Type: report

Article abstract: In 2003, we implemented a new monitoring program for the endangered arroyo toad (Bufo californicus) on Marine Corps Base Camp Pendleton (MCBCP). To address the problems associated with large variations in adult toad activity, we employed a spatial and temporal monitoring approach that tracks the presence of arroyo toad breeding populations by documenting the presence of eggs and larvae. Sites were surveyed up to four times per year to calculate and account for imperfect detection probabilities. We also continued night surveys for adult toads from the monitoring program implemented by Dan Holland in 1996. This report details the results and analyses of the first three years of the spatial monitoring program and a decade of adult count transects. During this study, three years of highly variable rainfall had large impacts on arroyo toad breeding and breeding habitat. After a normal rainfall year in 2003, minimal rainfall in 2004 resulted in the complete lack of breeding and recruitment within the San Mateo and San Onofre watersheds, which were largely or completely dry. In 2005, twice the normal rainfall created huge surges in all watersheds. Scouring of stream and river channels substantially reduced aquatic vegetative cover and washed away portions of adjacent banks and floodplains. In tracking both the proportion of area with surface water and the proportion of wet area occupied by breeding toads, we found that even though surface water availability was highly variable (44-95%), the overall extant of breeding toads in wetted areas was relatively stable (77-95%) with no significant change over the three year period. The night survey count data from 1996 to present also shows that arroyo toad activity has had extremely high annual variability (ranging +/- 44% of mean), but has been relatively stable over the last decade. We found the probability of detecting arroyo toad larvae was positively associated with low flow shallow water and negatively associated with non-native species. These two variables were correlated with one another. During the arroyo toad breeding season, non-native species were associated with deep 1 and faster flowing water. Since the amount of low flow shallow water was highly variable within each season, this factor was predictive of detecting tadpoles on a given survey, but not of annual occupancy. For annual occupancy and adult counts, we found compelling evidence that arroyo toad dynamics differ among the watersheds according t