An ongoing study by Michael Lohr, a PhD student at Edith Cowan University (ECU), has found a concerning link between commonly used rat and mouse poisons and the deaths of Boobook owls in Perth Hills and the Perth metropolitan area. So far, 55 Southern Boobooks (Ninox novaseelandiae) found dead have been tested for exposure to eight different anticoagulant rodenticides which are used in Australia. These poisons work as blood thinners. They accumulate in the liver shortly after they enter the body and some can stay there for months. If Boobooks eat multiple mice poisoned with anticoagulant rodenticides, over time, the poison can accumulate to high enough levels to be fatal.
Preliminary results of the study show that in the Perth Metro area and residential areas of the Perth Hills, almost 90% of Boobooks had some amount of rodenticide exposure. A few individuals tested positive for as many as five different rodenticides. About 17% of all Boobooks from these areas had high enough levels of rodenticide to potentially kill them. Almost all of the rodenticides detected were the longer-lasting second generation anticoagulant rodenticides. Only two Boobooks showed exposure to a first generation anticoagulant rodenticide. In both Boobooks, the amount detected was so low it would not be likely to cause any harm. Most of the rodenticides detected in Boobooks are available to the public at supermarkets and hardware stores and are commonly used to control rodents around the home. However, a small number of Boobooks were exposed to rodenticides which are used mostly by pest control services in commercial or industrial buildings. Interestingly, none of the Boobooks from large patches of bushland or agricultural areas had any detectable rodenticide exposure.
The research is still ongoing but it is already clear that the widespread use of rat and mouse poison around homes is having an impact on some of our native wildlife. Testing is about to begin on an additional batch of Boobook liver samples. Some of these samples will fill in gaps in areas where no Boobooks have been tested. Some are also from agricultural areas and will help determine whether rodenticide poisoning is as much of a problem outside of residential areas. In the future, testing of additional species, especially ones that are already rare or endangered will help in understanding whether these rodenticides are a threat to the recovery of these species. Testing species of animals which the owls feed on will also help explain exactly how the rodenticides move up the food chain and create a clearer picture of which other species could be affected.
Photo: Paula Strickland