soft and warm,” Wallace said. “Her eyes were still glassy and open. It was just devastating. I could not believe it.”

What also struck her, however, was aside from blood that had collected around its beak, the barn owl, who with several younger birds often roosted in a hackberry tree in front of her home, had no other apparent injuries.

As Wallace later would learn from a toxicology report performed by the Department of Fish and Wildlife’s Wildlife Investigations Lab, the owl had died from a toxic dose of brodifacoum, a compound commonly found in rodenticides, or rodent poison.

The compound, a second-generation anticoagulant rodenticide (SGAR), seems to be a serious problem for urban wildlife.

According to Dr. Robert Poppenga, senior toxicologist and the head of the toxicology section of the California Animal Health and Food Safety lab at UC Davis, the poison that killed the owl likely came from a rodent it had eaten that had consumed the bait, but had not yet died.

While local wildlife biologists and researchers don’t have data about how often these lethal secondary poisonings occur, it’s becoming almost undisputed that bait poisons containing SGARs cause great harm to more than just rats and mice, the intended targets.
“Wherever the anticoagulated rodenticides are used, particularly the longer-acting second-generation ones, there’s no doubt that a lot of different, what we would call non-target species — species like dogs or owls or bobcats — do become exposed,” Poppenga said.

“And it can contribute to the demise of those individual animals.”

Poppenga also said that while it’s not always the case that the owl dies from the substance, an extremely high percentage of the raptors tested after they have died carry at least some of the compound in their system.

“Rodents survive for several days after consuming a lethal dose of SGARs and often will continue feeding on the bait,” say researchers in an article published recently in Environment International about the effects of the compound on birds in Canada

“Poisoned animals may remain active and available for capture by predators for some period after ingestion of the rodenticide.”

The research also points out that the poison slows rodents down enough to where they linger longer in open areas, exposing them to higher levels of predation.

Meanwhile, it’s not only predators of rodents who are affected by these rodenticides.
Dogs often can access the bait boxes that are placed near garbage cans and Dumpsters to target rodents, and they are susceptible to the effects as well.

Late last year, veterinarians at the UC Davis William R. Pritchard Veterinary Medical Teaching Hospital warned dog owners about bait boxes and SGARs, as they had seen a spike in accidental rodenticide poisonings, which can turn fatal if untreated.

Wallace, a dog trainer, says she constantly sees and hears about dogs who have gotten sick or even have died because of the poison.

“Many of them are not making it,” she said this week.

While organizations like the EPA are working to strip products such as d-CON off of retailers’ shelves, the products can still be purchased locally.

After the problem with rodenticides literally dropped right into her lap, Wallace wants to make sure folks in town are aware of dangers.

“We have this very delicate web of urban wildlife and unfortunately we’re messing with it,” Wallace said. “People don’t know the dangers of pesticides.”

On Tuesday, Wallace presented a resolution to the City Council that she hopes the city’s leaders will adopt.

The resolution urges local businesses to stop selling these dangerous rat poisons and encourages residents to stop purchasing the products.

John McNerney, the city’s wildlife resources specialist, says residents who are concerned about rodents are advised to seek alternative control methods, especially considering the known repercussions to non-target species.

McNerney recommends mechanical traps, such as snap-traps or a product called Rat Zapper, a box that has a capacitor that electrocutes the rats when they enter the apparatus.

Rat complaints come from people who have fruit trees, compost piles and vegetation, McNerney said. Cleaning up the fruit as it falls will help reduce the rats’ presence.

The city also has spearheaded two separate barn owl box programs over the past few decades to encourage more predators to roost in urban areas and subsequently help control the rodent population. The boxes provide nesting space for the owls, and when carefully located, the owls that nest there can have success in controlling rodents in a much more environmentally safe way.

McNerney says the city also has asked hardware stores in town to participate in a program called “Our Water-Our World” that spreads awareness about less toxic chemicals.

“(These poisons) pose such an unnecessary risk for our wildlife,” Wallace said. “It’s important for people to know we could cause a lot of accidental deaths.”

— Reach Tom Sakash at tsakash@davisenterprise.net or 530-747-8057. Follow him on Twitter at @TomSakash

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Tom Sakash

Tom Sakash covers the city beat for The Davis Enterprise. Reach him at tsakash@davisenterprise.net, (530) 747-8057 or @TomSakash.
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