Evaluation of oral baits and distribution methods for Tasmanian devils (Sarcophilus harrisii)

Abstract

Context: Diseases are increasingly contributing to wildlife population declines. Tasmanian devil (Sarcophilus harrisii) populations have locally declined by 82%, largely owing to the morbidity and mortality associated with two independent transmissible devil facial tumours (DFT1 and DFT2). Toxic baits are often used as a management tool for controlling vertebrate pest populations in Australia, but in other areas of the world, oral baits are also used to deliver vaccines or pharmaceuticals to wildlife. Aim: Our goal was to evaluate the potential use of edible baits as vehicles for vaccine delivery to Tasmanian devils. Method: We first tested bait palatability with captive devils. Bait interactions were recorded, and consumption and bait interaction behaviours were quantified. We next trialled baits containing inert capsules as potential vaccine containers in captivity. After confirming bait palatability in captivity, ground baiting was trialled at six field sites and monitored using camera traps. Finally, an automated bait dispenser was trialled at field sites to attempt to limit bait consumption by non-target species. Key results: Captive devils consumed all types of placebo baits, but consumed a higher percentage of ruminant- and fish-based baits than cereal-based baits. Captive devils also consumed inert capsules inserted into placebo baits. Ground-baiting trials in the field showed that 53% of baits were removed from bait stations, with 76% of the removals occurring on the first night. Devils were suspected or confirmed to remove about 7% of baits compared with 93% by non-target species. We also evaluated an automated bait dispenser, which reduced bait removal by non-target species and resulted in over 50% of the baits being removed by devils. Conclusions: This study demonstrated that captive and wild devils will accept and consume placebo versions of commercial baits. Bait dispensers or modified baits or baiting strategies are needed to increase bait uptake by devils. Implications: Bait dispensers can be used at a regional scale to deliver baits to devils. These could potentially be used as vaccine-delivery vehicles to mitigate the impacts of disease on devil populations.