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Invasive Burmese pythons are altering the ecology of southern Florida and their distribution is expanding northward. Understanding their habitat use is an important step in understanding the pathways of the invasion. This study identifies key landscape variables in predicting relative habitat suitability for pythons at the present stage of invasion through presence-only ecological niche modeling using geographical sampling bias correction. We used 2014 presence-only observations from the EDDMapS database and three landscape variables to model habitat suitability: fine-scale land cover, home range-level land cover, and distance to open freshwater or wetland. Ten geographical sampling bias correction scenarios based on road presence and sampling effort were evaluated to improve the efficacy of modeling. The best performing models treated road presence as a binary factor rather than a continuous decrease in sampling effort with distance from roads. Home range-level cover contributed the most to the final prediction, followed by proximity to water and fine-scale land cover. Estuarine habitat and freshwater wetlands were the most important variables to contribute to python habitat suitability at both the home range-level and fine-scale. Suitability was highest within 30 m of open freshwater and wetlands. This study provides quantifiable, predictive relationships between habitat types and python presence at the current stage of invasion. This knowledge can elucidate future targeted studies of python habitat use and behavior and help inform management efforts. Furthermore, it illustrates how estimates of relative habitat suitability derived from MaxEnt can be improved by both multi-scale perspectives on habitat and consideration of a variety of bias correction scenarios for selecting background points.

Nest-site selection by most turtles affects the survival of females and their offspring. Although bog turtles (Glyptemys muhlenbergii) do not typically leave their wetlands for nesting, nest-site selection can impact hatching success and hatchling survival. Between 1974 and 2012, we monitored the fates of 258 bog turtle eggs incubated in the field and 91 eggs incubated under laboratory conditions from 11 different bogs, fens, or wetland complexes in New Jersey and Pennsylvania. Laboratory-incubated eggs exhibited the greatest hatching success (81%), but we did not detect a significant difference in hatching success between nests protected with predator excluder cages (43%) and unprotected nests (33%). However, we found significantly lower predation rates in protected nests, suggesting that while predator excluder cages successfully reduced predation, other environmental factors persisted to reduce egg survival in the field. Natural hatching success was potentially reduced by poor weather conditio...

Turtles are among the most vulnerable vertebrate group to declines, extirpations, and extinctions, especially those species with specific habitat requirements. The Bog Turtle (Glyptemys muhlenbergii) is listed as federally Threatened in the United States, but the southern population of the species does not receive full habitat protection under the Endangered Species Act. To understand Bog Turtle demographics within the southern population, we applied Cormack-Jolly-Seber and multistate models in program MARK and calculated annual adult, sex-specific, and juvenile survival for intensively sampled (19–180 sampling days) Bog Turtle populations in North Carolina. The most parsimonious model indicated that adult survival remained constant over time for all populations, but was relatively low when compared to other species of turtles. Adult survival estimates varied between 0.86 and 0.94 among the sites, all below the 0.96 adult survival estimate documented for northern Bog Turtle populations. To evaluate variat...

Spotted salamanders (Ambystoma maculatum) are pond-breeding amphibians that disperse into terrestrial habitat from natal wetlands after undergoing metamorphosis, relying on small-mammal burrows and coarse woody debris for refugia. The effect of conspecifics on burrow use in juvenile salamanders is poorly understood. Determining how the presence of conspecifics influences the settlement decisions of juvenile salamanders can increase our understanding of amphibian dispersal and our ability to predict population dynamics. We conducted behavioral laboratory trials using 58 recently metamorphosed salamanders to examine how salamanders selected burrows in the presence of conspecifics. Salamanders were more likely to settle in a burrow that was occupied by a conspecific versus an unoccupied burrow. Our results indicate that juvenile salamanders may show conspecific attraction and/or trailing behavior during the dispersal phase.

Although herbaceous perennial crops are becoming a larger component of bioenergy production both in the United States and worldwide, there is growing concern that these crops pose a substantial risk of biological invasion. Miscanthus × giganteus, a sterile hybrid native to Asia, is considered an ideal biofuel crop for lands that are poorly suited for annual food crops and is currently being tested by growers. A fertile variety of M. × giganteus was developed by seed and energy companies in an effort to decrease the costs associated with planting rhizomes. No regulations have been established to manage the risk of invasion by the fertile variety. Because bioenergy production is expanding rapidly, and the few studies to quantify invasion risks in this species have addressed small spatial scales, we used a modeling approach to explore a broader domain of invasion scenarios at landscape scales. We implemented a spatially-explicit population model of fertile M. × giganteus to determine the efficacy of proposed management strategies in limiting or slowing the spread of this species. We found that fertile M. × giganteus may spread rapidly outside of field margins, and the ability of localized management strategies to curtail spread was highly sensitive to M. × giganteus first year survival and the amount of suitable habitat within the larger landscape. Commercialization of novel “bioeconomy crops”, such as fertile M. × giganteus, could increase both production and resource conservation in agriculture; however, these crops may also produce ecosystem “disservices” such as biological invasion and accompanying risks to native species. Landscape-scale modeling that allows for rapid testing of the interactions between new crop genotypes and landscape configurations will be a powerful tool for exploring the ecological risks posed by new bioeconomy crops.

Studies examining the association between life-history strategies and behavior can help inform our understanding of the fitness consequences of reproductive behaviors. Breeding migrations are common in numerous taxa and often represent an important reproductive cost. We examined body mass changes of spotted salamanders (Ambystoma maculatum) during their seasonal breeding migrations to determine the influence of breeding behaviors on reproductive costs. We sampled salamanders entering and exiting a 0.92-ha ephemeral wetland in the North Carolina Piedmont using a 400-m drift fence completely encircling the wetland. Traps were checked daily during annual breeding migrations in mid-January to early March of 2013 and 2014. The relationship between body mass changes and explanatory factors including sex, duration of stay at wetland, and distance between site entrance and exit were examined using a set of candidate linear mixed models selected a priori and compared using Akaike's information criterion. Female sa...

Movement is a fundamental process of all organisms that has strong consequences for individual fitness, gene flow, natural selection, adaptation, population persistence, metapopulation dynamics, and species distributions. Yet, a lack of understanding about how different organisms move in relation to landscape structure and resource availability may prevent full understanding of species declines and extinctions. In this perspective, we introduce the concept of movement ecology for aquatic-breeding amphibians, summarize our knowledge on amphibian movement, identify critical gaps, and provide a context for how understanding movement will help develop solutions for more effective amphibian conservation. Juvenile amphibian movement is a multi-phase process during which individuals adjust movement speed, responsiveness to habitat features, and propensity of settling based on internal state and the external environment. Our review enables future studies to place amphibian movement data into a larger explanatory context and could help guide new avenues of research. Understanding juvenile responses to habitat features during dispersal will aid in developing realistic, predictive models of amphibian movement that could be used to further conservation and management efforts such as mitigation and restoration, and will also add to theory about how movement mechanisms during dispersal impact population persistence in altered landscapes.

Behavioral strategies of natal dispersers in response to human-altered habitat have far-reaching implications for functional connectivity and local population dynamics. Spotted salamanders Ambystoma maculatum are forest-dependent, pondbreeding amphibians which metamorphose and disperse out of aquatic habitat with limited knowledge of the terrestrial habitat. We quantified the fine-scale movement behavior and search strategies of recently metamorphosed spotted salamanders in three different habitat types (field, early successional forest and forest) and at varying distances from both hard (field and forest) and soft (early successional forest and forest) edges using fluorescent powder tracking. We found that salamanders moved straighter and with fewer turns through field habitat compared with both forest and early successional habitat. Salamanders significantly oriented movement toward forest when released in the field and when released on the edge between the forest and field. We found that salamander movement in the forest and early successional forest was approximated by a correlated random walk. Based on these results, dispersing spotted salamanders exhibit strong edge-mediated behavior when differences between habitats are stark (forest and field) and can perceive forest habitat from distances of at least 10 m. These results indicate that dispersing juvenile salamanders exhibit reasonable behavioral rules when moving through habitat types of differing quality. Knowledge of these behavioral rules will improve predictions of the effects of habitat type and configuration on amphibian survival and dispersion in altered landscapes.

Context Accurate estimates of population density are a critical component of effective wildlife conservation and management. However, many snake species are so secretive that their density cannot be determined using traditional methods such as capture–mark–recapture. Thus, the status of most terrestrial snake populations remains completely unknown. Aim We developed a novel simulation-based technique for estimating density of secretive snakes that combined behavioural observations of snake road-crossing behaviour (crossing speed), effort-corrected road-survey data, and simulations of spatial movement patterns derived from radio-telemetry, without relying on mark–recapture. Methods We used radio-telemetry data to parameterise individual-based movement models that estimate the frequency with which individual snakes cross roads and used information on survey vehicle speed and snake crossing speed to determine the probability of detecting a snake, given that it crosses the road transect during a survey. Snake encounter frequencies during systematic road surveys were then interpreted in light of detection probabilities and simulation model results to estimate snake densities and to assess various factors likely to affect abundance estimates. We demonstrated the broad applicability of this approach through a case study of the imperiled southern hognose snake (Heterodon simus) in the North Carolina (USA) Sandhills. Key results We estimated that H. simus occurs at average densities of 0.17 ha–1 in the North Carolina Sandhills and explored the sensitivity of this estimate to assumptions and variation in model parameters. Conclusions Our novel method allowed us to generate the first abundance estimates for H. simus. We found that H. simus exists at low densities relative to congeners and other mid-sized snake species, raising concern that this species may not only have declined in geographic range, but may also occur at low densities or be declining in their strongholds, such as the North Carolina Sandhills. Implications We present a framework for estimating density of species that have traditionally been considered too secretive to study at the population level. This method will greatly enhance our ability to study and manage a wide variety of snake species and could be applied to other secretive wildlife species that are most frequently encountered during road surveys.

Because many species of semi-aquatic turtles have specific habitat requirements and unique life history characteristics, they are particularly vulnerable to anthropogenic habitat modification. The federally threatened Bog Turtle (Glyptemys muhlenbergii) requires specialized wetland habitats, such as bogs and fens, in the eastern United States and often occurs in isolated populations. To develop a more a detailed understanding of the habitat use, movement, and thermal biology of Bog Turtles, we radiotracked and monitored the temperatures of 11 adult Bog Turtles at an isolated Piedmont meadow bog in North Carolina from May 2007 to March 2008. We found that turtles used soft, shallow mud habitat in the bog, but moved to a streambed when the bog became dry. While in the bog, turtles were often found within or underneath woody debris. Although most turtles resided exclusively in the southern part of the bog and the stream, two male turtles made substantial over-land movements away from the bog exceedi...

Although diamondback terrapins appear to be declining throughout much of their geographic range, more information is required to evaluate population trends. Unfortunately, sampling terrapin populations is both time and labor intensive. We initiated studies to examine the efficacy of using head counts in tidal creeks as a rapid-assessment technique for monitoring terrapin populations. From 2005 to 2007, we conducted headcount surveys in conjunction with regular aquatic sampling. Head-count surveys consisted of recording the number of terrapins we observed from a boat going up (run 1) and down (run 2) tidal creeks. These surveys were conducted before aquatic sampling (i.e., low tide) as well as other times (e.g., high tide). We found the strongest positive relationship between the number of terrapins observed in run 1 combined with run 2 and the number of terrapins captured (R 2 = 0.538). We examined the effects of variables such as day of year, time of day, cloud cover, and creek location on the number of heads seen. Such models will allow effective monitoring of terrapin population trends and improve implementation of appropriate conservation measures. We recommend a refinement of head-count surveys and the involvement of citizen scientists to aid in the establishment of a range-wide monitoring program that will greatly increase survey effort while saving time and money. © Koninklijke Brill NV, Leiden, 2009

Navigational ability is a critical component of an animal's spatial ecology and may influence the invasive potential of species. Burmese pythons (Python molurus bivittatus) are apex predators invasive to South Florida. We tracked the movements of 12 adult Burmese pythons in Everglades National Park, six of which were translocated 21–36 km from their capture locations. Translocated snakes oriented movement homeward relative to the capture location, and five of six snakes returned to within 5 km of the original capture location. Translocated snakes moved straighter and faster than control snakes and displayed movement path structure indicative of oriented movement. This study provides evidence that Burmese pythons have navigational map and compass senses and has implications for predictions of spatial spread and impacts as well as our understanding of reptile cognitive abilities.