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These data were compiled to evaluate the reproductive ecology of Agassiz's desert tortoises (Gopherus agassizzi) in the Sonoran Desert of California using two populations within Joshua Tree National Park, including five reproductive seasons that spanned 20 years (1997-1999, 2015-2016). Compared to their conspecifics inhabiting the Mojave Desert, the reproductive ecology of G. agassizii in the Sonoran Desert is understudied. Climatic variation between the two deserts can affect reproductive ecology, including fecundity and clutch phenology. Mature female tortoises (straight-line carapace length ≥ 20 cm) outfitted with radiotransmitters were located and X-radiographed approximately every 10-14 days during the reproductive...
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This dataset provides spatial predictions of habitat suitability for Gopherus agassizii (Agassiz’s desert tortoise), Gopherus morafkai (Morafka’s desert tortoise) and a pooled-species model under current conditions (1950 – 2000 yr). The raster layers contained here accompany the manuscript Inman et al. 2019 and were used to evaluate subtle ecological niche differences between G. agassizii and G. morafkai, and identify local species-environment relationships. Spatial predictions of habitat suitability were created using MaxEnt version 3.4.0 (Phillips et al., 2006), a widely-used software for SDM in presence-background frameworks. Detailed methods are provided in Inman et al. 2019. Inman et al. 2019. Local niche...
To elucidate ecological effects of variation in the temporal distribution of a limiting resource (water in the Mojave Desert), energetics of two free-living populations of desert tortoises (Gopherus [=Xerobates] agassizii) were studied concurrently over 18 mo with use of doubly-labeled water. Field metabolic rates (FMR) and feeding rates (estimated from rates of water influx and rates of change in dry mass) were highly variable. This variability was manifested at several levels, including seasonal changes within populations, year-to-year differences within populations, and differences between populations. Underlying observed patterns and contrasts was considerable variation among individuals. Much of the variation...
1. Heating and cooling rates of the desert tortoise, Gopherus agassizii, were measured in the field and in the laboratory. 2. Heating rates in the field were up to ten times faster than cooling rates. 3. Under controlled conditions, heating rates equalled rates of cooling. 4. Heart rates during heating were significantly faster than during cooling at any particular body temperature. 5. Subcutaneous neck temperatures did not differ from cloacal temperatures during heating or cooling, suggesting a state of continuous vasodilation. 6. Results are interpreted as suggesting that behavioral postures and activities play a greater role than physiology in the determination of thermal exchange rates of the desert tortoise....
In the Sonoran Desert of North America, populations of the desert tortoise (Gopherus agassizii) occur in rocky foothills throughout southwestern Arizona and northwestern Mexico. Although tortoise populations appear to be isolated from each other by low desert valleys, individuals occasionally move long distances between populations. Increasingly, these movements are hindered by habitat fragmentation due to anthropogenic landscape changes. We used molecular techniques and radiotelemetry to examine movement patterns of desert tortoises in southern Arizona. We collected blood samples from 170 individuals in nine mountain ranges and analyzed variability in seven microsatellite loci to determine genetic differentiation...
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These data were acquired from 7 study sites distributed across the range of Gopherus agassizii. Data were collected from 1997 to 2002 as part of three separate studies, although data were not collected at all sites in each year. Radio-transmitters were attached to the carapace of 151 females and VHF radio-telemetry was used to relocate animals to assess reproductive status. Egg production was determined from X-radiographs taken weekly/biweekly intervals (depending on the study) using a portable X-ray machine between April and July or August of each year. In addition, the mean carapace length (MCL) of each tortoise was measured at each time of capture or recapture using calipers (mm). A nesting event was recorded...
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These data were compiled to evaluate reproductive output of Agassiz's desert tortoises (Gopherus agassizzi) in relation to environmental and individual-level variables. We collected data from four study sites in the Sonoran Desert of California, including two separate populations within Joshua Tree National Park, one population located on the northern versant of the Orocopia Mountains, and one population located at the extreme western end of the Coachella Valley. These data represent eight reproductive seasons that spanned over 20 years (1997-2000, 2015-2018). These data were compiled and added to a larger database with additional records collected by other scientists from eight other study sites in order to detect...
1. 1. Deep body and shell surface temperatures were monitored via radio-telemetry from unrestrained desert tortoises in their natural habitat. 2. 2. The surface of the carapace acts as a buffer against solar radiation, resulting in deep body temperatures up to 10�C below shell surface at the time of the midday retreat to burrows. 3. 3. The burrow of the desert tortoise provides the only ambient temperatures at ground level which are below the lethal range for this species during midday hours. 4. 4. Evening retreat to burrows permits an extension of higher body temperatures into the mid-evening hours. 5. 5. The use of evening burrow retreats lessens in mid-summer. This behavioral change results in lower body temperatures...
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This USFWS data set has been modified by NatureServe to include critical habitat only within the Central Basin and Range, and Mojave Basin and Range ecoregions, and further modified to include only the desert tortoise (Gopherus agassizii). These data identify, in general, the areas where final critical habitat exist for species listed as endangered or threatened.
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This dataset represents current terrestrial intactness values (estimated at the 1km level) within the modeled distribution of the Desert tortoise (Gopherus agassizii). Terrestrial intactness is high in areas where development is low, vegetation intactness is high, and fragmentation is low. Consequently, this dataset serves as a general* indication of habitat quality within the distribution of this conservation element. Estimates of current terrestrial intactness were generated by an EEMS fuzzy logic model that integrates multiple measures of landscape development and vegetation intactness, including agriculture development (from LANDFIRE EVT v1.1), urban development (from LANDFIRE EVT v1.1 and NLCD Impervious Surfaces),...
The seasonal reproductive cycles of male and female desert tortoises (Gopherus agassizii) were studied under semi-natural conditions. Tortoises were maintained in outdoor pens subject to ambient weather conditions and received supplemental food and water. Heparinized blood samples were collected monthly using jugular puncture. Ovarian follicular growth and egg development were monitored using ultrasonography. Mating was observed in the fall (following nesting) and the spring (prior to nesting). Vitellogenesis occurred during the fall prior to hibernation. Nesting was observed from May-early July with females producing one or two clutches. Clutches ranged from 2-7 eggs. Both males and females displayed seasonal testosterone...
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The Moj_ConservationAreas layer is a mosaic of data including the Arizona, California, Nevada, and Utah Areas of Critical Environmental Concern (ACEC), Critical Habitat Unit (CHU), the Red Cliffs Desert Reserve (RCDR), the Desert Tortoise Conservation Center (DTCC), the Desert National Wildlife Refuge, State and National Parks, National Monuments, National Conservation Areas, Beaver Dam Wash National Conservation Area, and the Boulder City Conservation Easement (BCCE). Landownership classification for Wilderness Areas and Wilderness Study Areas, Department of Defense and Department of Energy were also included.
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This USFWS data set has been clipped by NatureServe to include critical habitat only within the Central Basin and Range, and Mojave Basin and Range ecoregions, and extracted to include only the desert tortoise (Gopherus agassizii) critical habitat areas. These data identify, in general, the areas where final critical habitat exist for species listed as endangered or threatened.
Incubation temperature has a direct effect on sex determination of the desert tortoise. Low temperatures (26.0-30.6 C) produce males and high temperatures (32.8-35.3 C) produce females. Pivotal temperature is approximately 31.8 C. Macroscopic and microscopic anatomy of the gonads is similar to that of other turtles. Hatching success and survival is very good between 28.1 and 32.8 C in dry sand (-5000 kPa). Incubation at 35.3 C is lethal for 72% of the eggs and produces weak hatchlings that die within 45 days. Wet sand (-5 kPa) is lethal for desert tortoise eggs. Hatchling size was dependent upon egg size and incubation condition. Hatchlings from eggs incubated at 32.8 and 35.3 C were significantly smaller than hatchlings...
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The Desert Tortoise (Gopherus agassizii) species distribution model includes a continuous probability surface from the USGS statistical model completed by Kenneth E. Nussear, Todd C. Esque, Richard D. Inman, Leila Gass, Kathryn A. Thomas, Cynthia S. A. Wallace, Joan B. Blainey, David M. Miller, and Robert H. Webb and a binary layer produced by the Conservation Biology Institute. The binary layer depicts predicted suitable habitat using the equal training sensitivity and specificity threshold (0.506). The binary output was also processed to exclude agriculture, developed, and disturbed areas, based on the DRECP land cover/natural vegetation dataset provided by Todd Keeler-Wolf of the CA Dept. of Fish and Game. The...
The desert tortoise Gopherus agassizii is federally listed as Threatened because of documented declines in some populations, yet the proximate causes of these declines are not well understood. With use of radiotelemetry, I monitored a total of 55 individual tortoises at two Mojave Desert sites over three years. Both populations suffered high adult mortality during an extreme drought period, but the temporal pattern and inferred proximate causes of mortality differed between sites. At the eastern Mojave site, no telemetered tortoises died in 1988 or 1989, but 41% died in 1990. All nine carcasses were found and only one showed any evidence of predation or scavenging. Tortoises that died had symptoms of dehydration...
Habitat modeling offers an approach to understanding some management problems of desert tortoises (Gopherus agassizii) and to focusing new research efforts. Modeling can provide (1) a method to organize existing information, (2) a means to identify whether physical habitat or some factor outside the scope of the habitat model is limiting populations, (3) a method to integrate habitat into resource development planning, and (4) a mechanism for focusing research on missing species-habitat information. Published in Herpetologica, volume 42, issue 1, on pages 134 - 138, in 1986.
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These data refer to habitat and activity data collected for female desert tortoises being monitored as part of a study on juvenile rearing and translocation for population augmentation purposes. The females were affixed with radio transmitters and radio tracked at least monthly to maintain knowledge of whereabouts. During those tracking events activity data were collected (surface or in burrows) and predominate habitat community recorded. Ancillary to this goal a habitat use study was conducted to determine the type of habitat occupied by females. Thus the data reference female morphology, activity, and a single instance of habitat use.
    map background search result map search result map Desert tortoise - Habitat Intactness, DRECP Desert Tortoise - Species Distribution Model, DRECP Reproductive ecology data for female Agassiz's desert tortoises (Gopherus agassizii) in Joshua Tree National Park, USA Spatial Predictions of Mojave Desert Tortoise, Sonoran Desert Tortoise and Pooled Species Habitat Suitability for present-day (1950 – 2000 yr) BLM REA MBR 2010 Final Critical Habitat (Polygonal Features) BLM REA MBR 2010 Conservation Areas in the Mojave Desert BLM REA CBR 2010 PLII CBR crithab poly tortoise Agassiz's desert tortoise and egg data from the Sonoran Desert of California (1997-2000, 2015-2018) Mojave Desert Tortoise (Gopherus agassizii) Morphometrics and Egg Data from Seven Sites across the Mojave, (1997-2002) Activity and habitat selection by female desert tortoises in Mojave National Preserve, California USA 2011 - 2013 Reproductive ecology data for female Agassiz's desert tortoises (Gopherus agassizii) in Joshua Tree National Park, USA Activity and habitat selection by female desert tortoises in Mojave National Preserve, California USA 2011 - 2013 Agassiz's desert tortoise and egg data from the Sonoran Desert of California (1997-2000, 2015-2018) BLM REA MBR 2010 Final Critical Habitat (Polygonal Features) BLM REA CBR 2010 PLII CBR crithab poly tortoise Mojave Desert Tortoise (Gopherus agassizii) Morphometrics and Egg Data from Seven Sites across the Mojave, (1997-2002) Desert tortoise - Habitat Intactness, DRECP BLM REA MBR 2010 Conservation Areas in the Mojave Desert Desert Tortoise - Species Distribution Model, DRECP Spatial Predictions of Mojave Desert Tortoise, Sonoran Desert Tortoise and Pooled Species Habitat Suitability for present-day (1950 – 2000 yr)