Masked Owl corpse Photo B Wykes
In a PhD study at Edith Cowan University, Mike Lohr used Boobooks as a readily accessible, ‘sentinel’ nocturnal species to test for levels of rodenticides, with freshly dead birds from various causes contributed from across the south west including from Margaret River.
The results from analysis of livers were shocking, with 74 per cent containing a range of rodenticide chemicals. Even where not directly resulting in death, many levels were sufficiently high to likely have contributed to death from apparently unrelated factors such as vehicle impact, disease and starvation.
ECU researcher Dr Mike Lohr’s study of rodenticides in Boobooks set alarm bells ringing.
Many day as well as night birds and mammals are at risk of ingesting rodent poison by preying on live and dead rats and mice as well as reptiles and insects that access the baits.
This was less of a problem when products were based on ‘first generation anticoagulants’ such as warfarin and coumatetralyl. These baits need to be eaten in several meals to be fatal, can be effectively metabolised by our wildlife when ingested through secondary pathways, and poisoning can be treated effectively with Vitamin K.
However now poisons based on ‘Second Generation Anticoagulant Rodenticides’ (SGARs) such as brodifacoum and bromodialone dominate retail shelves. These are promoted as killing rodents with a single dose but that is also the fate of wildlife or pets that directly ingest the poison, as veterinarians attest. Furthermore, the rodent still takes days to die from internal bleeding, in which time they can ingest several ‘single dose’ meals and are easy prey. SGARs ingested through primary and secondary pathways are not readily metabolised, persisting and accumulating in the livers of wildlife and pets, and not responsive to treatment.
Sadly, the finding that rodenticides are showing up in local wildlife was not unexpected because problems arising from SGARs have already been identified throughout the world for children, pets and wildlife. Several developed countries have banned or restricted use of the same second generation poisons that are sold without regulation by Australian supermarkets, hardware stores and farm suppliers.
The Australian Pesticides and Veterinary Medicines Authority is conducting a review of the status of anticoagulant rodenticides on the basis of concerns for worker exposure, public health and environmental safety.
Rat problems, owl solutions
Some limb dislocation and pulverising is needed before a fledgling Masked Owl swallows a rat whole for dinner in this video clip: