Walking time bombs’: bird lovers call for ban on poisons
August 12 2020
When word got around the office a boobook owl had been spotted in a nearby inner-city street, everyone in the BirdLife office grabbed their binoculars and headed for the door.
Unsurprisingly, when staff at Australia’s largest bird conservation organisation hear an unusual bird has visited Melbourne’s CBD, they rush to see it (and have binoculars at work).
But there was something wrong with this owl. It sat perched only three metres off the ground, on a tree with no foliage.
“It was completely exposed and close to the ground – you wouldn’t usually see a nocturnal bird displaying that kind of behaviour,” says Birdlife campaigns advisor Andrew Hunter.
Later that day a passerby found it dead under a tree in a nearby park. Hunter, who is also a wildlife rescuer, wanted to get the owl’s body checked for poisoning from anticoagulant rodenticides, or rodent poisons.
So he took it back to the office freezer – used for keeping bird carcasses that will be taxidermied for educational purposes – and arranged for veterinary students at Melbourne University to do a pro bono dissection.
This found large haemorrhages under the skin and in the muscle of the owl’s keel, extending down the length of the left wing and around the carpus (wrist) of the right wing.
The tissues also had very high levels of of the anti-coagulant brodifacoum, enough to cause toxicity and account for the haemorrhages, the dissection report showed.
For Hunter and the other Birdlife staff, it was a first-hand experience of an issue their organisation has been campaigning on for years: the lethal effect of anticoagulant rodenticides, also called second-generation rat poisons, on birds like owls, kites and other birds of prey.
The Australian Pesticides and Veterinary Medicines Authority is currently examining these rodenticides on the basis of concerns for worker exposure, public health and environmental safety.
Birds like boobook owls and black-winged kites can devour multiple rats and mice that have taken bait, says BirdLife Australia’s Sean Dooley. And because the poison takes some time to work, the poisoned rats are like “walking time-bombs”.
It’s a long and painful death for the birds, Dooley says. “These second-generation poisons don’t break down quickly – some can stay in tissues and organs for months, even years.” They can also cause birds to become disorientated, meaning they are more likely to crash into structures and vehicles.
These household products have been banned in some jurisdictions in the US and Europe, but are available from Australian supermarkets and hardware stores. They work by inhibiting Vitamin K in the body and disrupting the normal coagulation process. Poisoned animals suffer from uncontrolled hemorrhaging.
Professional pesticide users would prefer anticoagulant rodenticides were taken off retail shelves and made less accessible to the public, says Eris Hess, associate director of the Australian Environmental Pest Managers Association.
“The real question is why the bird is able to access the rodent. The general public is buying off supermarket shelves and using it incorrectly,” Mr Hess said. Professional users know they should collect the carcasses afterwards, he said.
The association would like a licence required for use, perhaps the safe chemical users licence, which most farmers already have.
All second-generation rodenticides should also be used in bait boxes to contain pests that have ingested poison, so they are not a risk to other animals or children, Mr Hess said.