Gopherus Research Articles

Growth and Survival Outcomes for Immature Gopher Tortoises in Contrasting Habitats: A Test of Drone-Based Habitat Assessment.

Juvenile growth rate is a critical demographic parameter, as it shortens the time to maturity and often dictates how long individuals remain vulnerable to predation. However, developing a mechanistic understanding of the factors determining growth rates can be difficult for wild populations. The gopher tortoise (Gopherus polyphemus) is an ecosystem engineer threatened by habitat loss and deficient management of pinelands in the southeastern United States. We investigated the factors governing immature gopher tortoise growth and explored the use of drone-based imagery for habitat assessment by comparing predictive models based on ground-based plant surveys versus drone-derived data. From 2021 to 2022, we tracked and measured immature tortoises in native sandhill and human-modified, ruderal habitat in south-central Florida. Using quarterly, high-resolution drone imagery, we quantified plant cover types and vegetation indices at each occupied burrow and measured the frequency of occurrence of forage species by hand. Annual growth rates of immature tortoises in ruderal habitat were higher than those in sandhill and were the highest published for this species. Models based on drone-derived data were able to explain similar proportions of variation in growth as ground-collected measures of forage, especially during the late dry season when both types of models were most predictive. Habitat differences in forage nitrogen content were also more pronounced during this season, when dominant ground cover in ruderal habitat (bahiagrass) had much higher nitrogen content than dominant ground cover in sandhill (wiregrass). Despite concerns about potential growth-survival trade-offs, tortoises in ruderal habitat did not exhibit lower apparent survival. Our findings indicate that habitat dominated by nutritious non-native grass can provide a valuable supplement to native sandhill through the mechanism of increased growth rates due to higher forage quality. Finally, our study demonstrates that drone technology may facilitate management by providing less labor-intensive ways to assess habitat quality for this and other imperiled herbivores.

Zooarchaeological and ancient DNA identification of a non-local gopher tortoise (Gopherus polyphemus) in New Orleans, Louisiana, USA

Zooarchaeological and ancient DNA identification of a non-local gopher tortoise (Gopherus polyphemus) in New Orleans, Louisiana, USA

Social and Spatial Structure of Male-Female Interactions in Gopher Tortoises, Gopherus polyphemus

Social and Spatial Structure of Male-Female Interactions in Gopher Tortoises, Gopherus polyphemus

Development of a rapid and reliable surveillance method for Ornithodoros turicata americanus in gopher tortoise (Gopherus polyphemus) burrows in the southeastern United States.

The soft tick Ornithodoros turicata Duges (Acari: Argasidae) is a potential vector of African swine fever virus (ASFV). We evaluated the efficacy of two methods to collect soft ticks rapidly and efficiently from gopher tortoise (Gopherus polyphemus) burrows, which are ubiquitous throughout large regions of the southeastern United States and their burrows are a known microhabitat of O. turicata. Burrow vacuuming was an effective and efficient tick collection method; no tick was captured employing CO2 trapping. Using an occupancy modelling framework, we estimated that the probability of detecting ticks from an infested burrow each time a sample was taken with this method was 58% and increased with the average relative humidity. With the occupancy model, we estimated that 70% of the burrows in the study area were infested with O. turicata. Manual sifting of the burrow material yielded more ticks (6.6 individuals/sample) than using a set of three sieves (2.9 individuals/sample), yet the probability of detecting the species was not different between the two methods (Pval = 0.7). These methods can inform the development of ASF vector surveillance and outbreak response plans in areas of high risk for ASFV introduction in the region.

Annual and Lifetime Home Ranges Reveal Movement Patterns Within and Among Local Populations of Gopher Tortoises (Gopherus polyphemus)

Annual and Lifetime Home Ranges Reveal Movement Patterns Within and Among Local Populations of Gopher Tortoises (Gopherus polyphemus)

Seasonal and Diel Gopher Tortoise (Gopherus polyphemus) Activity and Burrow Use by Commensals in Coastal Beach Dune Habitat as Examined by Wildlife Cameras

Seasonal and Diel Gopher Tortoise (Gopherus polyphemus) Activity and Burrow Use by Commensals in Coastal Beach Dune Habitat as Examined by Wildlife Cameras

Gopher Tortoise (Gopherus polyphemus) Vertebrate Burrow Commensals within a Private, Working Forest Landscape

Gopher Tortoise (Gopherus polyphemus) Vertebrate Burrow Commensals within a Private, Working Forest Landscape

Unexpected effect of geographic origin on post‐translocation survival in a long‐lived reptile, the gopher tortoise

AbstractMitigation translocations move wildlife from specific areas due to conflict with humans over land use at the site. A critical decision when carrying out mitigation translocation is the acceptable distance across which animals can be moved. This decision trades off logistical expediency of unrestricted translocation with the risk of reducing translocation success due to environmental mismatch between origin and translocation site conditions. In this study, we used a large dataset of 502 individually identifiable carcasses to examine the role of geographic origin and translocation distance in the relative survival of 2822 translocated subadult and adult gopher tortoises (Gopherus polyphemus), a species experiencing large‐scale mitigation translocation, at a recipient site in the Florida panhandle, USA. We hypothesized that if climate or habitat differences between the origin and translocation site influenced survival, tortoises translocated from within the Florida panhandle would have the highest survival. To the contrary, we found that survival slightly increased with increasing climatic difference between origin and recipient site, driven by higher survival of tortoises coming from central Florida sites compared to those from the panhandle and north Florida. This suggests that environmental mismatch due to long‐distance translocation is not a main driver of mortality. These models also indicated an effect of season, with a survival advantage to tortoises translocated in the spring and late fall, relative to summer translocations, and a negative effect of initial density on survival. Finally, we also estimated the upper bound on annual survival in three well‐monitored groups to be quite low (92–95%) for several years following release, suggesting caution when considering large translocated populations to be viable without first assessing adult survival. Our unexpected results highlight the importance of investigating species‐specific sensitivities to translocation distances and indicate the limitations of assumed linear effects of translocation distance on outcomes.

Blood bacterial microbiota of the Texas tortoise, Gopherus berlandieri, in Tamaulipas, Mexico

The blood bacterial microbiota of the Texas tortoise (Gopherus berlandieri) in Tamaulipas, Mexico, was characterized by next-generation sequencing. In 2019, blood was collected from 6 free-living tortoises. DNA was extracted, the V3-V4 region of the 16S rRNA gene was amplified, and Illumina sequencing was performed. The results showed 9 phyla, 20 classes, 42 orders, 81 families, 176 genera and 299 bacterial species. Firmicutes was the most abundant phylum in the blood of G. berlandieri; this taxon has been recorded as predominant in the intestine, excrement, nasal exudates and saliva of other species of the genus Gopherus. The dominant bacterial genera were Caldalkalibacillus, Anaerobacillus, Nesterenkonia and Bacillus. These taxa have been recorded in alkaline and halophilic soils, such as those found in G. berlandieri burrows. All of these bacterial taxa can enter the bloodstream of G. berlandieri via intestinal, oral and nasal translocation. Likewise, 3 bacterial taxa (Coxiella sp., Ehrlichia sp. and Anaplasma phagocytophilum) that are transmitted by arthropod vectors, as well as the potentially pathogenic Salmonella enterica were recorded. This information is the first bacteriological reference for the blood of G. berlandieri, and is expected to be useful for health and conservation programs.

Digital skull anatomy of the Oligocene North American tortoise Stylemys nebrascensis with taxonomic comments on the species and comparisons with extant testudinids of the Gopherus–Manouria clade

The anatomy of North American tortoises is poorly understood, despite a rich fossil record from the Eocene and younger strata. Stylemys nebrascensis is a particularly noteworthy turtle in this regard, as hundreds of specimens are known from Oligocene deposits, and as this species is one of the earliest fossil turtles to have been described in the scientific literature. Since its initial description based on a shell, many specimens with more complete material have been referred to Stylemys nebrascensis. Here, we review and confirm the referral of an important historic specimen to Stylemys nebrascensis, which includes shell, non-shell postcranial, and skull material. This allows us to document unique skull features of Stylemys nebrascensis (e.g., an unusual ‘poststapedial canal’ that connects the posterior skull surface with the cavum acustico-jugulare) and to refer another well-preserved skull to the species. Based on computed-tomography scanning of these two skulls, we provide a detailed description of the cranial and mandibular osteology of Stylemys nebrascensis. Stylemys nebrascensis has a combination of plesiomorphic skull characteristics (e.g., retention of a medial jugal process) and derived traits shared with extant gopher tortoises (e.g., median premaxillary ridge) that suggest it may be a stem-representative of the gopher tortoise lineage. This supports the hypothesis that extant and fossil tortoises from North America form a geographically restricted clade that split from Asian relatives during the Paleogene.

Relationships between Spatial Biology and Physiological Ecology in the Gopher Tortoise, Gopherus polyphemus.

AbstractThe overlap between spatial and physiological ecology is generally understudied, yet both fields are fundamentally related in assessing how individuals balance limited resources. Herein, we quantified the relationships between spatial ecology using two parameters of home range (annual home range area and number of burrows used in 1 yr) and four measures of physiology that integrate stress and immunity (baseline plasma corticosterone [CORT] concentration, plasma lactate concentration, heterophil-to-lymphocyte [H∶L] ratio, and bactericidal ability [BA]) in a wild free-ranging population of the gopher tortoise (Gopherus polyphemus) to test the hypothesis that space usage is correlated with physiological state. We also used structural equation models (SEMs) to test for causative relationships between the spatial and physiological parameters. We predicted that larger home ranges would be negatively correlated with traditional biomarkers of stress and positively correlated with immunity, consistent with our hypothesis that home ranges are determined based on individual condition. Males had larger home ranges, used more burrows, and had higher baseline CORT than females. We found significant negative correlations between lactate and home range (, , ). CORT was negatively correlated with the number of burrows used in both sexes (, , , adjusted ). No correlations were observed between space use and BA or, notably, H∶L ratio. SEMs suggested that variation in the number of burrows used was a result of variation in baseline CORT. The lack of a relationship between H∶L ratio and home range suggests that home range differences are not associated with differences in chronic stress, despite the pattern between baseline CORT and number of burrows used. Instead, this study indicates that animals balance trade-offs in energetics, likely by way of baseline corticosteroid, in such a way as to maintain function across continuously variable home range strategies.

Using genomic data to estimate population structure of Gopher Tortoise (Gopherus polyphemus) populations in Southern Alabama

Using genomic data to estimate population structure of Gopher Tortoise (Gopherus polyphemus) populations in Southern Alabama

A Comparison of Vertebrate Associates of Gopher Tortoise and Nine-Banded Armadillo Burrows in South Georgia

A Comparison of Vertebrate Associates of Gopher Tortoise and Nine-Banded Armadillo Burrows in South Georgia

Culex erraticus (Diptera: Culicidae) utilizes gopher tortoise burrows for overwintering in North Central Florida.

Mosquito-borne diseases represent a significant threat to human and animal health in the United States. Several viruses, including West Nile, Saint Louis encephalitis, and Eastern equine encephalitis are endemic. In humans, the disease is typically detected during the summer months, but not during the winter months. The ability of these viruses to reemerge year after year is still not fully understood, but typically involves persistence in a reservoir host or vector during periods of low transmission. Mosquito species are known to overwinter at different life stages (adults, larvae, or eggs) in manufactured or natural sites. Gopher tortoise burrows are known to serve as refuge for many vertebrate and invertebrate species in pine savannas. In this study, we surveyed the interior of gopher tortoise burrows for overwintering mosquitoes. We identified 4 species (Anopheles crucians s.l., Culex erraticus, Mansonia dyari, and Uranotaenia sapphirina). Cx. erraticus was the most abundant, and its presence and abundance increased in winter months, implying that this species utilized gopher tortoise burrows for overwintering. Bloodfed Cx. erraticus and An. crucians s.l. females were detected. While An. crucians s.l. fed exclusively on the white-tailed deer, Cx. erraticus had a more diverse host range but fed primarily on the gopher tortoise. Tortoises and other long-lived reptiles like the American alligator have been shown to sustain high viremia following West Nile virus (WNV) and Eastern equine encephalitis virus (EEEV) infection and therefore could play a role in the maintenance of these viruses. In addition, Cx. erraticus is naturally infected with WNV and is a known bridge vector for EEEV. As such, these overwintering sites may play a role in perpetuating over-winter arboviral activity in Florida.

Effects of Gopher Tortoise (Gopherus polyphemus) Exclusion on Plant Assemblages in a Longleaf Pine Forest

Effects of Gopher Tortoise (Gopherus polyphemus) Exclusion on Plant Assemblages in a Longleaf Pine Forest

Simulation Modeling to Assess Line Transect Distance Sampling Under a Range of Translocation Scenarios

Abstract The accuracy of posttranslocation population monitoring methods is critical to assessing long-term success in translocation programs. Translocation can produce unique challenges to monitoring efforts; therefore, it is important to understand the flexibility and robustness of commonly used monitoring methods. In Florida, USA, thousands of gopher tortoises Gopherus polyphemus have been, and continue to be, translocated from development sites to permitted recipient sites. These recipient sites create a broad range of potential monitoring scenarios due to variability in soft-release strategies, habitat conditions, and population demographics. Line transect distance sampling is an effective method for monitoring natural tortoise populations, but it is currently untested for translocated populations. We therefore produced 3,024 individual-based, spatially explicit scenarios of translocated tortoise populations that differed in recipient site and tortoise population properties, based on real-world examples, literature review, and expert opinion. We virtually sampled simulated tortoise populations by using line transect distance sampling methods and built a Bayesian hierarchical model to estimate the population density for each simulation, which incorporated individual-level covariates (i.e., burrow width and burrow occupancy). Line transect distance sampling was largely appropriate for the conditions that typify gopher tortoise recipient sites, particularly when detection probability on the transect lines was greater than or equal to 0.85. Designing the layout of transects relative to the orientation of soft-release pens, to avoid possible sampling biases that lead to extreme outliers in estimates of tortoise densities, resulted in more accurate population estimates. We also suggest that use of individual-level covariates, applied using a Bayesian framework as demonstrated in our study, may improve the applicability of line transect distance sampling surveys in a variety of contexts and that simulation can be a powerful tool for assessing survey design in complex sampling situations.

Tradeoffs between timber and wildlife habitat quality increase with density in longleaf pine (Pinus palustris) plantations

Longleaf pine (Pinus palustris), a historically abundant tree species in the southeastern United States, is often planted to restore the ecologically and culturally important longleaf pine ecosystem that once covered vast acreages in the southeastern United States. Government cost-share programs that support establishment of these plantations place restrictions on planting rates to promote wildlife habitat, as greater tree planting density may reduce canopy openness and herbaceous plant cover that are critical components of habitat for priority species, including gopher tortoise (Gopherus polyphemus) and Bachman’s sparrow (Peucaea aestivalis). However, there is expressed concern among some forest managers that more open grown trees in the plantations will be of inferior timber quality with more and larger horizontal branches and associated knots. We examined how density affects dynamics and tradeoffs among understory vegetation structure and composition, longleaf pine stem form (branch density and straightness), and longleaf pine survival by sampling 73 plantations of various ages (5–25 years) and planting rates (653–2445 trees per hectare (TPH)/264–990 trees per acre (TPA)) throughout the southeastern United States. We documented a relationship between planting rate and longleaf pine stand density at time of sampling (r = 0.69, p = 0.0001) and relationships between stand density and habitat and timber quality metrics. Greater stand density resulted in lower tree diameters but greater stand basal area than lower stand density. Higher planting rates led to lower branch density and lower straightness grades than lower planting rates. Canopy openness decreased with greater stand density, and bare ground cover and herbaceous cover decreased as density and stand age at time of sampling increased. Based on our results, we suggest that lower maximum planting rates are appropriate when wildlife habitat is a program objective because lower rates result in fewer tradeoffs, as reducing planting rates slows degradation of wildlife habitat when compared with higher maximum planting rates that have only mixed benefits on timber quality.

Tortoises to acres: The relationships and movements of property and more-than-human species in road governance processes

A web of species interdependencies, movements, and relationships exist within areas targeted for development. However, these areas hosting a multitude of more-than-human beings’ liveliness that are often only viewed by decision-makers in terms of the property regimes that encompass them. This paper examines this phenomenon in a case study of the conflict between gopher tortoise (Gopherus polyphemus) conservation and the proposed Osceola Parkway Extension in Central Florida. Gopher tortoise conservation in Florida offers a window into how conservation, mitigation strategies like offsetting, the exchangeability of property interact. The paper highlights what happens when decision-makers assume a property lens to understand and mitigate for conflicts between development and more-than-human relations to the environment. Understanding the two distinct, out of sync movements – that of gopher tortoises and that of conservation properties in offsetting – demonstrates the ways a multitude of more-than-human relationships are obscured and abstracted into transactional pieces through a property lens that moves through a logic of exchangeability. This suggests more-than-human lives, mobilities, and relationships need to become more fully part of the discussions and decision-making processes surrounding development-environmental conflicts. Only then can we begin to work towards more just multispecies decisions.

The Robber Flies (Diptera: Asilidae) of Longleaf Pine Habitats on Fort Stewart, Georgia

We inventoried the robber fly (Family Asilidae) fauna of 2 distinct Pinus palustris (Longleaf Pine) habitat types (mesic pine flatwoods, xeric sandhills) on a large, fire-managed landscape (Fort Stewart) located in the Coastal Plain of southeastern Georgia. We conducted aerial-net and sweep-net surveys at 30 sites on 111 dates from October 2020 to November 2022. We also sampled hardwood and mixed pine–hardwood communities. We collected a total of 380 robber flies comprising 25 genera and 62 species. We recorded 47 species from Longleaf Pine habitats, with 42 species collected from xeric Longleaf Pine sandhills and 20 species from mesic Longleaf Pine flatwoods. Thirty-two species were found in hardwood habitats. Machimus polyphemi, a poorly known obligate commensal of Gopherus polyphemus (Gopher Tortoise) burrows, was found at 5 sites. Two species that we documented from xeric Longleaf Pine sandhills, Machimus blantoni and Efferia slossonae, represent the first state records for Georgia. An Echthodopa cf. formosa population found in mesic pine flatwoods represents a significant range extension. Also, we report Stichopogon abdominalis from Georgia for the first time.

Movement Ecology of Gopher Tortoises in a Residential Neighborhood in Southwest Florida

Gopherus polyphemus (Gopher Tortoise) is a federally listed or state threatened species throughout its range due to significant declines in its populations, largely due to habitat loss and fragmentation. Many Gopher Tortoises reside on private lands in human-impacted and urbanized areas, yet the value of these populations to the conservation of the species is unclear. We conducted a radio-telemetry study on a population of Gopher Tortoises in a residential neighborhood in Cape Coral, FL, to determine if they could be benefitting from their location within an urban environment (i.e., whether or not they are “urbanophiles”). Some findings suggested that these tortoises could exist in an urban environment. There were no confirmed mortalities among the 10 tortoises in the year-long study, though 1 male dispersed from the area and later disappeared after 6 months. The mean annual home ranges (100% MCP) were 1.19 ha (min–max: 0.39–2.71 ha) for females (n = 5) and 1.13 ha (min–max: 0.51–1.72 ha) for males (n = 4), which are comparable to home-range sizes in natural habitats. However, other findings suggested that this urban landscape limited the animals. Gopher Tortoises rarely crossed roads (5% of all movements) and avoided lots with houses and associated human structures, in favor of undeveloped lots. Efforts to sustain these animals in urban environments can start implementing management strategies that integrate greenspaces within urban landscapes as an additional approach to protect this threatened species. This study suggests that adult Gopher Tortoises are adaptable and tolerant to high levles of urbanization and human disturbance, yet the degree to which tortoises can persist over time in these landscapes needs further exploration.