Factors affecting diurnal shelter use by the cane toad, Bufo marinus

We experimentally examined patterns of diurnal retreat site use by 50 adults of Bufo marinus in a 45 m(2) enclosure containing 18 artificial shelters, nine each in its eastern and western halves. At 15 times (samples), each separated by 48 h, we captured each toad and recorded its location within the enclosure. We also recorded the soil moisture and temperature under each shelter. After data were taken, toads were released at the center of the enclosure. There were five experimental treatments, each carried out over three consecutive samples: an initial unwatered treatment (U1), water applied with a hose to saturate the western half of the enclosure (W), a second unwatered treatment (U2), water applied to the eastern half of the enclosure (E), and a third unwatered treatment (U3). The watering treatments affected the distribution of toads within the enclosure; by the end of each watering treatment, many toads had switched to the watered half of the enclosure. Toad density under shelters increased with increasing soil moisture. When soil moisture was greater than zero, more loads were found under shelters with higher soil temperatures. Toads aggregated under shelters, suggesting that they preferred sites already occupied by other individuals. They also returned to the same shelter in consecutive samples more frequently than expected if shelter selection were random. Aggregation and shelter fidelity may serve to reduce effective surface area:volume ratios and may also allow tends to take advantage of increased soil moisture caused by individuals urinating in shelter sites.