Predictive Models for Calling and Movement Activity of the Endangered Houston Toad

Abstract

Anuran monitoring has increased in recent years in response to global population declines. Delineating abiotic factors that influence anuran activity patterns is important for maximizing monitoring and research efficiency. The Houston toad (Bufo (Anaxyrus)houstonensis) was the first amphibian to be listed as federally endangered in the United States, and populations have continued to decline since it was listed. In this study we investigated the influence of six abiotic factors and one biotic factor on Houston toad calling activity and terrestrial movement in the Lost Pines ecoregion of Texas. Using program PRESENCE, we treated the factors as survey-specific covariates to determine their influence on detection probabilities, and thus presumably activity levels. We found that average daily absolute humidity, average daily wind speed, and presence/absence of Houston toad calling activity the previous night were important factors influencing calling activity, and average daily absolute humidity and detection/non-detection of Houston toad movement activity the previous night were important factors influencing movement activity. We also found that multiple survey years were necessary to delineate influential factors for this species, a result with implications for activity patterns of other rare anurans. The results of this study contribute to our understanding of amphibian activity patterns, and will improve the efficiency of future Houston toad research and monitoring efforts.