DESERT ANURAN OCCURRENCE AND DETECTION IN ARTIFICIAL BREEDING HABITATS

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Abstract

One-third of known amphibian populations have become extinct, with habitat loss and degradation being the leading causes in the United States. Site occupancy has been suggested as one of the most effective state variables in describing population declines. The objectives of this study were to determine occupancy estimates of five southwestern desert anurans, accounting for imperfect detection, and to determine the main factors impacting detection. We conducted call and visual surveys on three consecutive nights after rain events at 21 breeding sites for Mexican Spadefoot (Spea multiplicata), Plains Spadefoot (Spea bombifrons), Couch’s Spadefoot (Scaphiopus couchii), Great Plains Toad (Anaxyrus cognatus), and Green Toad (Anaxyrus debilis). We used occupancy modeling to estimate the proportion of sites occupied for all species detected during the sampling period. Spea multiplicata and A. debilis were most prevalent, followed by A. cognatus, Sp. bombifrons, and Sc. couchii, respectively. In addition to the inclusion of repeated site surveys to decrease bias, incorporating visual surveys greatly improved occupancy estimates for southwestern desert anurans. Detection was highest on survey night one for Sp. multiplicata, Sp. bombifrons, Sc. couchii, and A. debilis (72.2-100%); warmer air temperature improved detection of A. cognatus. Sky conditions did not significantly influence desert anuran detectability. Immediate survey after rain events and the combination of call and visual surveys are critical to increase accuracy when studying desert anurans.

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