Leap, frog: toad-proof agricultural infrastructure for landscape-level management of cane toads.

Agriculture is an increasingly dominant land use across the globe. Habitat modification associated with agricultural expansion is both directly and indirectly impacting biodiversity. One way that agricultural habitat modification impacts biodiversity is by facilitating the spread and persistence of invasive species. The provision of artificial water sources to sustain livestock in semi-arid regions of Australia, for example, has allowed toxic invasive cane toads (Rhinella marina) to spread into otherwise inhospitable regions. Throughout the region, artificial watering points consist of bore-fed dams that facilitate toad breeding and hydration. Modelling suggests that preventing cane toads from accessing artificial watering points in arid regions could dramatically limit their spread. Thus, the challenge is to design watering infrastructure that serves agricultural needs but denies water to toads during the dry season. In this study, we tested the ability of cane toads to overcome barriers to reach water. We conducted experiments testing the jumping and climbing ability of adult cane toads, as well as their capacity to jump or climb over fences and into water troughs. Our findings revealed that > 99% of toads are unable to breach barriers ≥ 51 cm high. We also found that material choice and trough design affect the probability of breach by toads. Shade cloth was a more effective fencing material cover than was plastic, and concrete troughs with a rounded lip proved more difficult for toads to enter than plastic troughs with a grippable edge. Commercially available precast concrete troughs were found to be particularly effective at excluding toads, and are still an accessible height for calves. These findings suggest that fencing and/or converting open dams to tank-fed cattle troughs could prevent cane toad persistence and spread through arid landscapes while maintaining agricultural operations. Thus, simple upgrades to agricultural infrastructure could prove crucial in reducing the invasive distribution of toads and preventing further spread into biodiversity-rich areas like the Pilbara region of Western Australia.