I know when goshawks are visiting my garden without having to actually see them. The alarm calls of the new holland honeyeaters announce the brown goshawk and the smaller collared sparrowhawk are in the vicinity and stalking birds in canopy and shrubbery.
No raptor instills such terror in the honeyeaters and other garden birds than the goshawks which, unlike other birds of prey, generally kill by ambush in trees, although they will also pin both bird and small mammal to the ground if they get the chance.
So frequent is the alarm call of honeyeaters, I grow concerned when they fall silent because it indicates something in turn has happened to the goshawks.
I learned a few years back from wildlife biologist Nick Mooney that a new range of quick-action, single-dose rodenticides was inflicting a terrible toll on our birds of prey, writing a column about it at the time.
Now I learn that Mooney’s warnings have been taken up by Landcare Tasmania, which has launched its own Rodenticide Community Awareness Program to alert members to the dangers these man-made chemicals are posing to the environment.
Birds of prey, especially those that target rats and mice, are particularly vulnerable, including the endangered masked owl. When raptors eat dead or dying rodents they are poisoned themselves.
Controlling introduced rats and mice is a necessity for many of us, whether on farms, in the bush or in town. However, there are several things we can do to limit the impact on our wildlife. A combination of rodent-control methods can achieve results.
The old-style mice and rat traps, live cage traps, plus some newer types of control like electric traps, still have a role to play in controlling rodent populations, particularly when not in large numbers. Such mechanical or electric deaths are safe for predators or scavengers, such as quolls which will also take poisoned bait, because there are no poisons to pass on.
The same cannot be said for what are termed impact poisons.
Most rodenticides are based on anticoagulant chemicals that kill by promoting uncontrolled internal bleeding. Older types of anticoagulants, called First Generation Anticoagulant Rodenticides (FGARs), require rodents to take multiple doses and therefore kill more slowly but have less effect on animals that eat poisoned rats and mice. More recently developed Second Generation Anticoagulant Rodenticides (SGARs) are used much more widely, mainly because of the convenience of their single-dose effect. They kill rats and mice more quickly but more residual poison is ingested by scavengers or predators and so these rodenticides can significantly affect local wildlife populations. When using rodenticides a choice to use FGARs may well make the difference for our local raptors.
Fortunately, most SGARs are clearly labelled “single-dose action” and labels can be checked for active ingredients. Among these are the trade names Brodifacoum and Bromadioline which should be used in controlled circumstances. Less toxic FGARs are Warfarin and Coumateralyl.
Details of the program and links to Nick Mooney’s research can found at www.landcaretas.org.au/projects