Mortality Of Tortoises Research Articles

Design of Roadway Barriers to Reduce Desert Tortoise Mortality on Paved Road Infrastructure

Design of Roadway Barriers to Reduce Desert Tortoise Mortality on Paved Road Infrastructure

Genetic analyses are more sensitive than morphological inspection at detecting the presence of threatened Mojave desert tortoise (Gopherus agassizii) remains in canid scat and raven pellets

AbstractSubsidization of predator populations increases predation pressure on prey species, which is exacerbated when natural resources are scarce. Estimating the frequency of predation by subsidized predators on vulnerable species, especially low‐density, long‐lived species such as the federally threatened Mojave desert tortoise (Gopherus agassizii), allows landscape managers to evaluate the need for actions like reducing subsidies, discouraging predation by taste aversion, or predator removal. Most studies of Mojave desert tortoise predation have relied on morphological analysis to identify hard parts in predator scat. Here, we developed and validated a qPCR assay to test for the presence of Mojave desert tortoise in DNA extracted from scat and pellets. We used the assay to detect tortoise DNA in scat and pellets collected in a conservation easement adjacent to Boulder City, Nevada, from three Mojave desert tortoise predators: coyotes (Canis latrans), desert kit foxes (Vulpes macrotis arsipus), and common ravens (Corvus corax)—all of which consume anthropogenic resources. We compared the results of our qPCR assay to results from morphological analysis of the same samples and found that the qPCR method is much more sensitive at detecting the presence of tortoise remains. Although neither method can determine whether consumption was the result of predation or scavenging, nor how many individual tortoises were consumed, our findings indicate that conservation managers may benefit from focusing efforts on reducing subsidies that attract and support predators and on reducing tortoise mortality from predation.

High female desert tortoise mortality in the western Sonoran Desert during California’s epic 2012-2016 drought

We conducted population surveys for desert tortoisesGopherus agassiziiat 2 nearby sites in the western Sonoran Desert of California, USA, from 2015-2018, during the driest ongoing 22 yr period (2000-2021) in the southwestern USA in over 1200 yr. We hypothesized that drought-induced mortality would be female-biased due to water and energy losses attributable to egg production during protracted periods of resource limitation. At the higher-elevation, cooler, wetter Cottonwood site from 2015-2016, the sex ratio of live adult tortoises was biased toward males and the sex ratio of tortoises estimated to have died during the intensified drought conditions from 2012-2016 was essentially even. At the lower-elevation, warmer, drier Orocopia site from 2017-2018, the sex ratio of live adult tortoises was biased toward males and the sex ratio of tortoises with estimated times of death from 2012-2016 was biased toward females. High female mortality at the Orocopia site may have resulted from the interaction of drought effects and the bet-hedging reproductive strategy of tortoises wherein they continue to produce clutches of eggs in drought years. Annual reproductive output results in an estimated loss of up to 13.5% of female tortoise body mass including over 0.20 l of water. Combined with dehydration during severe droughts, these losses may compromise their ability to survive droughts lasting more than 2 yr. The low tortoise density and high mortality of females observed may reflect reduced survival of tortoises near the southern edge of their range due to climate change, including protracted and intensified droughts.

Identification of a novel mortality-associated Helicobacter species in gopher tortoises (Gopherus polyphemus), qPCR test development and validation, and correlation with mortality in a wildlife rehabilitation population

The genus Helicobacter includes spiral-shaped bacteria in the phylum Proteobacteria, class Epsilonproteobacteria, order Campylobacteriales, that have been associated with disease in animals, including reptiles. Three wild gopher tortoise (Gopherus polyphemus) index cases presented between 2012 and 2019 with nasal discharge, lethargy, and weight loss. Cytological examination of nasal discharge from all 3 tortoises identified marked heterophilic and mild histiocytic rhinitis with abundant extracellular and phagocytized spiral shaped bacteria that stained positive with Warthin-Starry stain. Polymerase chain reaction (PCR) and sequencing of the 16S rRNA gene revealed this to be a novel Helicobacter species. Two tortoises died despite treatment attempts, and the third was moribund and was euthanized. Histological examination of the nasal mucosa (n = 3) showed granulocytic to lymphocytic rhinitis with variable mucosal hyperplasia, erosion, and ulceration; Warthin-Starry staining highlighted the presence of spiral bacteria in the untreated tortoise. Genus-specific primers were designed, and the gyrA and groEL genes were amplified by PCR and sequenced. Phylogenetic analysis shows that this organism and other previously characterized Helicobacter from tortoises form a clade. Development and cross-validation of two qPCR diagnostic assays for the gyrA and groEL genes showed significant correlation of the results of two assays (P < 0.0001). These assays were used to survey nasal wash samples from 31 rehabilitating gopher tortoises. Mortality of tortoises significantly correlated with higher Helicobacter loads detected by qPCR (P = 0.028). Appropriate quarantine protocols for tortoises during rehabilitation should consider this organism. Upper respiratory disease in tortoises may involve complex microbial ecology; factors beyond Mycoplasmopsis (Mycoplasma) agassizii should be taken into account.

Leopard tortoise Stigmochelys pardalis (Bell, 1928) mortality caused by electrified fences in central South Africa and its impact on tortoise demography

ABSTRACT The leopard tortoise (Stigmochelys pardalis) is among the most ubiquitously distributed chelonian species in Africa. As with other chelonians, however, the species’ slow growth rate, coupled with low survivorship of juveniles, make it susceptible to declines under regimes of environmental perturbation. Here we studied the impact of electrified fences, a key source of mortality for many South African terrestrial vertebrate taxa, on leopard tortoise mortality in the Free State Province (Jacobsdal district) and Northern Cape Province (Strydenburg district), and its implications for survivorship of this population. Our results show a strong selection bias towards larger (breeding age) individuals that, given the life history of the species, should have strong (negative) consequences for populations. Using data for tortoise populations from other regions as a baseline for survivorship rates in populations unaffected by fencing, we derived a size-structure matrix model to evaluate the impact on population growth rates. Population projections, taking into account variation in survivorship and reproductive rates across and within size classes, indicated substantially higher risk of negative population growth (and eventual extinction) in populations affected by electrified fences. These results confirm that fencing is a conservation problem for the leopard tortoise population in this, and probably other regions, and highlights an urgent need for more intensive regulation of electrified fencing practices among landowners.

Tortoise mortality along fence lines in the Karoo region of South Africa

Fencing, including electric fencing, is widely used across South Africa for livestock and game ranching practices. Leopard tortoises (Stigmochelys pardalis) are particularly prone to being killed by electric fences, but no published studies have assessed the impact of fence structure or quantified tortoise mortality along non-electric fences. This is a conservation concern, especially because South Africa is home to more tortoise species than any other country. This study relates tortoise mortality associated with electrified and non-electrified fences to fence structure, and uses transects away from fences as a comparison to estimate the impact of fences on mortality. All fence types had significantly higher tortoise mortality than open veld transects. Leopard tortoise mortalities were greatest along electric fences (56 % of mortalities), even though these comprised only 4% of fences in the study. By comparison, most angulate tortoises (Chersina angulata) died after becoming wedged in mesh fences. The distribution and abundance of fence types along 2200 km of roads was used to extrapolate the impacts of different fence types on tortoises in the southeastern Karoo, South Africa. A survey of land-use types indicated that game farms were more likely to be associated with the presence of electric fences. Regulations are needed to limit mortality of vulnerable species (tortoises, pangolins) on electric fences by setting a minimum strand height and ‘escape’ periods implemented through randomized off times or thermostatic switches.

Home range and movement of desert tortoises Gopherus agassizii in the Mojave Desert of California, USA

Radio telemetry of 29 desert tortoises Gopherus agassizii in 2000 and 60 in 2001 at 4 sites in the Mojave Desert of California, USA, revealed that males had larger home ranges and moved greater distances than females, but that tortoises at sites with more rainfall did not always have larger home ranges or move greater distances. The Ivanpah Valley received more rainfall than the Fort Irwin area, Superior Valley, and Fremont, but differences between home range size and rain- fall were not consistent. Within the Ivanpah Valley, the plot at the highest elevation received more rainfall than the lower plots. However, within the Ivanpah Valley, tortoises at the 3 locations did not differ in home range and movement. In the wetter year (2001), female tortoises moved greater dis- tances each day at Ivanpah than female tortoises at Superior and Fremont, which were drier sites. Males moved farther per day than females in both years. In 2001, female tortoises in the Ivanpah Val- ley used more burrows than tortoises at Fremont and Superior, but similar numbers as tortoises at Fort Irwin. There was no mortality of tortoises in 2000 and a 5% mortality in 2001.

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

Translocation could be used as a tool in conservation of the threatened Mojave Desert Tortoise ( Gopherus agassizii) by moving individuals from harm’s way and into areas where they could contribute to conservation of the species. Numerous factors may affect the success of translocations, including the conditions experienced by tortoises in holding facilities while awaiting translocation. The tortoises available for our translocation study had been provided supplemental water during their years spent in a captive holding facility, potentially 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.

Managing a subsidized predator population: reducing common raven predation on desert tortoises.

Human communities often are an inadvertent source of food, water, and other resources to native species of wildlife. Because these resources are more stable and predictable than those in a natural environment, animals that subsist on them are able to increase in numbers and expand their range, much to the detriment of their competitors and species they prey upon. In the Mojave Desert, common ravens (Corvus corax) have benefited from human-provided resources to increase in population size precipitously in recent years. This trend has caused concern because ravens prey on juvenile desert tortoises (Gopherus agassizi), a federally threatened species. In this paper, I discuss management strategies to reduce raven predation on desert tortoises. The recommendations fall into three categories: (1) managing raven populations by reducing access to anthropogenic resources; (2) removing offending ravens or other birds in specially targeted tortoise management zones; and (3) continuing research on raven ecology, raven behavior, and methods of reducing raven predation on tortoises. I also recommend approaching the problem within an adaptive management framework: management efforts should first be employed as scientific experiments--with replicates and controls--to yield an unbiased assessment of their effectiveness. Furthermore, these strategies should be implemented in concert with actions that reduce other causes of desert tortoise mortality to aid the long-term recovery of their populations. Overall, the approaches outlined in this paper are widely applicable to the management of subsidized predators, particularly where they present a threat to a declining species of prey.

Swine Flu or 1918 Pandemic? Upper Respiratory Tract Disease and the Sudden Mortality of Gopher Tortoises (Gopherus polyphemus) on a Protected Habitat in Florida

Although Upper Respiratory Tract Disease (URTD) has been recognized as a potentially serious problem threatening the viability of gopher tortoises, little is known about the impact of this disease on tortoise populations in the wild, and some researchers regard the disease as relatively benign. We monitored the impact of URTD on gopher tortoises at the Kennedy Space Center, Florida, and found a striking increase in the proportion of tortoises showing signs of URTD between 1995–2000. We also documented a sudden increase in the number of tortoises found dead at the site, starting in 1998 and continuing through 2001. Based on condition and position of dead tortoises, we strongly suspect that URTD was the cause of death. Sex ratios and body sizes of tortoises found dead were not distinguishable from samples of living tortoises, indicating that mortality was not confined to a single gender or age class. Combined with recent reports of large-scale mortality of tortoises from other sites in Florida, we suggest that URTD is not benign but may instead have a substantial impact on tortoise populations. If so, the “protected lands paradigm” that many resource managers rely on to conserve tortoise populations may be violated, suggesting that more active management measures are needed.

The rise and fall of the Aldabran giant tortoise population

At the end of the 19th century, after prolonged and extensive harvesting, indigenous giant tortoises had been eliminated from all islands in the Indian Ocean, except Aldabra atoll, where only a few survived. With greatly reduced levels of exploitation during the 20th century, the population recovered to a revised estimated total of 129,000 in 1973-1974, when the first sample census was conducted. A repeat census in 1997 revealed a highly significant reduction in numbers over the past 24 years to an estimated total of 100,000. The great majority of tortoises are still found at relatively high density in south-eastern Grande Terre, where the number of animals has declined by more than one-third. In contrast, low-density subpopulations on Malabar and Picard have almost doubled in size, but they represent less than 5% of the total population. Corroborative evidence for the crash in the Grande Terre subpopulation comes from two independent observations: a significant increase in tortoise mortality; and a significant decline in tortoise counts on long-term population monitoring transects. These population changes are attributed to natural population regulatory mechanisms, exacerbated by low rainfall years in the period 1980-1997, including two consecutive years of below average rainfall in 1995-1996 and 1996-1997.

Conservation measures for a population of Hermann's tortoise Testudo hermanni in southern France bisected by a major highway

Between May 1989 and October 1990 a highway was constructed through the core area of one of the largest French populations of Testudo hermanni, a species seriously threatened by habitat loss and habitat fragmentation. Two general strategies were used to alleviate negative impacts of the highway on the tortoise population: first, 300 tortoises, that were directly affected by the highway construction, were temporarily maintained in outdoor enclosures and relocated after construction was completed; secondly, attempts were made to reduce traffic impacts on the tortoise population, including the use of fences to keep tortoises off the road and the construction of culverts and a tunnel under the road to provide for movements of animals between the separated habitat areas. The short-term outcome of this conservation exercise was a success: the annual survival rate of 78% observed in reintroduced tortoises was comparable to published results of translocation of other tortoise species into unfamiliar habitat; traffic mortality of tortoises in the 4 years following highway construction was low and mark-recapture results indicate a stable adult population and the use of the culverts and the tunnel by tortoises to cross the road.

Mortality in imported tortoises ( Testudo graeca and T. hermanni) in the United Kingdom

Concurrent surveys of the mortality of tortoises, after purchase from pet shops, were undertaken during the periods May 1982 to May 1986 and May 1983 to May 1986. The first survey involved 499 Testudo graeca ibera and the second 106 Testudo hermanni hermanni. By the end of the survey periods 91·8% of the T. graeca were dead and 86·8% of the T. hermanni. A yearly mortality rate of between 23% and 29% is much greater than would be expected in a stable wild population. Problems associated with hibernation accounted for 84·5% of deaths. On the basis of this survey the mass importation of tortoises, into the United Kingdom, cannot be justified.

Mortality of mediterranean tortoises ( Testudo graeca and Testudo hermanni) in pet shops prior to sale

The mortality of tortoises in pet shops during 1982 and 1983 was calculated from records maintained as required under section 6 of the Endangered Species (Import and Export) Act 1976. The mean mortality rate in 1982 was 4·2% and 2·8% in 1983. Mortality was related to the number of tortoises delivered and sold as well as to poor conditions in the temporary accommodation used to house tortoises prior to sale. The mortality rate was independent of the time the tortoises spent in the shop before sale.

The tortoise trade — Mortality in transport: An analysis of 21 years of importations into the United Kingdom

The mortality of tortoises during transport, from the Mediterranean area to the United Kingdom, was assessed from importers' records and pet shop visits. The in-transit mortality rate was very low (<1%) during air transport and in long-distance lorries fitted with controlled environment facilities. In comparison with other species transported around the world for the pet trade, the in-transit mortality of tortoises is very low.

Features of tortoise mortality and decomposition on Aldabra

Apart from predation on tortoise eggs and young tortoises by crabs and birds, the Aldabran giant tortoise population is virtually unaffected by predators. The decomposition of a series of tortoise bodies, with known dates of death, was monitored for periods up to 18 months. The rate of carapace disintegration provides a useful means of introducing a temporal component to the analysis of mortality data.

The Indian Ocean giant tortoise Testudo gigantea on Aldabra

The Indian Ocean giant tortoise survives on Aldabra, an atoll north‐west of Madagascar. The Bristol Seychelles Expedition estimated the total numbers as 33,000 during visits in 1964 and 1965. Growth and movements were recorded during marking experiments. The growth rate with size is plotted, the time scale being derived from the number of rings on the shields of the shell; and the growth curve is compared with that for captive tortoises.Variation in many characters of supposed taxonomic value is explained as the influence of environmental factors on the normal growth pattern, and of non‐adaptive differences expressed during adult life. The present separation of north and south Aldabra, and Seychelles forms is not supported.An explanation is suggested for the uniformity of shape among tortoises.Observations were made on the feeding, diurnal movements and mortality of tortoises on Aldabra.