Hibernaculum Use by a Population of Desert Tortoises (Gopherus agassizii) in the Sonoran Desert

Bailey, Scott J.; Schwalbe, Cecil R.; Lowe, Charles H.

doi:10.2307/1564985

Cited by 35 publications

(23 citation statements)

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“…Thus our results should be applicable to Fort Irwin as a whole, and seem to accord with prior knowledge of tortoise distribution on Joshua Tree National Park (J. Freilich, personal observation ). Our findings broadly agree with those of Bailey et al (1995) on hibernaculum habitats. It is possible that our results may apply to the whole of the western Mojave Desert; the field validation that would be required to determine this is beyond the scope of this study, and we strongly suggest that the model should be tested at other locations.…”

Section: Discussionsupporting

confidence: 91%

“…Burrows are made under rocks or in soil and may be as much as 5 m in length but are usually <1 m deep (Burge 1978, Bulova 1994). Patterns of burrow use are sex specific (Bailey et al 1995) and may reflect complex social interactions among individual tortoises (Bulova 1997). Burrow living can make tortoises difficult to find, particularly in drought years when the animals seal themselves behind a wall of dirt and stay underground to conserve water.…”

Section: Introductionmentioning

confidence: 99%

“…Sonoran Desert populations (east of the Colorado River) are believed to spend more time in rocky or mountainous terrain than their Mojave counterparts (Barrett 1990, ). Hibernacula tend to be on south‐facing slopes in silty or diatomaceous soils, often under layers of volcanic tuff (Bailey et al 1995). Beyond this, little detail has emerged identifying specific factors explaining tortoise presence or absence in an area (Germano et al 1994, Schamberger and Turner 1986).…”

Section: Introductionmentioning

confidence: 99%

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Regression-Tree Modeling of Desert Tortoise Habitat in the Central Mojave Desert

Andersen

Watts

Freilich

et al. 2000

Ecological Applications

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This paper describes an interdisciplinary study of the habitat requirements of threatened desert tortoises (Gopherus agassizii) on eight 225‐ha study plots in a 14 000 ha study area near the southern boundary of the U.S. Army's National Training Center at Fort Irwin in the central Mojave Desert of southern California. The objective of the study was to produce an empirical, statistical, GIS‐based model of desert tortoise habitat use based on a combination of field data and data derived from various spatial databases, including satellite imagery. A total of 11 primary and secondary data layers constitute the spatial database used for this project. Vegetation and tortoise relative density data were obtained from field surveys. Regression‐tree methods were used to develop the statistical model. The tree has 11 terminal nodes and a residual mean deviance of 1.985. Out of 73 potential predictors in the model specification, only eight were selected by the algorithm to be used in construction of the tree. The model suggests that tortoises tend to occur on southwest exposures and loamy soils, and that they avoid stony soils, north exposure, and areas of very low plant cover. Our results imply that soil composition and parent materials can be important determinants of habitat suitability for desert tortoises, and for burrowing animals in general. Our study also provides an example of how the interdisciplinary integration of biology, earth sciences, GIS, and statistical modeling can reveal important aspects of the habitat requirements of endangered species.

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Section: Discussionsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Regression-Tree Modeling of Desert Tortoise Habitat in the Central Mojave Desert

Andersen

Watts

Freilich

et al. 2000

Ecological Applications

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“…Seven out of eight tortoises in 1991 were in burrows with some degree of southern exposure, and all but one were on slopes of >49x. Mean male hibernation time was 154 days, and females 131, at one site ; at another it was 140 for males and 118 for females (Bailey et al, 1995). These differences were not significant because of large variability, but there is a definite trend, as females were also more active in the spring.…”

Section: Terrestrial Turtlesmentioning

confidence: 84%

“…There is little change in mass over the winter among juveniles (Nagy, Morafka & Yates, 1997), indicating that neither depletion of energy stores nor water loss are stressors during hibernation ; this was also the case for adults in Nevada (Nagy & Medica, 1986). In Arizona, using conservative estimates of burrow length, Bailey, Schwalbe & Lowe (1995) found males used longer hibernacula (118.3 cm) than females (24.4 cm), which they state is typical in the Mojave and Sonoran deserts. As a result, there were wider temperature fluctuations in the females' burrows.…”

Section: Terrestrial Turtlesmentioning

confidence: 91%

The ecology of overwintering among turtles: where turtles overwinter and its consequences

2006

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Turtles are a small taxon that has nevertheless attracted much attention from biologists for centuries. However, a major portion of their life cycle has received relatively little attention until recently - namely what turtles are doing, and how they are doing it, during the winter. In the northern parts of their ranges in North America, turtles may spend more than half of their lives in an overwintering state. In this review, I emphasise the ecological aspects of overwintering among turtles, and consider how overwintering stresses affect the physiology, behaviour, distributions, and life histories of various species. Sea turtles are the only group of turtles that migrate extensively, and can therefore avoid northern winters. Nevertheless, each year a number of turtles, largely juveniles, are killed when trapped by cold fronts before they move to safer waters. Evidently this risk is an acceptable trade-off for the benefits to a population of inhabiting northern developmental habitats during the summer. Terrestrial turtles pass the winter underground, either in burrows that they excavate or that are preformed. These refugia must provide protection against desiccation and lethal freezing levels. Some burrows are extensive (tortoise genus Gopherus), while others are shallow, or the turtles may simply dig into the ground to a safe depth (turtle genus Terrapene). In the latter genus, freeze tolerance may play an adaptive role. Most non-marine aquatic turtles overwinter underwater, although Clemmys (Actinemys) marmorata routinely overwinters on land when it occurs in riverine habitats, Kinosternon subrubrum often overwinters on land, and several others may overwinter terrestrially on occasion, especially in more southern climates. For northern species that overwinter underwater, there are two physiological groupings, those that are anoxia-tolerant and those that are relatively anoxia-intolerant. All species fare well physiologically in water with a high partial pressure of oxygen (PO2). A lack of anoxia tolerance limits the types of habitats that a freshwater turtle may live in, since unlike sea turtles, they cannot travel long distances to hibernate. Hatchlings of some species of turtles spend their first winter in or below the nest cavity, while hatchlings of other species in the same area, including northern areas, emerge in the autumn and presumably hibernate underwater. All hatchlings are relatively anoxia-intolerant, and there are no studies to date of where hatchling turtles that do not overwinter in or below the nest cavity spend their first winter. Equally little is known of the ontogeny of anoxia tolerance, other than that adults of all species are more anoxia-tolerant than their hatchlings, probably because of their better ossified shells, which provide adults with more buffer reserves and a larger site in which to sequester lactate. The northern limits of turtles are most likely determined by reproductive limitations (time for egg-laying, incubation, and hatching) than by the rigors of hibernation. Mortalit...

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Risk factors influencing brumation success in captive tortoises in the United Kingdom

2022

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Background This survey of tortoise owners was performed to investigate the factors contributing to morbidity and mortality during and post‐brumation in captive Testudo species in the United Kingdom. Methods Information regarding a total of 270 tortoises was included in the study, from 252 completed surveys. Binary logistic regression and multivariate modelling were used to evaluate the potential predictors associated with brumation mortality and those associated with post‐brumation problems. Results A 7.78% mortality rate was found, with 7.22% of surviving tortoises reported to have post‐brumation health concerns. Brumation in a garden and an uncontrolled reduction of temperature prior to brumation were the main risk factors for morbidity and mortality in the study. Conclusions Veterinarians should be aware of these risk factors to ensure they target husbandry and brumation advice to owners of tortoises to reduce these risks.

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Hibernaculum Use by a Population of Desert Tortoises (Gopherus agassizii) in the Sonoran Desert

Cited by 35 publications

References 0 publications

Regression-Tree Modeling of Desert Tortoise Habitat in the Central Mojave Desert

Regression-Tree Modeling of Desert Tortoise Habitat in the Central Mojave Desert

The ecology of overwintering among turtles: where turtles overwinter and its consequences

Risk factors influencing brumation success in captive tortoises in the United Kingdom

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