Amphibian populations worldwide are declining in response to environmental threats, including contaminants, yet our ability to study sensitive populations in their exposure and response to environmental contaminants is limited by the reliability and accuracy of non-lethal sampling methods. Mercury (Hg)—a widespread contaminant—can be transformed in freshwater systems to methylmercury (MeHg), a more bioavailable and toxic form, threatening amphibians using these habitats. We refined methodology for non-lethal sampling and Hg determination across 13 amphibian species, where we demonstrate the efficacy of toe and tail clip tissues to estimate whole-body Hg burdens by examining whether (1) the primary form of Hg (i.e., MeHg or total mercury [THg]) is consistent across tissues and taxonomic groups; (2) clipped tissues correlate with whole-body MeHg and THg concentrations, and (3) all-species or species-specific calculations are appropriate to estimate whole-body concentrations from clips. Across all taxa, MeHg was the primary form of Hg across tissues (averaging 72–78

Conservation translocations are an increasingly common and often necessary component of recovering species that have become extirpated from portions of their range. Understanding and ameliorating potential threats that reduce the likelihood of successful population establishment at recipient sites is a key component of successful translocation planning. We examined multiple potential threats, including pathogens, contaminants, and invasive species, as well as habitat suitability and food resources, to assess the feasibility of reintroducing threatened, streamobligate foothill yellow-legged frogs, Rana boylii, to Pinnacles National Park. Foothill yellow-legged frogs were extirpated from this protected area more than half a century ago. Although invasive species, disease, contaminants, food resources, and water temperatures are unlikely to inhibit foothill yellow-legged frog population establishment, potential recipient streams at Pinnacles National Park had shorter hydroperiods and much higher canopy cover than reference streams with extant foothill yellow-legged frog populations. Although the exact cause of extirpation of foothill yellow-legged frogs from Pinnacles National Park is unknown, translocations of foothill yellow-legged frogs to the park are more likely to succeed if riparian canopy cover is reduced and stream hydroperiods increased to better match those at nearby populations. Thoroughly understanding the threats to and characteristics of potential recipient sites could improve the likelihood of success of translocation outcomes in natural areas.

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.

Rio Grande Cooters (Pseudemys gorzugi) occupy the Rio Grande watershed and have among the smallest ranges of all North American freshwater turtles. Anthropogenic dewatering is considered to have caused range contractions and population declines. We sought to facilitate management recommendations by determining the extent of movement and potential associations with extrinsic cues. We conducted a GPS-enabled telemetry study from August 2015 to May 2017 on the Devils River in Texas, USA. We included Capture–Mark–Recapture data from 2011, 2014, and 2015–2018 to determine population status in conjunction with movement ecology. Turtles showed increased movement as streamflow and water depth increased. Larger movements were also made mid-year, coincident with the peak nesting season. We speculate that seasonality and increases in streamflow facilitate switches from slower, localized movement to transiting modes. We observed individual heterogeneity in transitory movements. Such movements led us to maintain our population estimate of 726 to 1219 individuals is representative of the entire Devils River. The extent of movement in P. gorzugi has been previously underestimated and long-range movements could explain observed genetic structure. Future efforts to re-establish natural flow regimes in the Rio Grande basin could potentially be the most effective management approach for this range-restricted chelonian.

Northwestern pond turtles have gained much attention in the past few decades due to dramatic population declines. We compiled data on the pond turtle?s historic occurrence within northern Golden Gate National Recreation Area (GOGA) and Point Reyes National Seashore (PORE), including recent incidental observations by U.S. Geological Survey (USGS) staff. To build on that past data and better understand current pond turtle distribution, abundance, non-native co-inhabitants, demographics, nesting behavior, and nest site characteristics, we conducted distribution surveys here from 2015?2019. We found northwestern pond turtles using visual encounter and trapping surveys at 11 sites, mostly confirming past USGS observations at those sites. However, we detected pond turtles in only 38% of sites previously identified by USGS as having pond turtles. In our surveys, pond turtles were most abundant at two Martinelli ponds along the southeastern slopes of Tomales Bay. At this location, we have an estimated population size of 94 adults (carapace length range from 68 to 300) from mark-recapture trapping surveys. This site is also the largest nesting population in the park, with annual nest abundance of 13.75 nests per year and a mean clutch size of 4.9 eggs per nest. The demographic data from the Martinelli Ponds indicates a population skewed towards larger individuals, which is consistent with other locations elsewhere in California. This population data served to identify the Martinelli Ponds population as the donor site for a GOGA pond turtle headstart project. Nesting activity in 2017?2019 occurred from late May with activity peaking in mid-June and tapering off in mid-July. Visual surveys proved to be the most effective means of finding nesting females and nests; camera traps, VHF telemetry, and PIT antenna array costed time and money while not providing the desired information. Future inventory efforts should focus on resurveying lightly surveyed sites where we were not able to find northwestern pond turtles, periodic monitoring of abundance and demographic structure of main PORE population (Martinelli Ponds), and surveillance monitoring for invasive bullfrogs and turtles. Increasing public awareness of the status of northwestern pond turtles is another key action that will play a major role in their conservation.

Integration of agroecosystems and other working landscapes with protected lands and waters is critical to the conservation of Earth's biodiversity. Rice agroecosystems support many species by providing aquatic habitat where natural wetlands have been altered or drained. In regions with long dry seasons, rice fields and associated irrigation canals provide essential habitat for wetland‐dependent species. We quantified the spatial scale and magnitude of the effect of rice growing on the growth and survival of the giant gartersnake ( Thamnophis gigas ), a threatened species that persists primarily in areas of rice agriculture in the Central Valley of California, USA. We used structural causal models to identify drought condition as a key confounder to adjust for when estimating the total effect of rice growing on demographic rates. We analyzed capture‐mark‐recapture data from 19 populations of giant gartersnakes with an integrated growth–survival model and used distance‐weighted covariates to account for the decline in influence of rice with increasing distance from our study sites. We found strong support for a positive effect of rice grown within 1.9 km of a canal on giant gartersnake growth. There was also support for a positive effect of rice on giant gartersnake survival, although the spatial scale extended out to 5 km or more. Our results demonstrate how active rice growing benefits giant gartersnakes inhabiting irrigation canals and demonstrate an approach for studying landscape effects on wildlife in agroecosystems.

Batrachochytrium dendrobatidis (Bd) is a globally distributed fungal pathogen of amphibians that has contributed to one of the largest disease-related biodiversity losses in wildlife. Bd is regularly viewed through the lens of a global wildlife epizootic because the spread of highly virulent genetic lineages has resulted in well-documented declines and extinctions of multiple amphibian species. However, the current state of Bd occurrence, host range, host impacts, and ecological drivers remains poorly understood outside of the most negatively affected amphibian species and regions. Our objective was to describe the macroecology of Bd occurrence and infection intensity on caudates (salamanders) across the United States and to compare these patterns with better-studied anurans (frogs and toads). We collected swabs from 11,183 amphibians at 609 sites from 54 species across the United States from 2015 to 2017. We analyzed the prevalence and intensity of Bd infection jointly using a Bayesian hurdle model with covariates of site-level temperature and precipitation, as well as individual characteristics and species identification. Bd was distributed widely across sites and species sampled across the spatial extent of the conterminous United States. We found that Bd prevalence and intensity were most strongly influenced by temperature in the month preceding sampling and by differences among taxon groups. We estimated that temperature had a strong and nonlinear influence on both Bd prevalence and intensity with peak infection at intermediate temperatures and lower infection at low and high temperatures. We found Caudate hosts tended to have higher prevalence than Anuran hosts and Anuran hosts tended to have higher intensity at optimal temperatures for Bd infection. Our findings suggest that Bd has an amphibian-wide host range, temperature gradients exert a strong influence on Bd, and enzootic transmission likely encompasses a much larger spatial and species distribution than previously recognized across North America.

Gaps in dispersal data limit habitat protection efforts. We sought to characterize such gaps and compare the utility of dispersal data from demographic and genetic methods in making habitat protection decisions. Here, we used a search string to retrieve dispersal studies for amphibians, reptiles, birds, and mammals. We included studies based on a set of selection criteria. We used this sample of selected studies to assess for persistence of taxonomic and geographic biases. We extracted non-effective (i.e., demographic) and effective (i.e., genetic) dispersal rates. We weighted these dispersal rates by associated sample size and standard deviation to indicate the ability to capture population-level dispersal. We then tested for variation in weighted dispersal by study type using Bayesian mixed-effects models. Amphibians were the most under-represented taxonomic group in our sample. Dispersal studies were mostly retrieved from developed nations indicating the distribution of dispersal research reflected GDP rather than the number of threatened species. The magnitude of dispersal from genetic methods exceeded demographic methods in all vertebrate groups considered in our study. Further, genetic studies consistently sampled a larger number of individuals. Thus, genetic methods may be better suited to characterize population-level dispersal. However, demographic and genetic approaches enable examination of the dispersal process at varying spatial and temporal scales and a combination of these approaches can be used to address persistent gaps in dispersal and enable land-management decisions.

Anthropogenic influences like land use and climate variability interact with natural heterogeneity to influence the persistence of stream salamanders. Using occupancy modeling in the southern Appalachian Mountains, we investigated the influence of land use, climate, and physical context (e.g., drainage area, elevation) on stream salamander occupancy, noting species, and life stage specific responses. Our results illustrate that forest loss is a better predictor of salamander occupancy than physical context (elevation) or climate. Across the gradients in this dataset, precipitation did not have a significant influence on salamander occupancy, potentially due to the observed narrow, wet gradient. Temperature had little effect on Eurycea wilderae occupancy; however, temperature negatively affected adult but not larval Desmognathus amphileucus occupancy. Spatial thermal variability in this study was larger than projected increases due to climate change, suggesting that local mechanisms (e.g., behavior or physiological plasticity) may facilitate salamander resilience to climate change. However, the negative effects of forest loss coupled with rising temperatures (e.g., increased solar radiation, warmer stream runoff) underscore the importance of riparian forests in mitigating climate stressors. Preserving forest cover is critical for maintaining stream salamander populations and may offer opportunities for maintaining resilience in the face of additional stressors like rising temperatures or drought.

The drivers of population dynamics are a primary interest of ecologists, and predicting the consequences of climate variability on wildlife populations benefits from an understanding of how weather causes variation in the vital rates of populations. Given recent and projected extremes in annual precipitation in the Sierra Nevada of California, USA, including two severe droughts, we sought to examine the role of snowpack and summer water availability on the population dynamics and potential extirpation of a meadow population of the U.S. Endangered Sierra Nevada yellow-legged frog (Rana sierrae) using a long-term capture-mark-recapture dataset. We found that snowpack and summer water availability affected both survival and recruitment probabilities. Although these variables only explained approximately 17 % of the annual variation in adult survival, they explained 81 % of the variation in recruitment into the adult population. Following two severe, extended droughts and a nearby wildfire, the population consisted of 20 or fewer individuals with >95 % certainty, and 10 or fewer individuals with 64 % certainty. If realized, increased precipitation volatility and extended droughts likely present an additional threat to some meadow populations of this endangered frog.

Conservation translocations and reintroductions are widely used to improve conservation outcomes for declining species. Reintroductions are unlikely to be successful if the threats that led to the extirpation of the focal species, such as non-native predators, have not been ameliorated. The non-native brown treesnake (Boiga irregularis) was introduced to Guam in the mid-20th century and has devastated the native lizard fauna of this Pacific Island. Native lizard populations persist on small islands near Guam and could act as sources for reintroductions. Recently, trapping methods have been shown to greatly reduce the density of brown treesnakes, raising the possibility that native lizards could be reintroduced where brown treesnake abundance is controlled. Here we developed demographic models for four lizard species present on Guam to assess their validity as a trial for reintroducing species to meet native species recovery goals. These four species vary in their size, activity, and susceptibility to predation by brown treesnakes. We used periodic matrix models to simulate changes in lizard vital rates driven by the wet-dry seasonal cycle found on Guam. We found that the release of 60 individuals of each species was likely to result in successful reintroduction outcomes provided adult survival in the wild is similar to rates estimated based on life history parameters. Demographic models can be used to forecast reintroduction outcomes, including predicting the probability of success and evaluating causes of failure in the event that populations do not establish.

We describe the results of long-term population monitoring of the island night lizard Xantusia riversiana on San Nicolas Island, California, following the species' removal from the U.S. Endangered Species list in 2014. Monitoring activities were carried out from October 2014 through November 2023, but we also incorporate data from earlier work dating back to 1993. Because of habitat loss on the western part of the island, the island night lizard is almost entirely confined to the island's eastern half. The species' distribution remains largely the same since studies in the 1990s, though small increases in distribution were noted at the island's west end. Numbers at most long-term monitoring sites appeared to show a slight decrease associated with a multi-year drought, with numbers returning to previous levels by the end of the monitoring period. Models fit to counts of newly recruited lizards suggested a positive association between winter precipitation and abundance; however, we found a simpler model including constant abundance throughout the study to be more parsimonious. Two monitoring sites showed marked decreases in numbers, with one site declining to zero following infestation of the area by non-native Argentine ants Linepithema humile. The island's vegetation and natural communities continue to gradually recover from a century of overgrazing by sheep and the widespread introduction of aggressive non-native plants. Habitat restoration efforts by U.S. Navy natural resources staff on the island may lead to increasing population numbers and genetic connectivity, but persistent threats remain for the island night lizard on San Nicolas Island.

Disease, alone or combined with other stressors such as habitat loss and contaminants, affects wildlife populations worldwide. However, interactions among stressors and how they affect demography and populations remain poorly understood. The amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd) is a sometimes-lethal pathogen linked with population declines and extirpations of amphibians globally. Laboratory evidence shows ubiquitous contaminants like methylmercury (MeHg) can reduce vigor and survival of amphibians, but population-level effects remain unclear. We used non-lethal sampling to assess how Bd and MeHg affected survival of juvenile and adult amphibians in 20 populations across the USA. Survival of several species declined with increasing Bd loads, including some species previously considered resistant to Bd (e.g., eastern newt [Notophthalmus viridescens]). Although our sampling for MeHg was less intensive than for Bd, we found MeHg can both directly reduce survival and synergistically magnify the effects of Bd infection. For a population of foothill yellow-legged frogs (Rana boylii), the estimated reduction in survival from MeHg exceeded that from Bd. Although effects varied widely among populations and species, our results help clarify the potential for synergistic effects of disease and contaminants and emphasize the complexity of identifying and quantifying the population-level effects of interactions among stressors.

Estimating individual survival is critical for understanding wildlife population dynamics and engaging effectively in conservation efforts. Individual survival rates can be difficult to estimate for secretive animals such as snakes, making demographic studies of snakes rare. Ages are difficult to estimate for snakes, but survival estimates that are based on body size eliminate the need for age data. However, modeling a time-varying individual covariate such as body size is difficult when individuals are rarely recaptured. We conducted a capture-mark-recapture study of Alameda Whipsnakes (Masticophis lateralis euryxanthus), a species listed as threatened at both the state and federal levels in California. To determine how whipsnake survival varies with body size, we used a growth model in a Bayesian framework to fill in missing individual covariate values when animals were not encountered and then used these values in a hierarchical capture-mark-recapture model estimating survival based on body size. We observed a strong relationship between body size and survival. Apparent survival increased dramatically from the smallest sizes to a snout-vent-length of approximately 450 mm before leveling out as intermediate-tomaximum body sizes were reached. We estimated annual apparent survival for adults as 53% for females and 59% for males. Our study provides the first survival estimates for M. lateralis euryxanthus, which represent foundational demographic variables for understanding population dynamics in this threatened species.

Species with extensive geographical ranges pose special challenges to assessing drivers of wildlife disease, necessitating collaborative and large-scale analyses. The imperilled foothill yellow-legged frog (Rana boylii) inhabits a wide geographical range and variable conditions in rivers of California and Oregon (USA), and is considered threatened by the pathogen Batrachochytrium dendrobatidis (Bd). To assess drivers of Bd infections over time and space, we compiled over 2000 datapoints from R. boylii museum specimens (collected 1897–2005) and field samples (2005–2021) spanning 9° of latitude. We observed a south-to-north spread of Bd detections beginning in the 1940s and increase in prevalence from the 1940s to 1970s, coinciding with extirpation from southern latitudes. We detected eight high-prevalence geographical clusters through time that span the species' geographical range. Field-sampled male R. boylii exhibited the highest prevalence, and juveniles sampled in autumn exhibited the highest loads. Bd infection risk was highest in lower elevation rain-dominated watersheds, and with cool temperatures and low stream-flow conditions at the end of the dry season. Through a holistic assessment of relationships between infection risk, geographical context and time, we identify the locations and time periods where Bd mitigation and monitoring will be critical for conservation of this imperilled species.

In the first range-wide population viability model for the northwestern and southwestern pond turtles (Actinemys marmorata and Actinemys pallida, respectively), a stage-based population projection matrix was assembled with 3 life stages: hatchling, juvenile, and adult. Vital rates were defined using biologically appropriate statistical distributions, with additional parametric uncertainty included for the adult survival parameter. A triple-loop stochastic simulation model was built around a population viability analysis to project pond turtle populations into the future. Initial abundance was calculated using available historical presence data and remotely sensed landscape condition metrics. A negative binomial regression was used to predict the relationship between abundance, habitat area, and human modification. Populations of pond turtles are dominated by adult individuals, so we applied a nonstable stage distribution to initial abundance values. Initial abundances of analysis units were variable across the species' ranges, but all populations declined precipitously in the population projections. By the end of the century, the mean range-wide probability of extinction was 44.3% for the northwestern species and 57.8% for the southwestern species. Consistent with other long-lived chelonian species, population growth rate was most sensitive to adult survival, indicating that where possible, conservation efforts focusing on increasing or maintaining adult survival would benefit the species. Elasticity analysis indicated a bet-hedging life history strategy where long- term reproductive output is maximized through longevity, small clutches, and frequent reproductive bouts in the face of highly variable juvenile survival. The population dynamics presented here indicate that efforts to bolster adult survival would be most beneficial in terms of long- term population viability, which can inform targeted research and management. The feasibility of such efforts is an important consideration in conservation management for these longlived species.

Knowledge of species distributions is critical for conservation, but surveying for rare, understudied species presents many challenges. A two-phase occupancy study can increase knowledge gained from early occupancy studies of a species by quickly using data from the first survey period to revise the study design for a second period. The Temblor legless lizard Anniella alexanderae is a recently described fossorial species found in the southwestern San Joaquin Valley, California, and its status is currently under review by state and federal wildlife agencies. As a fossorial species that is rarely surface active, Temblor legless lizards might be unavailable for detection at certain times of year or under inhospitable conditions (e.g., hot, dry weather), indicating the importance of accounting for false-negative surveys when determining its distribution. We used a multiscale occupancy model to disentangle detection probability, availability for detection, and occupancy for Temblor legless lizards. Focusing our effort from mid-February to mid-April when temperatures are mild and soil moisture is expected to be higher near the surface, we surveyed a total of 89 sites in 2022 (n = 60) and 2023 (n = 68) and detected Temblor legless lizards at 12 sites, including 5 new localities. Detection probability was positively related to temperature during our late winter-early spring survey period, and availability for detection was consistently high with minimal fluctuation within each year. Nevertheless, repeated surveys with nondetection can increase confidence that this fossorial lizard does not occur at a site. Temblor legless lizards were more likely to occur at sites near ephemeral streams and in areas without high clay soil content, but more investigation could help to discern drivers of occurrence. Our study provides valuable information for optimizing surveys for Temblor legless lizards and suggests promising directions for future research on this species' ecology.