Movement and Survival of an Endangered Amphibian: The Facultative Use of a Modified Arid Landscape by the Sonoran Tiger Salamander

Connectivity is essential for the maintenance of genetic diversity and stability of wildlife populations. However, aquatic habitats are becoming more isolated, particularly in semiarid regions of the southwestern United States. An artificial aquatic mosaic of stock tanks often replaces natural surface water on the landscape. The federally endangered Sonoran tiger salamander (STS; Ambystoma mavortium stebbinsi) is endemic to the San Rafael Valley of southeastern Arizona and northern Sonora, Mexico, where the salamander depends on stock tanks as its primary breeding habitat. The dispersal of the terrestrial phase of STS life history is the only means of responding to aquatic threats and thus is critical for the maintenance of metapopulation dynamics. However, STS ecology outside of breeding tanks is virtually unknown, and previous studies based on Ambystoma terrestrial ecology have been restricted to woodland environments in the eastern United States. Predictions from mesic environments may not apply to STS and are of little use for management and conservation. To assess STS spatial ecology, survival, and habitat use, we used internal VHF radio transmitters to track 78 adult salamanders over a two-year study. We assessed home range size and movement metrics in relation to sex, site, and body condition using generalized linear models. STS dispersed up to 974 m from the tank edge. Average net movement distance from tank edge was 403.6 m (± 225.7 m), and average 95% kernel home range was 3,053.7 m2 (± 4,511.1 m2). Maximum migration distances were higher than most Ambystoma species, but not sufficient on average to disperse to neighboring stock tanks. We found that mortality was higher than in prior Ambystoma studies. High mortality (81.03%) suggests that terrestrial dispersal is risky for STS and high mortality during terrestrial dispersal may contribute to isolated subpopulations and elevated levels of inbreeding. Management actions that improve and maintain artificial aquatic habitats on the landscape may be needed to improve connectivity and population viability for pond-breeding amphibians in arid or semiarid regions