Common product banned around the world is killing our owls

Professor Raylene Cooke opens her freezer and gently removes a stiff powerful owl wrapped in plastic.

She will later defrost the mighty predator and send its liver away for pathology testing, but Cooke’s almost certain how the owl died: rat poison.

Powerful owls eat as many as 250 possums a year.Credit: John White

Powerful owls predate on possums, snatching as many as 250 a year in their lengthy talons. But those possums are increasingly falling prey to another predator.

Whenever he goes into Bunnings, Associate Professor John White from Deakin University’s school of environmental sciences shudders at what he calls the “wall of death” – shelves of rat and mouse poisons such as RATSAK and The Big Cheese.

Most of the products on sale in Australia at Bunnings, Woolworths and Coles are second-generation anticoagulant rodenticides, known as SGARs. They prevent animals’ blood from clotting and cause them to bleed out internally.

They are effective at killing rodents and legal for sale in Australia, but their effect has spread far beyond their intended market.

Professors John White and Raylene Cooke examine two owls they believe were poisoned.Credit: Eddie Jim

Banned in the United States, Canada and the European Union, second-generation rodenticides are killing our native wildlife at an alarming rate.

“We think this is one of the biggest international issues of our time for poisons in the environment,” said White.

“It’s the DDT of our generation. We shouldn’t be allowed to even buy the rat poisons we can buy in Australia – in Europe and North America, they’re banning them.”

During 2020 lockdowns, people started bringing Cooke – who specialises in Australian owls and raptors – dead owls at the rate of one a week.

The talons of a powerful owl, found dead in Victoria.Credit: Eddie Jim

In 2022, a team of scientists at Deakin University, including Cooke and White, dissected 160 possums and sent samples to the National Measurement Institute to see what was killing the animals the powerful owls predated upon.

They found rat poison in 91 per cent of brushtail possums tested and 40 per cent of ringtail possums tested.

SGAR poisons are so toxic that they survive even after an animal is killed and can kill birds or animals that eat the dead rodent or possum. The poison can also be in live possums eaten by owls.

Powerful owls eat as many as 250 possums a year, but are increasingly being killed by their diet.Credit: John White

Cooke and White are among six co-authors of an alarming new study based on that work that proves SGARs have entered the foodchain of apex predators such as powerful owls and barn owls via possums and rodents.

Further testing revealed SGARs in powerful owls and wedge-tailed eagles, neither of which primarily consume rodents.

The ratios of SGARs found in powerful owls was similar to the levels detected in possums.

Apart from the powerful owl, Cooke’s freezer holds a boobook, a barn owl and a tawny frogmouth – all of which were discovered dead in Melbourne and regional Victoria, having eaten possums or rodents that had consumed SGARs.

Clockwise from top left: a boobook, a barn owl, a powerful owl and a tawny frogmouth. All are believed to have been poisoned by rat bait.Credit: Eddie Jim

“We’re finding that poison in agricultural areas, but we’re finding it in urban areas as well,” Cooke said.

“This is not just an agricultural issue, this is increasingly becoming an urban issue.”

She said brushtail possums – which eat a more varied diet – appeared to be consuming more rat poison, probably in roof cavities and scattered around homes, than ringtail possums.

“Australia is so far behind, and we are urging the APVMA to shift all anticoagulant rodenticides onto the restricted chemical products list, which would take them off the shelves of our supermarkets and hardwares.”

A spokesman for the Australian Pesticides and Veterinary Medicines Authority (APVMA) said the regulatory body “takes all concerns related to safety of humans or non-target species very seriously”.

“The APVMA is also aware of decisions taken by comparable regulators, such as limitation of use of second-generation anticoagulant rodenticides in North America, where they are available to commercial pest controllers and for agricultural use, including uses in bait stations, baiting in burrows and baiting in and around buildings,” he said.

“Based on concerns identified through the published literature and through a public consultation, the APVMA initiated a reconsideration of both first- and second-generation anticoagulant rodenticides.”

A scientific assessment was “well advanced”, he said, and a regulatory decision would be published before the end of the year.

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