The annual battle against rats and mice invading gardens and homes in winter has had a tragic side-effect – birds of prey have been killed by rat poison.
The damage that rodenticides are causing to our owl populations, specifically, was highlighted in an ABC news report last month but the problem has been ongoing for a number of years.
When wildlife biologist Nick Mooney first raised the issue locally about a decade ago I did a quick survey of the raptors in the Waterworks Valley in the southern reaches of Hobart. I noticed that the once common brown goshawk and collared sparrowhawk had dropped off in number but I could still hear the raucous call of the masked owls coming from the wet forest above my home. I ascribed the drop-off in goshawk numbers at the time to a boom in hobby farms, particularly chicken runs and their propensity to attract rodents, which in turn prompted property owners to seek powerful poisons to rid themselves of the problem.
Happy, I had noticed that birds of prey had returned in the past year, so it was with shock that I viewed the report about the poisoning of masked owls on the main ABC evening news. The news report featured an interview with Craig Webb of the Tasmanian Raptor and Wildlife Refuge at Kettering, who outlined the scale of the devastation on a species that is under threat in Tasmania, more so than the goshawks and sparrowhawks.
Webb gave a harrowing account of masked owls, and other birds and animals, being brought in suffering from poisoning.
“They come in sick, dying, or dead. Quite often, if we have had a masked owl brought in, it has signs of drooling and we know that it’s a rodenticide poisoning and the bird will be anemic and basically bleeding on the inside,” he said.
Also interviewed was Greg Irons, director of the Bonorong Wildlife Sanctuary, who said poison victims brought in for care had included Tasmanian devils and quolls.
Wildlife rescuers are now calling for more regulation on rat bait. Most rodenticides are anti-coagulant pesticides and these can be split into the less toxic first generation rodenticides and the newer, more powerful second generation poisons. At least with first generation multiple-dose poisons, birds and animals have to eat a relatively large quantity of them, and it builds up in their system slowly before it affects them. And when animals and birds show up sick at refuges they can be treated and rehabilitated. The second generation rodenticides can result in instant death or a slow and painful one.
Craig Webb is urging people with rodent problems to avoid baits altogether and to lay traps instead.
“Poisons are nasty things. Why use them, if you don’t have to?” he asks.
Bonorong, meanwhile, is hoping to get more statistics through the veterinary hospital located at the sanctuary in Brighton to assess the full scale of the problem.