Rodent control and the high risk to raptors
With the dry summer and recent rain across the state, rats and mice are now moving indoors across the landscape in both urban and rural settings. For some time we at Landcare Tasmania and a number of our groups have been concerned about the impact poisons used to control rats and mice are having on our wildlife.
The threat is very real and some poisons are much worse than others. Wildlife specialist Nick Mooney has presented at a number of awareness raising info sessions run for groups around the state and his review paper was published in Tasmanian Bird Report Volume 38, July 2017 (Birdlife Tasmania).
Birds of prey, such as the endangered Masked Owl (right), are particularly vulnerable to rodenticides as are other predators and scavengers like quolls and devils which eat dead and dying rodents and so are poisoned themselves. But there are ways to minimise our impact.
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 you can do to limit the impact on our wildlife. For most people using a combination of the methods described below will give the best results.
Use manual traps
The old style mice and rat traps, live cage traps, plus some of their newer types 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 scavengers or predators because there are no poisons to pass on.
Use lower impact poisons
Most rodenticides (poisons designed to kill rats and mice) are based on anticoagulants 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 rodents. 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 raptors or other scavengers/predators and so can significantly affect local populations. When using rodenticides a choice to use FGARs may well make the difference for your local raptors.
"But how do I know which is which?"
Fortunately, most SGARs are clearly labelled “single dose action” and you can check the label for the active ingredients.
FGARs - Warfarin, Coumateralyl
SGARs - Brodifacoum, Bromadioline
Remember: No poison is completely safe, so use poison as a last resort.
Better prepare your facilities
How you physically prepare your property can make a difference to whether rats and mice will come in looking for food. Properly sealing houses and buildings so as to restrict entry is particularly effective, though can be difficult to achieve. Restricting the availability of food is also important, for example using rat and mice-proof compost heaps and using chicken feeders that are designed only to release food in quantities needed to feed your chickens.
And remember that others may not even know there impact, from shopping centres to your neighbours, if you are trying to protect habitat you need to get others on board, so don't forget to ask and look at the alternatives.
Have a look at Nick Mooney's review paper HERE
Check out Healthy Wildlife, Healthy Lives for a bit more detail and links to other studies.