Cane toad and model data

Toad tracking data.xlsx - Prior to release, we attached a radio transmitter around the waist of each toad using a ball chain, a technique used extensively for radio-telemetering cane toads (after Brown et al. 2006). Transmitters were small (~1.5 cm long) and light (mean = 6.0 g) relative to toad body mass (mean = 112.8 g, 5.4% of toad body mass) (PD-2, Holohil, Carp, Ontario, Canada). Toads were placed in a tub filled with ~0.5–1 cm of water for 1–2 hours prior to release so they could fully hydrate, and we could measure their fully-hydrated body mass. We released toads at night (7:30 pm–12:00 am) into a shallow (~0.5–1 cm depth) artificial water pool that dried up by the following morning, forcing the toads to disperse. We then radio-tracked and located each toad once to twice a day (6 am–12 am), until they had lost 40% of their body mass or were found dead. We considered any change in body mass as indicative of water loss (or gain) (as in Tingley et al. 2012). A loss of 40%, or more, of initial mass was taken as a sign of severe dehydration; animals in this state were euthanized using the method described by Sharp (2011). Toads can survive losing water up to 52.6% of their body mass (Krakauer 1970), but a loss of 40% severely compromises locomotor capacity, and in the study area, death would be an inevitable outcome. Each time toads were located, we recorded their mass (when the toad could be easily moved and returned to the same position in which it was found), behavioural state (e.g. hopping, sheltering, dead), location, and microhabitat. If a toad was found dead, the site was not classified as a shelter site, unless the toad had been found sheltering there previously. When toads were not visible in burrows, they were assumed dead after 2–4 days in the same location (depending on the number of days since their initial release) and were excavated. All such cases were, in fact, dead.

Burrow transects data.xlsx - We estimated burrow availability by walking six 6x100 m transects in each site (n=12 in each habitat). Transects were walked by two observers, spaced 3 m apart, looking 1.5 m on either side for 100 m. We only counted burrows which were large enough to fit a plaster model of a toad (minimum aperture: 12.5x7.0x2.5 cm).

Model data.csv & Model temperature data.csv - To investigate rates of water loss across the landscape, we used plaster models that mimic water loss rates of live cane toads (Tingley and Shine 2011; Tracy et al. 2007). Models were soaked for ~12 hours and subsequently weighed to determine their ‘fully hydrated’ mass. We placed the models within 22 shelter sites chosen by telemetered toads and placed an additional 8 models in the open. Each model was weighed ~24 and 48 hours after placement in the field. Thermochron iButtons (Maxim Integrated, San Jose, CA, United States) recorded temperatures within the plaster models over this time period. All models placed in the open reached dry weight (< 0.05% water) within 24 hours, so all mass and temperature measurements taken beyond 24 hours were discarded. Models in burrows were placed as deep as possible, while still being able to be retrieved, resulting in placements at varying depths ranging from ~10–40 cm.

Soil data.xlsx – To further investigate the benefit provided by burrows, we collected soil samples from 10 burrows used by telemetered toads in order to calculate soil water content. We took a sample from the top soil layer, and at 10 cm and 50 cm depth (where possible) and weighed them immediately in the field. This depth gradient covered the depth of all sampled burrows. Samples were then oven dried for >8 hours and re-weighed to estimate (evaporated) water content.