Sarah loves listening to the forest in her block of bush near Bateman’s Bay, New South Wales, slowly coming back to life after the disastrous fires of 2019.
“I can hear a mighty owl here, which is amazing,” she says.
“And also a barking owl.”
When Sarah struggled with the mouse plague earlier this year, she knew that what she did could have consequences.
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Her neighbors baited the mice with rodenticides, but Sarah had heard that some chemicals could accidentally poison wildlife, including owls that would eat mice or rats.
“I found a dead rat in the garden and was very worried,” she says.
She decided to increase her use of live mousetraps, but encountered a catch.
“I bought a few more mousetraps at Bunnings and all the shelves were empty – everything that had to do with mice.”
In between COVID-induced runs on toilet paper, there was a mouse plague run on traps – and rat poison.
At the height of the mouse plague, rat traps and rat poison flew off the shelves.
Delivered: Lisa Herbert
)
The most popular household rat poisons in Australia contain a potent group of pesticides called second generation anticoagulant rodenticides (SGARs).
These include chemicals like Brodifacoum, Difenacoum and Bromadiolone, which the NSW Agriculture Minister wanted to “napalm” the state’s mouse plague earlier this year.
SGARs cause internal bleeding and build up in the body, including the liver.
They’re effective because they’re slow to act, says Michael Lohr, zoologist and research fellow at Edith Cowan University.
“As soon as mice eat They don’t get sick right away, so they’re happy to come back and eat more, and during that time they can build up a lot more of this poison in their bodies. “
While such plagues are devastating to farmers, the national pesticide agency, the Australian Pesticides and Veterinary Medicines Authority (APVMA), foiled the plan.
The agency cited the “risk of secondary poisoning to non-target species, including birds, fish and reptiles,” as well as the toxicity of the chemical to humans who might eat certain animals from treated areas. Even grain farmers agreed that there are safer options.
But while many breathed a sigh of relief that bromadiolone was not approved for widespread agricultural use, the public can still buy such chemicals in supermarkets and hardware stores for use near homes and other buildings.
And there is growing concern that this is poisoning the environment and killing wildlife, including owls that eat rodents.
Rodents can be a tasty snack for owls, but if they have eaten long-lasting rat poison they can be “poisonous time bombs.”
ABC New England Northwest: Donal Sheil
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For owls that feed on rodents, rats or mice poisoned by SGARs are a real threat.
“They are basically poisonous little time bombs,” says Dr. Lohr, who carried out some of the scant research on the effects of rodenticides on birds.
He previously found evidence that these chemicals poison boobooks, the smallest and most widespread owl in Australia.
Boobooks are little owls and prefer mice over rats. (
Delivered: Simon Cherriman
)
Researchers in cities like Sydney also fear that these household rat poisons are affecting mighty owls.
Holly Parsons of Birdlife Australia says vomit pellets from mighty owls in Sydney show they are eating more rats.
“We found that diet has changed over the past few years,” she says.
“Especially the inner-city birds … they take fewer possums and more rodents.”
Your organization is currently working with Edith Cowan University to analyze liver samples collected from mighty owls found dead in Sydney. Many of the owls had internal bleeding.
In addition to possums (as seen here), mighty owls eat rats. (
Delivered: Richard Jackson
)
For Dr. Lohr is bleeding like a smoking gun.
“At this point it looks suspicious.
“It’s one of the physical signs you’d expect to see with the anticoagulant rodenticide.”
Dr. Parsons says while mighty owls appear to breed well in urban spaces, many of them die.
“We lose about 13 to 15 percent of the population in Sydney every year – adults and chicks.
“We have very strong suspicions that some fatal rodenticide poisoning has occurred in these birds.”
Evidence in vomit pellets from mighty owls shows that some are now eating more rodents. (
Delivered: Nick Bradsworth
)
Aside from reports of rodenticide poisoning in wildlife, there is also evidence that SGARs are building up in the food chain. A study from Tasmania found SGARs are found in wedge-tailed eagles that don’t even feed on rodents.
A public consultation conducted by APVMA last year found that many people wanted stronger restrictions on such rodenticides.
The APVMA said in a statement it was “is currently reviewing appropriate regulatory options to address concerns “but did not offer a timeframe for this process.
“We are still urging APVMA to take these products off public sale,” says Dr. Parsons.
According to Dr. Lohr, Australia should follow the example of countries like the United States in restricting the use of these chemicals to licensed pest controllers.
“In Australia, the general public is allowed to buy as much as they want.”
The threat of rat poison increases the existing burden on owls
Globally, many birds of prey such as owls are threatened, but while many owl researchers are concerned about the emerging problem of rodenticide poisoning, perhaps the greatest risk for owls is habitat loss.
Ornithologist Stephen Debus, an associate professor at the University of New England, says bushfires and agriculture are the main culprits.
Bushfire has destroyed much of the owl habitat. (
Delivered: Simon Cherriman
)
Urbanization, especially on the coast, is also destroying the owl habitat, says Dr. Debus.
And the deterioration in inland waterways also affects the owls that live there – that means less prey and fewer tall old trees like redgums, which provide important nesting holes
Owls are also killed by cars, killed on power lines, and trapped in barbed wire fences.
“You can’t see them at night,” says Dr. Debus.
Dr. Debus knows of an owl that was found in barbed wire. It was taken to game keepers but died.
Foxes and cats also kill owls, he says, with cats also killing owls by transmitting the disease toxoplasmosis to them.
A rescued barn owl in a temporary home with a wildlife keeper. (
Delivered: Wildlife Victoria
)
How do we know how many troubles owls are in?
Dr. Debus says while studies show some species of owls are in decline, we don’t really know how many problems owls are having.
And that has an impact on whether you can legally protect them.
“To get something listed today, you need pretty robust data to show that it has some decline over a period of time,” says Dr. Debus.
Unfortunately, this barking owl did not survive the injuries it suffered from getting caught in the barbed wire. (
Delivered: David Wright
)
A challenge in collecting data on the population of owls is the fact that they are active and difficult to count at night. For this reason, scientists use sound recordings of their calls to track the whereabouts of the birds.
You can help scientists with this quest by becoming a citizen scientist in the ABC’s interactive Hoot Detective.
While some places in NSW are still suffering from the mouse plague, Sarah enjoys a little respite on the south coast in the cooler weather.
But she worries that the mouse numbers could explode again in the spring.
“They’re damaging the roof, they’re eating up the electrical wiring, so all you have to do is stop them,” she says.
The next time she experiences Mouse Armageddon, she’ll try to make bulk mouse traps out of plastic, pop-up containers filled with water.
“You put peanut butter on the garbage can lid and when the mice head towards the delicious peanut treat, they slide off the lid and drown en masse in the water.
At least the owls will thank her.
And if that doesn’t work, she can always try other options suggested by Birdlife Australia for owl-friendly methods of dealing with rodents.
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