Reproduction and Survival of the Desert Tortoise (Scaptochelys agassizii) in Ivanpah Valley, California

Turner, Frederick; Medica, Philip A.; Lyons, C.L.

doi:10.2307/1445322

Cited by 85 publications

(69 citation statements)

References 17 publications

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“…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.…”

Section: Discussionmentioning

confidence: 85%

“…Numerous factors have been identified as threats to desert tortoise populations (USFWS 1994), and these factors do not operate independently, but rather synergistically (Tracy et al 2004, USFWS 2008. Growing human populations, for example, can create resource subsidies of food and water that together allow native predator densities to increase beyond normal population levels (Goodrich & Buskirk 1995), and predation is often identified as a problem in the management and recovery of at-risk species (Gompper & Vanak 2008), including desert tortoises (Woodbury & Hardy 1948, Turner et al 1984, Berry 1986.…”

Section: Introductionmentioning

confidence: 99%

“…coyotes Canis latrans and free-roaming dogs Canis familiaris) or mountain lions Felis concolor (Woodbury & Hardy 1948, Turner et al 1984, Peterson 1994, Medica & Greger 2009); more recently, mortality of adults from common ravens Corvus corax has been observed (K. K. Drake pers. obs., D. Hinderle et al pers.…”

Section: Introductionmentioning

confidence: 99%

“…obs.). Coyote predation is the most frequently cited cause of predation on adult tortoises and has been reported to range from 18 to 30% annually during some research projects (Turner et al 1984, Peterson 1994. It has been speculated that levels of coyote predation on tortoises are inversely related to the abundance of the preferred coyote prey base of small mammals such as rodents and lagomorphs (Woodbury & Hardy 1948, Reyes Osorio & Bury 1982, Turner et al 1984; however, there has been no direct documentation of population levels of coyotes and their possible prey species for the Mojave Desert ecoregion.…”

Section: Introductionmentioning

confidence: 99%

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

Esque¹,

Nussear²,

Drake³

et al. 2010

Endang. Species. Res.

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Understanding predator-prey relationships can be pivotal in the conservation of species. For 2 decades, desert tortoise Gopherus agassizii populations have declined, yet quantitative evidence regarding the causes of declines is scarce. In 2005, Ft. Irwin National Training Center, California, USA, implemented a translocation project including 2 yr of baseline monitoring of desert tortoises. Unusually high predation on tortoises was observed after translocation occurred. We conducted a retrospective analysis of predation and found that translocation did not affect the probability of predation: translocated, resident, and control tortoises all had similar levels of predation. However, predation rates were higher near human population concentrations, at lower elevation sites, and for smaller tortoises and females. Furthermore, high mortality rates were not limited to the National Training Center. In 2008, elevated mortality (as high as 43%) occurred throughout the listed range of the desert tortoise. Although no temporal prey base data are available for analysis from any of the study sites, we hypothesize that low population levels of typical coyote Canis latrans prey (i.e. jackrabbits Lepus californicus and other small animals) due to drought conditions influenced high predation rates in previous years. Predation may have been exacerbated in areas with high levels of subsidized predators. Many historical reports of increased predation, and our observation of a rangewide pattern, may indicate that high predation rates are more common than generally considered and may impact recovery of the desert tortoise throughout its range.

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Section: Discussionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Esque¹,

Nussear²,

Drake³

et al. 2010

Endang. Species. Res.

View full text Add to dashboard Cite

show abstract

“…We then retraced the trail of thread and searched for the nest, concentrating on burrows occupied during the preceding days. Actual date of oviposition was thus based on either detection of eggs in the ground or inferred from significant weight loss (Turner et al 1984(Turner et al , 1986. After oviposition, the thread-trailing device was removed until a second clutch was detected on a subsequent X-radiograph.…”

Section: Field Techniquesmentioning

confidence: 99%

Climatic variation affects clutch phenology in Agassiz’s desert tortoise Gopherus agassizii

Lovich¹,

Agha²,

Meulblok³

et al. 2012

Endang. Species. Res.

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There is concern about how climate change might affect Agassiz's desert tortoise Gopherus agassizii, a threatened species. We studied the effects of climatic variation on clutch phenology of a population at a wind energy generation facility for 7 field seasons between 1997 and 2011. Using X-radiography, we quantified the following phenophases based on the number of calendar days to each event from 1 January: appearance and disappearance of 65 first and 53 second clutches, and inter-clutch intervals between first and second clutches. Although third clutches were rare (n = 8), they were observed in 5 of 7 yr and were produced by 8 different females, all of which produced a third clutch only once during the study. Shelled eggs were visible from as early as 11 April to as late as 28 July, and the overall time span that eggs were visible differed among years. After controlling for maternal effects, we observed statistically significant inter-annual variation in all phenophases except for inter-clutch interval. Clutch appearance was late in cool years relative to warm years and especially late after 2 consecutive cool years. Using degree day (DD) methodology, we calculated DD accumulation during the post-hibernation and nesting season for each year. We then used DD estimates for mean date of first clutch appearance to predict the mean date of first clutch appearance in subsequent years with 1 to 10 d accuracy for all but 1 yr (1998) with El Niño conditions. Clutch phenology appears to be correlated with inter-annual variation in climate and may be influenced by climatic events in previous years.

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Deserts

2015

Ecology of North America

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Reproduction and Survival of the Desert Tortoise (Scaptochelys agassizii) in Ivanpah Valley, California

Cited by 85 publications

References 17 publications

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

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

Climatic variation affects clutch phenology in Agassiz’s desert tortoise Gopherus agassizii

Deserts

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