A few years ago a bird of prey feared by my neighbourhood songsters stopped visiting my garden and I had my suspicions as to the reason why.
At the time wildlife biologist Nick Mooney was warning that a new range of anticoagulant rodenticides were taking a toll on birds of prey.
Mooney said that a more powerful second generation of the rodenticides which hit with a single dose had replaced a slow-acting earlier version. Both the rodenticides were still on the market, and still are, and Mooney urged farmers and gardeners with raptors on their properties to consider the earlier versions, which ultimately still did the job of killing rats and mice but did not have the same potency to immediately kill birds.
Mooney’s warning struck a chord with me because not only was I long longer hearing the chattering alarm calls of my resident new holland honeyeaters, I had noticed a spate of chicken coops springing up in the extensive gardens of properties in my peri-urban neighbourhood. I surmised that this surge in backyard farming had prompted a surge in rodents, and thus the application of rodenticides.
Mooney is again drawing attention to the menace of these powerful rodenticides, as we approach spring when rat and mice populations are on the rise.
Mooney has written a paper on the issue for the annual Tasmanian Bird Report, soon to be published by BirdLife Tasmania.
Mooney, however, is not pointing a finger at gardeners wanting to protect their chicks, eggs and crops, but merely suggesting an alternative strategy that is less dangerous to birds and indeed native mammals.
The less harmful rodenticides with warfarin or coumatetralyl as the active ingredient carry the trademark of Ratsak Double Strength and Racumin. Those more dangerous to birds are Talon and Ratsak Fast Action.
Mooney also points out there are alternatives to anticoagulants which are harmless to birds.
In his paper, Mooney gives details of bird species confirmed by necropsy to have been killed by the poisons. Especially at risk are masked owls, 11 dying in the Hobart area in recent years, including one recovered from Salamanca Place.
Mooney points out this number is probably only the tip of the iceberg. The vast majority of the masked owl population occurs in rural landscapes inter-dispersed with patches of dry woodland, villages and towns. Excluding the woodland, Mooney estimates that about two-thirds of the estimated population of a little less than 1000 birds of the rare and threatened owl could be exposed to the second-generation rodenticides. Of these, Mooney estimates that 10 per cent, or 100 birds annually, could be killed.
Other birds listed as being killed by the powerful rodenticides include boobook owls, white goshawks and the brown goshawks of my garden.
When Mooney first raised the issue I wrote about it extensively and spoke to hobby farmers in my home valley in Hobart where suburbia meets bush who might be using the poisons.
I am pleased to report that in recent years the brown goshawk, and a smaller goshawk, the collared sparrowhawk, have returned, much to the annoyance of the honeyeaters.