Return to the wild: Translocation as a tool in conservation of the Desert Tortoise (Gopherus agassizii)

Abstract

inducing carelessness in water conservation. In addition to generally investigating the efficacy of translocation, we compared the effects of continuing with the effects of ceasing the holding facility's water supplementation regimen. After exposure to one of the two water regimens, all tortoises were given the opportunity to hydrate immediately prior to release.We examined behavior, body mass, carapace length, movement, and mortality of tortoises for two activity seasons following release to the wild. Water supplementation was correlated with high rates of carapace growth and distant movements by males after release.Lengthy movements following translocation may be problematic for conservation planning, but this should be evaluated in light of the goals and circumstances of each translocation project. Although the mortality rate was 21.4% in 1997, data suggest that drought conditions at the site rather than the translocation itself negatively affected the tortoises.None of the tortoises died during their second season at the site. Our results indicate that translocation should be considered a useful tool in conservation of the Desert Tortoise.

Effects of subsidized predators, resource variability, and human population density on desert tortoise populations in the Mojave Desert, USA

“…This was counter to what might be expected, as male tortoises are known to have larger home ranges (Berry 1986, O'Connor et al 1994, Harless et al 2009) and generally move greater distances, especially after translocation (Nussear 2004, Field et al 2007). Elevated female mortality has been reported elsewhere (SAIC 1993, Field et al 2007, and Riedle et al (2010) found higher mortality among female than among male desert tortoises at a Sonoran Desert site. Most mortality at the Sonoran site was a result of mountain lion predation and could have affected females more in early spring, because they tend to be more active earlier in the season than males in the Sonoran Desert.…”

“…Similar observations of predation have been made by those conducting desert tortoise research, beginning with the seminal work of Woodbury & Hardy (1948), who observed that predation on desert tortoises increased in 1945 and 1946 when the numbers of rabbits and rodents were low. Similar observations continued across decades of field research, and each time a low prey base was invoked -although in none of these cases was the prey base actually quantified (Turner et al 1984, Peterson 1994, Nussear 2004, Field et al 2007. Bridging this gap in ecological information would be an excellent way to test this hypothesis; however, this type of work is extremely difficult to implement and fund, as annual rainfall conditions and productivity are highly variable in the Mojave Desert (Beatley 1969(Beatley , 1976.…”

“…While it is difficult to discern between predation and scavenging (e.g. Peterson 1994, Nussear 2004, Field et al 2007, we think that the vast majority of these tortoises were killed by predators, because of the very detailed research histories of each tortoise in combination with the frequency of monitoring, the fact that the tortoises were overtly healthy when last observed, and the evidence of predation in relation to the carcasses (i.e. fresh predator tracks and scat, and chew marks).…”

“…Furthermore, since the 1980s, many 100s of radio-telemetered tortoises have been followed at multiple sites for multiple years with multiple research teams, and incidence of high mortality was quite rare. Other hypothesized mechanisms for heightened predation levels include increased movements of tortoises that were translocated (Nussear 2004, Field et al 2007, potential unavailability or unfamiliarity with locations of cover sites, food and water, and the attraction of predators to areas with increased tortoise densities and increased human activity. However, translocated, control, and resident animals did not differ statistically in mortality rates from one another.…”

Growing and shrinking in the smallest tortoise, Homopus signatus signatus: the importance of rain

“…115 days of the activity period), and that this shrinkage was reversible (K.J. Field, personal communication;Field et al 2007). We do not have suYcient data on survivorship for H. s. signatus, but the growth subsequent to shrinking suggests that shrinking is a reversible eVect of starvation.…”