Habitat drives dispersal and survival of translocated juvenile desert tortoises

Abstract

1. In spite of growing reliance on translocations in wildlife conservation, translocation efficacy remains inconsistent. One factor that can contribute to failed translocations is releasing animals into poor-quality or otherwise inadequate habitat. 2. Here, we used a targeted approach to test the relationship of habitat features to posttranslocation dispersal and survival of juvenile Mojave desert tortoises Gopherus agassizii. 3. We selected three habitat characteristicsrodent burrows, substrate texture (prevalence and size of rocks) and washes (ephemeral river beds)that are tied to desert tortoise ecology. At the point of release, we documented rodent burrow abundance, substrate texture and wash presence and analysed their relationship to the maximum dispersal. We also documented the relative use by each individual for each habitat characteristic and analysed their relationships with survival and fatal encounters with a predator in the first year after release. 4. In general, the presence of refugia or other areas that enabled animals to avoid detection, such as burrows and substrate, decreased the overall mortality as well as predator-mediated mortality. The presence of washes and substrate that enhanced the tortoises' ability to avoid detection also associated with the reduced dispersal away from the release site. These results indicate an important role for all three measured habitat characteristics in driving dispersal, survival or fatal encounters with a predator in the first year after translocation. 5. Synthesis and applications. Resource managers using translocations as a conservation tool should prioritize acquiring data linking habitat to fitness. In particular, for species that depend on avoiding detection, refuges such as burrows and habitat that improved concealment had notable ability to improve the survival and dispersal. Our study on juvenile Mojave desert tortoises showed that refuge availability or the distributions of habitat appropriate for concealment are important considerations for identifying translocation sites for species highly dependent on crypsis, camouflage or other forms of habitat matching.

A range‐wide model of contemporary, omnidirectional connectivity for the threatened Mojave desert tortoise

“…Although tortoise site fidelity and selective foraging within desert washes has been shown in previous studies (Nafus et al. ), our analysis also showed that tortoises were more likely to make longer distance movements in areas where washes were present. The probability of movement declined with the highest values of wash density, which may underlie their preference for smaller stream channels that are 1–2 m wide (Jennings and Berry ).…”

Discriminating patterns and drivers of multiscale movement in herpetofauna: The dynamic and changing environment of the Mojave desert tortoise

“…Subadults, which typically exhibit shorter movements and smaller home ranges (Farnsworth et al., ), were encountered more frequently than expected near minor roads. Local use areas near minor roads were also relatively steep, rough, and had a relatively larger area classified as wash, characteristics associated with reduced predation risks among subadults (Hagerty et al., ; Nafus, Esque, Averill‐Murray, Nussear, & Swaisgood, ). Additional investigation is needed to improve understanding of the potential influence of minor roads on desert tortoise movement, such as the possibility of concentrating local activity by providing embankments or other structures for burrow creation or increased resource availability (Latch, Boarman, Walde, & Fleischer, ).…”

Calibrating an individual‐based movement model to predict functional connectivity for little owls

“…The challenge, however, is that these processes must be calibrated to data, for example empirical observations of a species’ habitat use and movement during dispersal (Nafus et al. , Signer and Ovaskainen , Buderman et al. ).…”