Christopher L. Jenkins

LIMITATIONS OF REGULATED “BUFFER ZONES” FOR THE CONSERVATION OF MARBLED SALAMANDERS

Most amphibians that breed in seasonal wetlands are predominantly terrestrial animals that require “upland” habitats for the majority of their life cycles. However, wetland regulations aimed partially at protecting wildlife values are often limited to the wetland basins and small terrestrial “buffer zones” that typically extend 30 m or less from the wetland edge. In this study, we assessed whether a common buffer zone (i.e., 30 m) is sufficient for the conservation of marbled salamanders (Ambystoma opacum). We installed and monitored two concentric and continuous drift fence arrays (3 m and 30 m from the pond margin) around each of three seasonal ponds in western Massachusetts, USA. We quantified the numbers and percentages of breeding adults and emerging juvenile salamanders that immigrated from and/or emigrated beyond the 30-m fences. In addition, we recorded incidental year-of-emergence captures of juveniles at more distant drift fences that were in place for a broader study. Of the breeding adults captured immigrating to the basins at 3-m fences, 84–96% were first captured at 30-m fences, and corrections for capture probabilities suggested that nearly 100% of these individuals originated beyond 30 m from their breeding sites. Of the newly emerging juveniles captured emigrating from the basins at 3-m fences, 58–85% were subsequently captured at 30-m fences and 284 juvenile captures were recorded at distances between 111 and 1,230 m (median = 269.2 m) from natal ponds. Our findings highlight the dramatic limitations of existing wetland regulations with regard to upland habitat use by mole salamanders (family Ambystomatidae) and the need to approach conservation of these animals both at broader scales and with more comprehensive and innovative strategies.

Orientation of movements and habitat selection in a spatially structured population of Marbled Salamanders (Ambystoma opacum)

Abstract Most studies on orientation of movements of pond-breeding salamanders have considered only a single local population (or breeding pond) during ≥1 yr, or multiple populations during a single year. We quantified migratory patterns of Marbled Salamanders at nine breeding ponds during 5 yr in western Massachusetts. Based on captures at drift fences, movements were nonuniform at all breeding ponds. In addition, the direction of orientation differed among breeding ponds and changed slightly across years. Within ponds, orientation of adults and juveniles differed significantly in 52% of comparisons, and adult movements were more directionally concentrated than those of juveniles. In addition, migrating salamanders shifted slightly the orientation of their movements as they traveled into uplands, suggesting that migration routes are spatially complex and that determination of migration “corridors” based on concentrated captures at the pond periphery may be misleading. Although salamanders used migration routes with higher canopy cover, our models did not explain a large portion of the variation in orientation, and protecting areas of high canopy cover alone may not be sufficient as a protection strategy. Our results suggest that movement routes, though perhaps concentrated in the short term, are unpredictable in the long term. Thus, we can offer little evidence that distinct corridors can be identified and protected that would be used consistently over time by migrating or dispersing Marbled Salamanders. Consequently, until we better understand mechanisms governing movements in this species, a conservative conservation strategy would require protecting broad terrestrial areas around breeding sites.

The role of the bandwidth matrix in influencing kernel home range estimates for snakes using VHF telemetry data

Abstract Context. Despite the diversity of available home range estimators, no single method performs equally well in all circumstances. It is therefore important to understand how different estimators perform for data collected under diverse conditions. Kernel density estimation is a popular approach for home range estimation. While many studies have evaluated different kernel bandwidth selectors, few studies have compared different formulations of the bandwidth matrix using wildlife telemetry data. Additionally, few studies have compared the performance of kernel bandwidth selectors using VHF radio-telemetry data from small-bodied taxa. Aims. In this study, we used eight different combinations of bandwidth selectors and matrices to evaluate their ability to meet several criteria that could be potentially used to select a home range estimator. Methods. We used handheld VHF telemetry data from two species of snake displaying non-migratory and migratory movement patterns. We used subsampling to estimate each estimator’s sensitivity to sampling duration and fix rate and compared home range size, the number of disjunct volume contours and the proportion of telemetry fixes not included in those contours among estimators. Key Results. We found marked differences among bandwidth selectors with regards to our criteria but comparatively little difference among bandwidth matrices for a given bandwidth selector. Least-squares cross-validation bandwidths exhibited near-universal convergence failure whereas likelihood cross-validation bandwidths showed high sensitivity to sampling duration and fix rate. The reference, plug-in and smoothed cross-validation bandwidths were more robust to variation in sampling intensity, with the former consistently producing the largest estimates of home range size. Conclusions. Our study illustrates the performance of multiple kernel bandwidth estimators for estimating home ranges with datasets typical of many small-bodied taxa. The reference and plug-in bandwidths with an unconstrained bandwidth matrix generally had the best performance. However, our study concurs with earlier studies indicating that no single home range estimator performs equally well in all circumstances. Implications. Although we did not find strong differences between bandwidth matrices, we encourage the use of unconstrained matrices because of their greater flexibility in smoothing data not parallel to the coordinate axes. We also encourage researchers to select an estimator suited to their study objectives and the life history of their study organism.

Emigration Orientation Of Juvenile Pond-breeding Amphibians In Western Massachusetts

Abstract We studied the emigration of juvenile age-class individuals of four species of pond-breeding amphibians at 14 seasonal ponds over four consecutive years in western Massachusetts. Emigration orientation of each species was non-uniform for the majority of pond-years examined. While orientation was decidedly non-uniform in most individual pond-years, combining data from successive years led to a more uniform distribution for each of the study species, although in no case did it actually become statistically uniform. Additionally, while the exact orientation of each species at each pond differed among years in almost all cases, there were some directions with consistently greater than or less than expected use across years for all ponds. Similarly, despite overall differences in orientation of individuals among ponds for a particular species, or among species at a particular pond, there were some consistent directional biases (positive and negative) across ponds and across species. Overall, our results suggest that while there are some consistent patterns in emigration among years, species, and ponds, variability in orientation over time and space is the norm. Thus, there is a need to acquire data over several years and several ponds before reaching conclusions regarding orientation patterns and making informed conservation decisions.

The Influence of Sex and Season on Conspecific Spatial Overlap in a Large, Actively-Foraging Colubrid Snake.

Understanding the factors influencing the degree of spatial overlap among conspecifics is important for understanding multiple ecological processes. Compared to terrestrial carnivores, relatively little is known about the factors influencing conspecific spatial overlap in snakes, although across snake taxa there appears to be substantial variation in conspecific spatial overlap. In this study, we described conspecific spatial overlap of eastern indigo snakes (Drymarchon couperi) in peninsular Florida and examined how conspecific spatial overlap varied by sex and season (breeding season vs. non-breeding season). We calculated multiple indices of spatial overlap using 6- and 3-month utilization distributions (UD) of dyads of simultaneously adjacent telemetered snakes. We also measured conspecific UD density values at each telemetry fix and modeled the distribution of those values as a function of overlap type, sex, and season using generalized Pareto distributions. Home range overlap between males and females was significantly greater than overlap between individuals of the same sex and male home ranges often completely contained female home ranges. Male home ranges overlapped little during both seasons, whereas females had higher levels of overlap during the non-breeding season. The spatial patterns observed in our study are consistent with those seen in many mammalian carnivores, in which low male-male overlap and high inter-sexual overlap provides males with greater access to females. We encourage additional research on the influence of prey availability on conspecific spatial overlap in snakes as well as the behavioral mechanisms responsible for maintaining the low levels of overlap we observed.

Multi-level, multi-scale habitat selection by a wide-ranging, federally threatened snake

ContextAlthough multi-scale approaches are commonly used to assess wildlife-habitat relationships, few studies have examined selection at multiple spatial scales within different hierarchical levels/orders of selection [sensu Johnson’s (1980) orders of selection]. Failure to account for multi-scale relationships within a single level of selection may lead to misleading inferences and predictions.ObjectivesWe examined habitat selection of the federally threatened eastern indigo snake (Drymarchon couperi) in peninsular Florida at the level of the home range (Level II selection) and individual telemetry location (Level III selection) to identify influential habitat covariates and predict relative probability of selection.MethodsWithin each level, we identified the characteristic scale for each habitat covariate to create multi-scale resource selection functions. We used home range selection functions to model Level II selection and paired logistic regression to model Level III selection.ResultsAt both levels, EIS selected undeveloped upland land covers and habitat edges while avoiding urban land covers. Selection was generally strongest at the finest scales with the exception of Level II urban edge which was avoided at a broad scale indicating avoidance of urbanized land covers rather than urban edge per se.ConclusionsOur study illustrates how characteristic scales may vary within a single level of selection and demonstrates the utility of multi-level, scale-optimized habitat selection analyses. We emphasize the importance of maintaining large mosaics of natural habitats for eastern indigo snake conservation.

Occupancy of Potential Overwintering Habitat on Protected Lands by Two Imperiled Snake Species in the Coastal Plain of the Southeastern United States

Abstract Eastern Indigo Snakes (EIS, Drymarchon couperi) and Eastern Diamondbacked Rattlesnakes (EDB, Crotalus adamanteus) are species of conservation concern, in large part attributable to anthropogenic landscape changes within the southeastern Coastal Plain of North America. Both species use Gopher Tortoise (Gopherus polyphemus) burrows on xeric sandhills for winter retreat sites. Protected lands play an important role in the conservation of threatened species by offering the potential to conserve potentially limiting resources such as sandhills. We surveyed 40 randomly selected xeric sandhills containing Gopher Tortoise burrows on protected lands throughout the Lower Altamaha River Watershed in southern Georgia using visual encounter surveys over three winters (November through March). We used single-season occupancy models to relate detection and occupancy rates to survey- and site-specific covariates collected at both the sandhill- and landscape-scale. Eastern Indigo Snake occupancy was positively related to the number of Gopher Tortoise burrows and the amount of surrounding sandhill habitat. In contrast, EDB occupancy was not associated with any of the covariates we considered, perhaps because EDB/EIS use a greater diversity of winter retreat sites. Detection of EIS was higher than EDB (0.40 vs. 0.22) and most influenced by air temperature, whereas EDB detection was most influenced by survey date. Our study provides previously lacking population-level detection rates and habitat associations for EIS and corroborates the previously noted importance of Gopher Tortoise burrows as overwintering retreat sites. Our study also illustrates the potential shortcomings of monitoring multiple species using survey methodologies designed for a single species.