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Kristin H. Berry

Publications and source records attributed to Kristin H. Berry.

At least 19 recordsLinked to original sources
USGS2026

Dog attacks on wild desert tortoises: A risk model

We retrospectively compiled a database of 6,727 live, wild Agassiz's desert tortoises ( Gopherus agassizii ) and evaluated them for clinical signs of trauma to shell and limbs at 50 sites in the Mojave and Colorado (western Sonoran) deserts of California, USA, spanning the years 1977–2006. Our objectives were to 1) identify tortoises with severe trauma to shell, limbs, and gular horns typically seen in attacks from dogs ( Canis familiaris ); 2) identify locations where severe injuries occurred; and 3) develop a risk model based on distances of tortoises from settlements, towns, or cities. Our models identified multiple variables of importance for tortoises with severe damage to shells, limbs, and gular horns: relative age and sex of tortoises, decades of occurrence, and location. Females and very old tortoises were more vulnerable to attacks than other tortoises. In the decades between the 1970s and 2000s, the risk of severe overall trauma to shell and limbs increased 4 times and to gular horns 16.5 times. Compared to previous decades, by the early 2000s the percent of tortoises with severe trauma increased exponentially the closer a tortoise site was to a settlement; the exponential increase began at approximately 12 km from a settlement. We suggest that the risks may be higher now because of the growth of human populations within the geographic range of the tortoise. The threats to tortoises from dogs are based on whether dogs are off-leash in the Mojave and Colorado deserts.

Arizona, California, Nevada, Utah↗
USGS2024

Potentially toxic elements in wild Agassiz’s desert tortoises: Tissue concentrations and association with disease

Background: Desert tortoise ( Gopherus agassizii ) populations have continued to decline due to infectious and other diseases, predation, and habitat alteration. The potential contribution of minerals and heavy metals to tortoise health and susceptibility to disease remains uncertain. Objective: The objective of this study was to evaluate the results of elemental analysis of trace minerals and macrominerals in scute keratin, kidney, and liver tissue from ill and dying desert tortoises salvaged for necropsy between 1993 and 2000. Methods: Salvaged tortoises were categorized by age (adult, juvenile), geographic location, and primary disease based on necropsy findings. A subset of tortoises that were injured or killed by vehicular trauma or predation but with no notable pathologic abnormalities were used as controls. A panel of 21 trace minerals and 6 macrominerals was analyzed in scute keratin, kidney, and liver tissue samples by inductively-coupled plasma spectrometry and atomic absorption spectrophotometry. Results: Necropsies were done on 46 tortoises, including 9 juveniles salvaged from 5 regions in the Colorado and Mojave deserts of California. Primary diseases were cutaneous dyskeratosis (n=9), infection/ inflammation (n=8), malnutrition (n=7), mycoplasmosis (n=5), and urolithiasis (n=3); 14 tortoises were classified as controls. Concentrations of elements differed significantly by tissue, age, desert region, and disease (P < 0.05). Tortoises with cutaneous dyskeratosis had significantly higher Se concentrations, primarily in keratin and liver, than tortoises with other diseases (P < 0.001). Juveniles were more likely than adults to have high Pb, Sn, and Zn levels (P < 0.05). All tortoises had detectable levels of more than one potentially toxic heavy metal, including As, Cd, Cr, Hg, Ni, Pb, Sn and V. Conclusions: Potentially toxic elements are frequently found in tissue from tortoises in desert regions of California, with significantly higher concentrations in diseased tortoises. Metal exposure from soils, mining, historic and ongoing military activities, and other human activities could increase susceptibility to disease in desert tortoises.

California↗
USGS2023

Selection of microhabitats, plants, and plant parts eaten by a threatened tortoise: Observations during a superbloom

Populations of the threatened desert tortoise ( Gopherus agassizii ) continue to decline throughout the geographic range, in part because of degraded and fragmented habitats in the Mojave and western Sonoran deserts. The species is herbivorous and highly selective in choice of plant species. To increase options for recovery, we analyzed behaviors, patterns of movements while foraging, and parts of plants consumed during a superbloom. We characterized foraging routes and the habitat strata and microhabitats where tortoises traveled to eat preferred wildflower species. Tortoises walked one foraging route per day in early spring, often switched to two routes per day in middle and late spring with rise of midday temperatures. They chose habitat strata (primarily hills and ephemeral stream channels) and three of seven microhabitats for foraging on preferred food plants. Preferred microhabitats were intershrub open space and small (1–2 m wide) ephemeral stream channels. They rarely took bites of forbs growing under and in the dripline of shrubs or nonnative forbs and grasses. Tortoises typically did not select specific plant parts to eat but important exceptions occurred. For example, they usually ignored the inflorescences of the annual Eremothera boothii and, when eating the non-native annual Erodium cicutarium , tended to focus on fruits. All such information aids recovery efforts to restore declining tortoise populations.

California↗
USGS2023

Variations in climate drive behavior and survival of small desert tortoises

In the Mojave Desert, timing and amounts of precipitation profoundly affect availability of water and annual plant foods necessary for the threatened Agassiz’s desert tortoise ( Gopherus agassizii ) to survive, especially during prolonged droughts. As part of recovery actions to increase declining populations, we translocated 83 juvenile and young desert tortoises raised in head-start pens for 4–10 years to a new location 15 km away during fall of 2013 and 2014. We tracked them for 9 years during a megadrought, during multiple years of low rainfall and a few years when precipitation neared or exceeded long-term norms. We evaluated behaviors and how precipitation and forage availability affected survival. At the end of the study, 21.6% of tortoises were alive and 6 had grown to adulthood. Annual models of survival indicated that tortoise size was the driving variable in most years, followed by number of repeatedly used burrows during periods of temperature extremes. Other variables affecting survival in ≥1 year were vegetation, movements during the first 2 years post-translocation, and condition index, a measure of health. Tortoises moved more, expanded home ranges, and grew rapidly in years when winter rainfall approached or exceeded long-term norms and annual plants were available to eat. During dry years, movements and growth were limited. Exceptions to this pattern occurred in the last year of study, a dry year: tortoises grew, moved more, and home ranges increased. The increase in size and approaching adulthood may have stimulated greater travelling. Some left the study area, indicating a need for large release areas. We may have aided survival by offering water twice yearly when handling, because some tortoises drank and increased in mass up to 40%. Prolonged droughts and hotter temperatures can limit recovery of populations, reduce survival of young tortoises, and increase the time to maturity.

California↗
USGS2023

Bilateral palpebral reduction and concurrent mycoplasmosis in a wild Agassiz's desert tortoise (Gopherus agassizii)

A wild Agassiz's desert tortoise, Gopherus agassizii , with bilateral eyelid reduction and plaques of tissue covering the superior surface of both corneas was examined in the field and subsequently submitted to the University of Florida for diagnostics. Polymerase chain reaction (PCR), from a swab of both corneas, was positive for Mycoplasma agassizii . Two months later, the tortoise was euthanatized and necropsied. There was increased bulbar exposure associated with dermal excoriation of periocular scales in both superior and inferior palpebra resulting in an increased palpebral fissure opening. Concurrently, there was bilateral conjunctivitis of the nictitating membranes and squamous metaplasia of the bulbar conjunctiva. Using PCR, Mycoplasma testudineum , another pathogen of tortoises, was identified in both nasal cavities, and the upper respiratory tract histopathological findings were consistent with those described for M . testudineum in Agassiz's desert tortoises. Although eye disease has been reported in desert and gopher ( Gopherus polyphemus ) tortoises with mycoplasmosis, widespread loss of palpebral tissue, conjunctivitis of the nictitans, and squamous metaplasia of the bulbar conjunctiva have not been reported in tortoises.

Veterinary Opthalmology↗
USGS2023

Drivers of survival of translocated tortoises

Translocation of animals, especially for threatened and endangered species, is a currently popular but very challenging activity. We translocated 158 adult Agassiz's desert tortoises ( Gopherus agassizii ), a threatened species, from the National Training Center, Fort Irwin, in the central Mojave Desert in California, USA, to 4 plots as part of a long-distance, hard-release, mitigation-driven translocation to prevent deaths from planned military maneuvers. We monitored demographic and behavioral variables of tortoises fitted with radio-transmitters from 2008 to 2018. By the end of the project, 17.72% of tortoises were alive, 65.82% were dead, 15.19% were missing, and 1.27% were removed from the study because they returned to Fort Irwin. Mortality was high during the first 3 years: >50% of the released animals died, primarily from predation. Thereafter, mortality declined but remained high. After 10.5 years, survival was highest, 37.50% (15/40), on the plot closest to original home sites, whereas from 2.56% to 23.68% remained alive on the other 3 release plots. Surviving tortoises settled early, repeatedly using locations where they constructed burrows, compared with tortoises that died or disappeared. Models of behavioral and other variables indicated that numbers of repeatedly used locations (burrows) were a driver of survival throughout the study, although plot location, size and sex of tortoises, and distance traveled were contributors, especially during early years. Because >50% mortality occurred, we considered this translocation unsuccessful. The study area appeared to be an ecological sink with historical and current anthropogenic uses contributing to habitat degradation and a decline in both the resident and released tortoises. Our findings will benefit design and selection of future translocation areas.

California↗
USGS2023

Sonoran desert tortoise: Gopherus morafkai

Sonoran Desert Tortoise Gopherus morafkai has most recently been assessed for The IUCN Red List of Threatened Species in 2019. Gopherus morafkai is listed as Vulnerable under criteria A2abce+4abce.

Arizona, Sonora↗
USGS2023

Techniques for restoring damaged Mojave and western Sonoran ecosystems, including those for threatened desert tortoises and Joshua trees

Ecological restoration has potential for contributing to conservation activities for threatened Mojave desert tortoises ( Gopherus agassizii ) and Joshua trees ( Yucca brevifolia , Y. jaegeriana ) and their broader ecosystems in the Mojave and western Sonoran deserts. To be effective, restoration actions deployed strategically need to halt and reverse habitat degradation, replenish or enhance resources used by both species (e.g., large shrubs for protection of tortoises and nurse plants facilitating recruitment of Joshua tree seedlings), and ideally foster resilience during likely future environmental changes. We synthesized restoration techniques and their effectiveness in the Mojave and western Sonoran deserts, provide estimated costs of candidate techniques, and anticipate future research needs for effective restoration in changing climates and environments. Over 50 published studies in the Mojave and western Sonoran deserts demonstrate that restoration can improve soil features (e.g., biocrusts), increase cover of native perennial and annual plants, enhance native seed retention and seed banks, and reduce risk of fires to conserve mature shrubland habitat. We placed restoration techniques into three categories: restoration of site environments, revegetation, and management actions to limit further disturbance and encourage recovery. Within these categories, 11 major restoration techniques (and their variations) were evaluated by at least one published study and range from geomorphic (e.g., reestablishing natural topographic patterns) and abiotic structural treatments (e.g., vertical mulching) to active revegetation (e.g., outplanting, seeding). For example, 16 outplanting studies assessed performance of 46 species to begin identifying top-performing species, associated treatments (e.g., protection from herbivory) required to aid outplant survival, and potential for outplants to trigger formation of self-sustaining populations. Creosote bush (Larrea tridentata), a shrub that tortoises use for cover and that serves as a nurse plant for Joshua tree recruitment, achieved at least 50% survival in five of eight studies. Estimated costs for restoring desert habitats varied primarily with the severity of the disturbance, site factors including the diversity of vegetation that was lost, logistical factors such as accessibility of sites (influencing transportation costs), and the cost-effectiveness of the restoration techniques chosen. The review highlights six major research and adaptive management needs for advancing desert habitat restoration. These needs include: 1) continued development of innovative techniques and bet-hedging approaches to provide managers with “tool boxes” of candidate treatments to deploy in dynamic environmental and management conditions, 2) identifying how to optimize spatial deployment of limited restoration resources, 3) developing practical techniques for reducing non-native annual grasses across spatial scales, 4) improving linkages between habitat enhancements and short- and long-term indicators of tortoise usage and responses and Joshua tree population sustainability, 5) mitigating multiple, interacting stressors with cumulative impacts, and 6) integrating biotic (e.g., seeding) and abiotic (e.g., fencing, shade structures) treatments to complement each other at site and landscape scales in dynamic climates and environments. It is possible that bet-hedging approaches employing multiple treatment types (or phased treatments across years) and greater incorporation of abiotic treatments, which are less sensitive to timing of precipitation compared with biotic treatments, will become increasingly important under future climates projected to be drier and more variable. Existing research suggests that restoration can be deployed effectively even under adverse climatic conditions, but success requires identifying suitable techniques tailored to dynamic environments.

Arizona, California, Nevada, Sonora↗
USGS2022

A novel herpesvirus detected in 3 different species of chelonians

Herpesviruses are found in free-living and captive chelonian populations, often in association with morbidity and mortality. To date, all known chelonian herpesviruses fall within the subfamily Alphaherpesvirinae . We detected a novel herpesvirus in 3 species of chelonians: a captive leopard tortoise ( Stigmochelys pardalis ) in western TX, USA; a steppe tortoise ( Testudo [ Agrionemys ] horsfieldii ) found near Fort Irwin, CA, USA; and 2 free-living, three-toed box turtles ( Terrapene mexicana triunguis ) found in Forest Park, St. Louis, MO. The leopard tortoise was coinfected with the tortoise intranuclear coccidian and had clinical signs of upper respiratory tract disease. The steppe tortoise had mucopurulent nasal discharge and lethargy. One of the three-toed box turtles had no clinical signs; the other was found dead with signs of trauma after being observed with blepharedema, tympanic membrane swelling, cervical edema, and other clinical signs several weeks prior to death. Generally, the branching order of the turtle herpesviruses mirrors the divergence patterns of their hosts, consistent with codivergence. Based on phylogenetic analysis, this novel herpesvirus clusters with a clade of viruses that infect emydid hosts and is likely of box turtle origin. Therefore, we suggest the name terrapene alphaherpesvirus 3 (TerAHV3) for the novel virus. This virus also has the ability to host-jump to tortoises, and previously documented herpesviral morbidity tends to be more common in aberrant hosts. The relationship between clinical signs and infection with TerAHV3 in these animals is unclear, and further investigation is merited.

Journal of Veterinary Diagnostic Investigation↗
USGS2021

Development of demographic models to analyze populations with multi-year data—Using Agassiz’s Desert Tortoise (Gopherus agassizii) as a case study

We developed a model for analyzing multi-year demographic data for long-lived animals and used data from a population of Agassiz’s desert tortoise ( Gopherus agassizii ) at the Desert Tortoise Research Natural Area in the western Mojave Desert of California as a case study. The study area was 7.77 square kilometers and included two locations: inside and outside the fenced boundary. The wildlife-permeable, protective fence was designed to prevent entry from vehicle users and sheep grazing. We collected mark-recapture data from 1,123 tortoises during seven annual surveys consisting of two censuses each over a 34-year period. Additional data were collected when marked tortoises were recovered dead and removed between survey years. We used a Bayesian modeling framework to develop a multistate Jolly-Seber model because of its ability to handle unobserved (latent) states and modified this model to incorporate the additional data from non-survey years. Three size-age states (juvenile, immature, adult), sex (female, male), two location states (inside and outside the fenced boundary), and three survival states (not-yet-entered, entered/alive, and dead/removed) were incorporated into the model. We calculated population densities and estimated probabilities of growth of the tortoises from one size-age state to a larger size-age state, survival after 1 year and 5 years, and detection. Our results show a declining population with low estimates for survival after 1 year and 5 years. The probability for tortoises to move from outside to inside the boundary fence was greater than for tortoises to move from inside the fence to outside. The probability for detecting tortoises differed by size-age state and was lowest for the smallest tortoises and highest for the adult tortoises. The framework for the model can be used to analyze other animal populations where vital rates are expected to vary depending on multiple individual states.

Open-File Report↗
USGS2021

Gopherus agassizii

A provisional Red List Assessment of the widespread Desert Tortoise, Gopherus agassizii ( sensu lato ), was performed at a Desert Tortoise Council workshop in 2010 and updated by the IUCN Tortoise and Freshwater Turtle Specialist Group (TFTSG) in 2011, at which time the Mojave Desert subpopulation, now considered G. agassizii ( sensu stricto ) following taxonomic analysis and splitting into three separate species ( G. agassizii , G. morafkai , and G. evgoodei ), was assessed as Critically Endangered A2bce+A4bce based on population reduction (decreasing density), habit loss of over 80% over three generations (90 years), including past reductions and predicted future declines, as well as the effects of disease (upper respiratory tract disease / mycoplasmosis). Gopherus agassizii ( sensu stricto ) comprises tortoises in the most well-studied 30% of the larger range; this portion of the original range has seen the most human impacts and is where the largest past population losses had been documented. A recent rigorous range-wide population reassessment of G. agassizii ( sensu stricto ) has demonstrated continued adult population and density declines of about 90% over three generations (two in the past and one ongoing) in four of the five G. agassizii recovery units and inadequate recruitment with decreasing percentages of juveniles in all five recovery units. As such, we reaffirm the prior assessment of the taxonomically restricted Mojave Desert Tortoise, G. agassizii , as Critically Endangered, and add criterion “a” for direct population observations: CR A2abce+A4abce. The previously defined widespread species G. agassizii ( sensu lato ) was last assessed as Vulnerable on the IUCN Red List in 1996; a separate assessment currently in progress by the TFTSG for the Sonoran Desert Tortoise, G. morafkai (previously considered part of G. agassizii ) has provisionally assessed that species as Vulnerable.

Arizona, California, Nevada, Utah↗
USGS2020

Refining genetic boundaries for Agassiz’s desert tortoise (Gopherus agassizii) in the western Sonoran Desert: The influence of the Coachella Valley on gene flow among populations in southern California

Understanding the influence of geographic features on the evolutionary history and population structure of a species can assist wildlife managers in delimiting genetic units (GUs) for conservation and management. Landscape features including mountains, low elevation depressions, and even roads can influence connectivity and gene flow among Agassiz’s desert tortoise (Gopherus agassizii) populations. Substantial changes in the landscape of the American Southwest occurred during the last six million years (including the formation of the Gulf of California and the lower Colorado River), which shaped the distribution and genetic structuring of tortoise populations. The area northwest of the Gulf of California is occupied by the Salton Trough, including the Coachella Valley at its northern end. Much of this area is below sea level and unsuitable as tortoise habitat, thus forming a potential barrier for gene flow. We assessed genetic relationships among three tortoise populations separated by the Coachella Valley. Two adjacent populations were on the east side of the valley in the foothills of the Cottonwood and Orocopia mountains separated by Interstate 10. The third population, Mesa, was located about 87 km away in the foothills of the San Bernardino Mountains at the far northwestern tip of the valley. The Cottonwood and Orocopia localities showed genetic affiliation with the adjacent Colorado Desert GU immediately to the east, and the Mesa population exhibited affiliation with both the Southern Mojave and Colorado Desert GUs, despite having a greater geographic distance (0.5x–1.5x greater) to the Colorado Desert GU. The genetic affiliation with the Colorado Desert GU suggests that the boundary for that GU needs to be substantially extended to the west to include the desert tortoise populations around the Coachella Valley. Their inclusion in the Colorado Desert GU may benefit these often overlooked populations when recovery actions are considered.

California↗
USGS2020

The catastrophic decline of tortoises at a fenced natural area

Agassiz’s desert tortoise ( Gopherus agassizii ), a threatened species of the southwestern United States, has severely declined to the point where 76% of populations in critical habitat (Tortoise Conservation Areas) are below viability. The potential for rapid recovery of wild populations is low because females require 12–20 years to reach reproductive maturity and produce few eggs annually. We report on a 34‐year mark‐recapture study of tortoises initiated in 1979 at the Desert Tortoise Research Natural Area in the western Mojave Desert, California, USA, and provide substantive data on challenges faced by the species. In 1980, the United States Congress designated the Research Natural Area and protected the land from recreational vehicles, livestock grazing, and mining with a wildlife‐permeable fence. The 7.77‐km 2 study area, centered on interpretive facilities, included land both within the Natural Area and outside the fence. We expected greater benefits to accrue to the tortoises and habitat inside compared to outside. Our objectives were to conduct a demographic study, analyze and model changes in the tortoise population and habitat, and compare the effectiveness of fencing to protect populations and habitat inside the fence versus outside, where populations and habitat were unprotected. We conducted surveys in spring in each of 7 survey years from 1979, when the fence was under construction, through 2012. We compared populations inside to those outside the fence by survey year for changes in distribution, structure by size and relative age, sex ratios, death rates of adults, and causes of death for all sizes of tortoises. We used a Bayesian implementation of a Jolly Seber model for mark‐recapture data. We modeled detection, density, growth and transition of tortoises to larger size‐age classes, movements from inside the protective fence to outside and vice versa, and survival. After the second and subsequent survey years, we added surveys to monitor vegetation and habitat changes, conduct health assessments, and collect data on counts of predators and predator sign. At the beginning of the study, counts and densities for all sizes of tortoises were high, but densities were approximately 24% higher inside the fence than outside. By 2002, the low point in densities, densities had declined 90% inside the fence and 95% outside. Between 2002 and 2012, the population inside the fence showed signs of improving with a 54% increase in density. Outside the fence, densities remained low. At the end of the study, when we considered the initial differences in location, densities inside the fence were roughly 2.5 times higher than outside. The pattern of densities was similar for male and female adults. When evaluating survival by blocks of years, survivorship was higher in 1979–1989 than in 1989–2002 (the low point) and highest from 2002 to 2012. Recruitment and survival of adult females into the population was important for growing the population, but survival of all sizes, including juveniles, was also critical.

California↗
USGS2020

Turtles and tortoises are in trouble

Turtles and tortoises (chelonians) have been integral components of global ecosystems for about 220 million years and have played important roles in human culture for at least 400,000 years. The chelonian shell is a remarkable evolutionary adaptation, facilitating success in terrestrial, freshwater and marine ecosystems. Today, more than half of the 360 living species and 482 total taxa (species and subspecies combined) are threatened with extinction. This places chelonians among the groups with the highest extinction risk of any sizeable vertebrate group. Turtle populations are declining rapidly due to habitat loss, consumption by humans for food and traditional medicines and collection for the international pet trade. Many taxa could become extinct in this century. Here, we examine survival threats to turtles and tortoises and discuss the interventions that will be needed to prevent widespread extinction in this group in coming decades.

Current Biology↗
USGS2020

An uncertain future for a population of desert tortoises experiencing human impacts

We evaluated the status of a population of Mojave Desert Tortoises ( Gopherus agassizii ), a threatened species, in the El Paso Mountains of the northwestern Mojave Desert in California, USA. The study area lies north of and adjacent to a designated critical habitat unit for the species, is adjacent to a state park, and is a short distance from the Desert Tortoise Research Natural Area. We randomly sampled 373 1-ha plots from a 239.1-km 2 area in the mountain range to determine demographic attributes of the population, vegetation associations, predator presence, and human uses. Live and dead G. agassizii and sign (burrows, scats, tracks) occurred on 35.7% of plots. Densities of adults were higher than in adjacent critical habitat, and threats (traumatic injuries, infectious and other diseases) were similar to those reported elsewhere in the geographic range. Signs of human use were evident on 98.4% of plots. We used a multimodel approach to determine distribution of G. agassizii in relation to vegetation, anthropogenic, and predator variables. Vegetation, predators, trash, mining activity, and vehicles were important factors affecting the distribution and intensity of tortoise sign. We concluded that this population is in a downward trend, like other populations in the western Mojave Desert. The high death rate of adults, low population density, high human visitor use, and ongoing decline in the adjacent critical habitat unit indicate that a viable population is unlikely to persist in the study area. The future for the population found in the El Paso Mountains might depend on survival in the adjacent roadless El Paso Mountains Wilderness Area.

California↗
USGS2020

Feral burros and other influences on desert tortoise presence in the western Sonoran Desert

Across the globe, conflicting priorities exist in how land and resources are managed. In the American West, conflicts are common on public lands with historical mandates for multiple uses. We explored the impacts of multiple uses of land in a case study of Agassiz's Desert Tortoises ( Gopherus agassizii ), a federally threatened species, in the western Sonoran Desert. The tortoise has declined for many reasons, most of which relate to management of land and habitat. Frequently cited causes are livestock grazing, roads, vehicle-oriented recreation, predators, and disease. In spring of 2009, we conducted a survey to evaluate relationships between desert tortoises, vegetation associations, topography, predators, and anthropogenic uses. We sampled a 93-km 2 area with 200 independent 1-ha plots. Density (± SE) of adult tortoises was low, 2.0 ± 1.0/km 2 , and the annualized death rate for adults during the 4 yr preceding the survey was high, 13.1%/yr. We observed tortoise sign, most of which was recent, on 22% of the 200 plots, primarily in the southwestern part of the study area. More tortoise sign occurred on plots with Brittlebush ( Encelia spp.) vegetation at higher elevations. Most plots (91.0%) had ≥1 human-related impacts: feral burro scat ( Equus asinus ; 84.0%), recent vehicle tracks and trails (34.0%), trash (28.0%), burro trails and wallows (26.5%), and old vehicle tracks (24.0%). We used a multimodel approach to model presence of tortoise sign on the basis of 12 predictor variables, and calculated model-averaged predictions for the probability of tortoise presence. Importance values revealed two apparent top drivers: feral burros and vegetation association. This is the first study to identify a negative association between presence of desert tortoises and feral burros.

Arizona, California↗
USGS2019

Gopherus agassizii (Cooper 1861) – Agassiz’s Desert Tortoise, Mojave Desert Tortoise

The Mojave Desert Tortoise, Gopherus agassizii (Family Testudinidae), is a large terrestrial species that can reach >370 mm in straight midline carapace length (CL) but most individuals are smaller. Both sexes reach adulthood at 12 to 21 years and ca. 180 mm CL. The species is sexually dimorphic, with males typically larger than females; sexual characteristics of males become more obvious with increasing size and age. Females lay from 1 to 10 eggs per clutch and from 0 to 3 clutches annually, with eggs hatching after 67 to 104 days. Populations of G. agassizii have declined rapidly over the last several decades. Habitat throughout the geographic range has experienced major losses, degradation, and fragmentation as a result of urban and agricultural development, livestock grazing, military activities, transportation and utility corridors, high levels of visitor use, vehicle-oriented recreation, and energy development. Disturbed habitats were vulnerable to invading non-native grasses and forbs, creating an unnatural and destructive grass-fire cycle. When consumed by tortoises as their only diet, non-native (and native) grasses are harmful because of limited nutrients. Additionally, subsidized predators (Common Ravens, Coyotes, and dogs), infectious diseases, drought, and vandalism, add to the catastrophic effects of habitat loss and degradation. Tortoise populations have declined rapidly in density, and most populations are below viability, with fewer than 3.9 adults/km2. These declines occurred despite protections afforded by federal and state laws and regulations, ca. 26,000 km2 of federally designated critical habitat units, two Recovery Plans, and efforts to reduce the negative impacts of human activities. As noted by Allison and McLuckie (2018), the negative population trends in most of the critical habitat units suggest that under current conditions G. agassizii is on the path to extinction. Distribution. – USA. Distributed in parts of the southern Great Basin, Mojave, and western Sonoran deserts in southeastern California, southern Nevada, northwestern Arizona, and southwestern Utah, north and west of the Grand Canyon/Colorado River complex, with the exception of a small population east of the Colorado River. Synonymy. – Xerobates agassizii Cooper 1861, Testudo agassizii, Gopherus agassizii, Gopherus polyphemus agassizii, Scaptochelys agassizii, Xerobates lepidocephalus Ottley and Velázques Solis 1989. Subspecies . – None currently recognized. Status. – IUCN 2019 Red List: Vulnerable (VU A1acde+2cde; assessed 1996) ; TFTSG Provisional Red List: Critically Endangered (CR; assessed 2011, 2018); CITES: Appendix II (Testudinidae spp.); US ESA: Threatened.

Arizona, California, Nevada, Utah↗