Bait uptake by scavengers in tropical waterbodies

In tropical Australia, conditioned taste aversion can buffer vulnerable
native predators from the invasion of a toxic prey species (cane toads,
Rhinella marina). Thus, we need to develop methods to deploy
aversion-inducing baits in the field, in ways that maximize uptake by
vulnerable species (but not other taxa). We constructed and field-tested
baiting devices, in situ with wild animals. Apparatus were set next to
waterbodies and baited concurrently at multiple locations (over water,
water’s edge and on the bank). Baits were checked and replaced twice daily
during the trial; remote cameras recorded visitation by native predators.
Bait longevity was compared at sun-exposed and shaded locations over 12
hours. The strength required to remove baits from apparatus was measured
in varanids and crocodiles. The device promoted high rates of bait uptake
by freshwater crocodiles (47% baits consumed), varanid lizards (19% baits
consumed), and non-target taxa (34% baits consumed). Targeting specific
predators can be achieved by manipulating bait location and time of
deployment, as well as the force required to dislodge the bait. Crocodiles
were best targeted with over-water baits, whereas varanid lizards
preferred baits located at the edges of waterbodies. When testing bait
longevity in ambient conditions, during the daytime baits desiccated fully
within 12h, and faster in the sun than in the shade. Based on studies
using captive animals, the ‘pulling force’ strength of reptilian predators
scaled with body size and was greater in crocodiles than in varanid
lizards. We present the first conservation baiting protocol designed
specifically for reptiles. Our results demonstrate the feasibility of
widespread and taxon-specific deployment of aversion-inducing baits to
buffer the impacts of invasive cane toads, and our methods are applicable
(with modification) to other research and management programs globally.