Evaluating sublethal anticoagulant rodenticide exposure in deceased predatory birds of South-East Queensland, Australia

Evaluating sublethal anticoagulant rodenticide exposure in deceased predatory birds of South-East Queensland, Australia

The use of anticoagulant rodenticides (ARs) to manage rodent populations can result in unintentional lethal or sublethal
poisoning of non-target wildlife, particularly predatory birds. In south-east Queensland, Australia, rodent infestations fluctuate due to favourable environmental conditions, leading to increased AR use and incidences of secondary poisoning. Globally, lethal and sublethal AR exposure has been documented in predatory birds. However, in Australian predatory birds, both the lethal exposure limits and the impacts of sublethal exposure are poorly understood. This study examines AR exposure in 23 raptors and 1 nightjar. Postmortem liver samples were analysed using liquid chromatography mass spectrometry (LC–MS). Traumatic injuries were observed in 15 birds, and rodent remains were found in the gizzards of 9 individuals. LC–MS revealed that 13 birds had sublethal exposure to ARs, with warfarin, a first-generation AR (n=11) being the most common, followed by second-generation ARs brodifacoum (n=3), difethialone (n=1), and focoumafen (n=1). Only six of the thirteen AR-positive birds had rodent remains in their gastrointestinal tracts, highlighting the potential of AR bioaccumulation and associated impacts over time. The contribution of sublethal AR exposure to the death of these predatory birds remains unproven and underscores the need for ongoing research into AR exposure in native predatory birds, especially in areas where threatened avifauna inhabit human-dominated landscapes.