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At least 55 records · Page 3Linked to original sources
USGS2024

Predicted occurrence of Eastern Newts (Notophthalmus viridescens viridescens) across the northeastern United States

Effective conservation is becoming more difficult as threats to wildlife increase. Natural resource managers are pressured to make difficult decisions with limited resources, and in many instances, large uncertainty. Scientists and managers tasked with the conservation of a species need tools to help guide efficient decision-making. Often, information for management decisions is insufficient. Tools that help to inform decision makers and address uncertainty are invaluable to effective conservation initiatives. The objective of our study was to create a model to best predict Eastern Newt (Notophthalmus viridescens viridescens) breeding occurrence across the northeastern United States. We estimated relationships between breeding newt field survey data and landscape-level covariates while accounting for imperfect detection. We then used those relationships to map expected newt breeding site occupancy across the northeastern United States. We find that newt breeding occupancy is inversely correlated to the amount of human influence in a landscape, highlighting a key existing threat to Eastern Newts that may be exacerbated by the introduction of novel pathogens, such as the fungal pathogen Batrachochytrium salamandrivorans.

Herpetologica↗
USGS2023

Evaluating growth rates of captive, wild, and reintroduced populations of the imperiled Eastern Indigo Snake (Drymarchon couperi)

Reintroduction of species at sites where populations have been extirpated has become a common technique in wildlife conservation. To track progress towards reintroduction success, effective postrelease monitoring is needed to document vital rates of individuals and the corresponding impact on population trajectories. We assessed growth and body size in Eastern Indigo Snakes (Drymarchon couperi) using a data set from multiple projects across the species' distribution, including free-ranging wild snakes, snakes reared in captive-breeding programs, and snakes released at two reintroduction sites. We used these data to fit a von Bertalanffy growth model in a Bayesian framework to quantify differences in growth among three broad categories of snakes (wild, captive, and reintroduced), while accounting for measurement error across various projects. We also compared changes in body mass of captive-born individuals from four captive rearing facilities. Asymptotic snout–vent length across all groups was 185 cm (95% credible interval = 177–194 cm) for males and 157 cm (95% credible interval = 153–161 cm) for females. Reintroduced snakes had a higher growth coefficient than either captive or wild snakes (e.g., captive females = 1.20 [1.06–1.35] d –1 ; wild females = 1.22 [0.95–1.49] d –1 ; reintroduced females = 1.62 [1.21–2.05] d –1 ), indicating that current captive-breeding and rearing efforts for indigo snakes produce similar or faster growth trends compared to wild populations. Furthermore, daily changes in juvenile body weight relative to body size were similar in three of the four captive rearing facilities (mean for females at Orianne Center for Indigo Conservation = 0.57 [0.48–0.65]; Zoo Atlanta = 0.55 [0.37–0.72]; Welaka National Fish Hatchery = 0.55, [0.36–0.73]; Auburn University = 0.39 [0.21–0.58]). Long-term project success for indigo snake reintroductions will depend on continuing to implement best practices in an adaptive management framework.

Herpetologica↗
USGS2024

Variation in dietary ecology of two invasive American Bullfrog (Lithobates catesbeianus) populations in Southern California

Invasive American Bullfrogs (Lithobates catesbeianus) are a threat to native species in riparian ecosystems worldwide. They are indiscriminate predators consuming both vertebrate and invertebrate prey, negatively affecting biodiversity. Documenting the diet and feeding ecology of invasive L. catesbeianus can help management agencies identify affected species and facilitate eradication efforts. We present a dietary analysis of two invasive L. catesbeianus populations over multiple breeding seasons (2016–2020), elucidating ontogenetic changes in diet and dietary differences between sexes and habitats. This is the first study to analyze dietary variation from contemporary populations of invasive L. catesbeianus occupying different watersheds in Southern California, an area where their invasion presents acute conservation challenges. Our analysis of 667 gut contents shows that adult females had more prey in their guts than adult males, even though male and female body size was not significantly different. Adults were more likely than juveniles to consume vertebrate prey, and juveniles were more likely than adults to have empty stomachs. We also found that invasive Red Swamp Crayfish (Procambarus clarkii), made up a substantial portion of the diet of adult L. catesbeianus at the site where they were present. These results provide an important ecological context for designing mitigation actions that ameliorate the impacts of invasive L. catesbeianus.

California↗
USGS2024

Postrelease survival of Eleutherodactylus coqui: Advancing managed translocations as an adaptive tool for climate-vulnerable anurans

Translocating amphibians to alternative, suitable habitat is a climate adaptation strategy aimed at minimizing the risk of extinction due to projected global warming and drying. Projected conditions could undermine their physiological performance, and thus survival and reproduction. Translocations minimize risks of extinction by increasing spatial redundancy across climate-resilient habitats, particularly for dispersal-limited species. However, outcomes of amphibian translocation attempts are poorly documented, and their effectiveness remains unclear. We released and tracked 34 Eleutherodactylus coqui to determine early postrelease survival of a control (nontranslocated) group ( n = 14) and experimental (translocated) group ( n = 20) moved 0.8 km from their capture location in west-central Puerto Rico in 2021. We defined “initial” as the first 17 d postrelease, a period during which we hypothesized that experimental individuals would have lower survival rates because they transitioned from known-familiar to novel-unfamiliar habitat. We found no evidence in the data to support our hypothesis. Daily survival rates were better explained by a model with no group effect but negatively influenced by in situ temperature. However, the effect of in situ temperature (proxy of operative temperature) was weak (95% confidence intervals overlapped 0). After 17 d, all but one of the recaptured frogs lost weight for a combined weight loss of 0.28 ± 0.13 g. However, weight loss was significantly higher in translocated frogs (0.81 ± 0.33 g). Average daily movements did not hinder survival even though experimental individuals traveled farther (～ eight times) than control ones. Our findings suggested that managed translocations have the potential to become a useful conservation tool, not an additive source of mortality. We outline challenges that remain before translocations of Eleutherodactylus species can be broadly applied.

Puerto Rico↗
USGS2025

Aggregated space use by soft-released translocated Gopher Tortoises (Gopherus polyphemus)

Translocated herpetofauna can exhibit irregular space use and movement patterns when compared with resident conspecifics. In Florida, USA, Gopher Tortoises ( Gopherus polyphemus ) are translocated throughout the state to mitigate habitat loss due to development. The postrelease space use of translocated Gopher Tortoises within soft-release pens can affect population dynamics and population monitoring efficacy, and understanding spatial patterns can aid wildlife managers with population management. We used a combination of time-lapse cameras, animal tracking devices, and burrow distribution surveys to investigate translocated tortoise space use at Eglin Air Force Base, Florida, where tortoises have been translocated since 2015. We investigated 10 soft-release pens that varied in size (4–41 ha) and shape (due to landscape configuration and existing infrastructure). Time-lapse cameras and burrow distribution surveys showed that tortoises used habitat within 20 m of soft-release pens (silt fences) significantly more than the interior of pens. In most pens, the selection of pen-edge habitat resulted in a clustering effect that lessened upon subsequent surveys, after fences were removed. Additionally, our tracking data showed mixed evidence for clustering, where three of the seven tortoises used edge area significantly more than the interior of pens. Such clustering can affect the efficacy of population survey methods while potentially having negative impacts on the health of translocatees by increasing local density.

Florida↗
USGS2025

Home range, seasonality, and the importance of canopy cover for Texas Tortoises (Gopherus berlandieri)

Texas Tortoises ( Gopherus berlandieri ) are understudied compared to federally protected congeners. Despite important early studies on the basic ecology of G. berlandieri , quantitative identification of habitat associations with specific environmental conditions has been limited. Gopherus berlandieri inhabits Tamaulipan thornscrub across its range, and coastal populations are historically associated with low-relief clay ridges with thick mesquital scrub surrounded by salt prairie grasslands. Our study examined tortoise home range size and association with canopy cover and potential ground moisture at a protected natural area in Cameron County, TX, USA. Twelve tortoises were outfitted with GPS loggers that recorded location once an hour from March 2020 to March 2022. To delineate home ranges, we estimated utilization distributions (UDs) for tortoises as autocorrelated kernel density estimates (AKDEs) at low-use (95%) and core-use (50%) levels for each tortoise. UDs were estimated for the entire study period and during seasons of sustained heat or cold to determine if tortoises used space differently across these seasons over the study period. Applying a use-availability study design, we compared canopy cover and potential mesic ground condition (i.e., precipitation flow accumulation) within each tortoise's UD (“use”) to the area within 1 day's movement around the boundary of the UD (“available”). Tortoise UD sizes were significantly different across seasons for low-use (95%) but not for core-use (50%) AKDE levels. Tortoise UDs had greater canopy cover compared to available-but-unused areas at both AKDE levels. Potential mesic ground condition did not significantly differ between available and used areas. Our study revealed that tortoises vary the size of their home ranges throughout the year, whereas areas of intensive use or occupation tended to remain remarkably stable throughout the year. In seasons of extreme weather (hot or cold), tortoises seem to seek out areas of denser canopy cover that likely serve as thermal refugia. Based on our results, effective habitat identification may best be served by ensuring that canopy cover is at least equivalent to the values reported here to ensure sufficient refugia during extreme seasonal temperatures.

Texas↗
USGS2025

Spatially explicit demographics of Mojave Desert Tortoises on a demography plot in California, USA

Obtaining reliable estimates of demographic parameters is critical to effective wildlife conservation and management. Densities of Mojave Desert Tortoises ( Gopherus agassizii ) were historically derived from capture–mark–recapture surveys on small, often strategically placed demography plots, or demographic study areas, that also provided information on demographic composition and vital rates. After protection was afforded to Desert Tortoises under the US Endangered Species Act in 1990, monitoring shifted mostly to line-distance sampling across broad areas for estimating densities of primarily adult tortoises to inform long-term population trends. However, that approach is incapable of providing data about other demographic characteristics important to population growth and viability. We surveyed a previously unsampled demography plot in the western Mojave Desert, California, USA, during 2022 and applied spatial capture–recapture (SCR) models to estimate spatially explicit Desert Tortoise density and sex-by-size class compositions. Directly accounting for spatiotemporally varying survey effort in SCR models via hazard-based adjustment reduced the estimated detection rate by 91% and increased the estimated density by 17%. Estimated spatial mean Desert Tortoise density across a 2.53-km 2 area was 18.53 tortoises/km 2 (95% confidence interval [CI] = 12.36–27.77). The SCR model–estimated size class ratio was skewed toward prereproductive tortoises (64% prereproductive; 36% adults), whereas the adult sex ratio was female biased (61% females; 39% males). Those ratios corresponded to densities of 11.86 prereproductive tortoises/km 2 (95% CI = 7.91–17.77), 4.08 adult female tortoises/km 2 (95% CI = 2.72–6.11), and 2.59 adult male tortoises/km 2 (95% CI = 1.73–3.89). Estimated tortoise density and demographic composition collectively support a high potential for population growth. Our study provides an illustrative example of using SCR models to directly estimate spatially explicit local Desert Tortoise densities and demographic composition that can be used for long-term monitoring and comparisons with other demography plots to inform conservation.

California↗
USGS2025

Occurrence and surface availability of Siskiyou Mountains Salamanders (Plethodon stormi) and Scott Bar Salamanders (P. asupak) in northern California

Estimating the distributions of cryptic species is essential for conservation, yet our understanding is hampered by animal behavior and imperfect detection. We developed and implemented a multiscale occupancy survey protocol to estimate the probability of occurrence, probability of being active on the surface, and detection probability of two range-restricted terrestrial salamanders, Scott Bar Salamanders ( Plethodon asupak ) and Siskiyou Mountains Salamanders ( P. stormi ), in interior northern California, USA. We established survey sites near locations of historical occurrence of these salamanders and surveyed each site on one to six visits in late fall 2023 and spring 2024. We compared models with different environmental variables for predicting salamander occurrence and surface activity. Much model selection uncertainty in the effects of covariates existed, but the model with most support indicated that Plethodon salamanders in interior northern California were more likely to occur at sites near recent historical occurrences that had longer growing seasons after controlling for elevation and aspect. Plethodon stormi or P. asupak surface activity was higher at night than during the day and was highest when substrates were cool and moist. Our survey protocol was successful for quantifying the effects of site and visit characteristics on P. stormi or P. asupak occurrence and availability; minor modifications will likely improve its utility for providing unbiased inference about salamander occurrence and surface activity.

California↗
USGS2004

Potential causes for amphibian declines in Puerto Rico

We monitored 11 populations of eight species of Eleutherodactylus in Puerto Rico from 1989 through 2001. We determined relative abundance of active frogs along transects established in the Caribbean National Forest (El Yunque), Carite Forest, San Lorenzo, and in the vicinity of San Juan. Three species (Eleutherodactylus karlschmidti, E. jasperi, and E. eneidae) are presumed to be extinct and eight populations of six different species of endemic Eleutherodactylus are significantly declining at elevations above 400 m. Of the many suspected causes of amphibian declines around the world, we focused on climate change and disease. Temperature and precipitation data from 1970a??2000 were analyzed to determine the general pattern of oscillations and deviations that could be correlated with amphibian declines. We examined a total of 106 tissues taken from museum specimens collected from 1961a??1978 and from live frogs in 2000. We found chytrid fungi in two species collected at El Yunque as early as 1976, this is the first report of chytrid fungus in the Caribbean. Analysis of weather data indicates a significant warming trend and an association between years with extended periods of drought and the decline of amphibians in Puerto Rico. The 1970's and 1990's, which represent the periods of amphibian extirpations and declines, were significantly drier than average. We suggest a possible synergistic interaction between drought and the pathological effect of the chytrid fungus on amphibian populations.

Puerto Rico↗