High up in a crack willow a white goshawk tore at a mouse it had just snatched from a chicken coop, making the most of its meal.
It was the first white goshawk I had seen all year in the Waterworks Valley where I live and the sighting should have been a cause for celebration. Instead, I was filled with dread in the knowledge that rodents frequenting homes and farms can sometimes carry mice and rat poisons devastating to wildlife.
By coincidence, two days after spotting the goshawk I attended a lecture on rodent control at which it was revealed the more powerful rodenticides were responsible for the widespread poisoning of eagles, hawks, falcons and owls across Tasmania.
The lecture in South Hobart was promoted by Landcare Tasmania and it had as its speaker raptor expert Nick Mooney who said that the right choice of rodent control could mean the difference between life and death for our wildlife.
Birds of prey, including the endangered masked owl, were particularly vulnerable to rodenticides. When they ate dead or dying rodents they were poisoned themselves. Other birds like forest ravens, butcherbirds and even tawny frogmouths were also at risk along with mammals, including quolls and devils.
Mooney, however, said there were ways to minimise the impact beyond using old-stye rat and mice traps. Most rodenticides were based on anticoagulants that killed by promoting uncontrolled internal bleeding. Older types of anticoagulants, called First Generation Anticoagulant Rodenticides (FGARs), required rodents to consume multiple doses, lessening the exposure of wildlife to the poisons. The new Second Generation Anticoagulant Rodenticides (SGARs) were used much more widely, mainly because of the convenience of their “single-dose” effect. They killed rodents more quickly but more residual poison was ingested by raptors or other predators.
Mooney said that when buying rodenticides it was important to look at the labels on the packaging which revealed active ingredients. It was also important to look for the words “single-dose action” which gave a clue to toxicity.
Less toxic (FGAR) poisons contained active ingredients called Warfarin and Coumateraly and the more toxic SGARs, Brodifacoum and Bromadiolone.
“If you are putting down rodenticides a little bit of homework is required to work out what is dangerous,” Mooney said.
The morning after Mooney’s talk I searched for the goshawk again and was happy to find it in the wet forest above my home.
I still have my fears, though, for this pure-white raptor, considered the most beautiful of our birds of prey.
During these Covid-19 pandemic times there appears to have been a drive for self-sufficiency in my neighbourhood, with more and more chook runs being constructed. But I hope the chickens are not attracting a plague of rats and mice, causing property owners to resort to the more powerful one-hit rodenticides to keep them under control.