Brad C. Timm

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.

Emigration Timing of Juvenile Pond-breeding Amphibians in Western Massachusetts

Abstract Understanding the timing of movement events of pond-breeding amphibians to and from breeding and natal ponds, respectively, is essential to implementing effective conservation and monitoring strategies for this group of vertebrates. In this study, we assessed the emigration timing of newly metamorphosed juveniles of four species of pond-breeding amphibians (Ambystoma maculatum, Ambystoma opacum, Notophthalmus viridescens, and Rana sylvatica) in western Massachusetts from data collected at 14 seasonal ponds during four consecutive years (2000–2003). Results identified emigration “windows” for juveniles of each species during each year and for all years pooled. Additionally, analyses identified considerable intraspecific variation in the timing of emigration among ponds and years for at least three of the four study species. Our results are directly applicable to management strategies (e.g., road-closures) aimed at minimizing human-related impacts (e.g., road mortality) on populations of pond-breeding amphibians, as well as to mitigation strategies (e.g., maintaining engineered wetlands with an appropriate hydroperiod length) employed in cases of direct habitat loss.

Multi-scale Mexican spotted owl (Strix occidentalis lucida) nest/roost habitat selection in Arizona and a comparison with single-scale modeling results

ContextOrganisms commonly respond to their environment across a range of scales, however many habitat selection studies still conduct selection analyses using a single-scale framework. The adoption of multi-scale modeling frameworks in habitat selection studies can improve the effectiveness of these studies and provide greater insights into scale-dependent relationships between species and specific habitat components.ObjectivesOur study assessed multi-scale nest/roost habitat selection of the federally “Threatened” Mexican spotted owl (Strix occidentalis lucida) in northern Arizona, USA in an effort to provide improved conservation and management strategies for this subspecies.MethodsWe conducted multi-scale habitat modeling to assess habitat selection by Mexican spotted owls using survey data collected by the USFS. Each selected covariate was included in multi-scale models at their “characteristic scale” and we used an all-subsets approach and model selection framework to assess habitat selection.ResultsThe “characteristic scale” identified for each covariate varied considerably among covariates and results from multi-scale models indicated that percent canopy cover and slope were the most important covariates with respect to habitat selection by Mexican spotted owls. Multi-scale models consistently outperformed their analogous single-scale counterparts with respect to the proportion of deviance explained and model predictive performance.ConclusionsEfficacy of future habitat selection studies will benefit by taking a multi-scale approach. In addition to potentially providing increased explanatory power and predictive capacity, multi-scale habitat models enhance our understanding of the scales at which species respond to their environment, which is critical knowledge required to implement effective conservation and management strategies.

Survival and Breeding Frequency in Marbled Salamanders (Ambystoma opacum): Implications for Spatio-temporal Population Dynamics

Abstract Despite known population-level sensitivity to adult vital rates, there is a shortage of robust estimates of adult survival and breeding frequency for pond-breeding amphibians. Evaluating the applicability of metapopulation principles to amphibians has also been constrained by the lack of demographic studies scaled beyond individual breeding populations. We investigate spatial and temporal demographic variability among six proximate breeding populations of Marbled Salamanders (Ambystoma opacum) in western Massachusetts, USA, focusing on the terrestrial adult life stage. Between 1999 and 2004, we captured and photographed approximately 1700 breeding adults, each between one and 12 times, at drift fences encircling breeding sites. After constructing individual capture histories from field data, we applied maximum likelihood approaches to estimate parameters for survival in the pond basins during breeding periods, survival in upland habitat during breeding and non-breeding periods, and both breeding and capture probabilities. Models selected using Akaikes Information Criteria suggested that there was moderate variability in pond survival across years, but that generally, pond and upland survival varied little among populations within years. This suggests that asynchronous variability indicative of metapopulation dynamics is unlikely to be significant in the adult stage, at least among nearby populations in similar upland forests. An integrated measure of annual survival was 0.66 (SE = 0.02) for males and 0.62 (SE = 0.01) for females. Average breeding probabilities were very high (0.96; SE = 0.01) for males and high (0.67; SE = 0.02) for females, resulting in estimates of 2.5 and 2.0 lifetime breeding attempts, respectively. These parameter estimates will be used to develop spatially explicit population models to guide conservation and forest management strategies for A. opacum and other pond-breeding amphibians with similar life histories. Additional empirical work that estimates the effects of alternative management strategies on these vital rates will greatly improve the utility of these models.

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.

Upland Movement Patterns and Habitat Selection of Adult Eastern Spadefoots (Scaphiopus holbrookii) at Cape Cod National Seashore

Abstract There is a paucity of empirical results regarding many aspects of the movement ecology and upland habitat use and preferences of the Eastern Spadefoot Toad (Scaphiopus holbrookii), an ephemeral, wetland-breeding anuran that is rare throughout a number of states in the northern portion of its range. We radio-tracked 45 adult Eastern Spadefoots in a coastal dune ecosystem at Cape Cod National Seashore, Massachusetts, United States and assessed a number of attributes related to the upland movement ecology and habitat preferences of this species. The mean maximum distance that we found for each of the 19 successfully tracked individuals, immediately post-breeding from the breeding wetlands, was 130.4 ± 28.0 m with a range of 3 – 449 m. Paired logistic regression results indicated that individuals selected areas closer to deciduous shrub edges and areas with greater percent cover of 1) ground-running pitch pine (Pinus rigida) branches at a 1-m scale, 2) deciduous shrubs at a 1-m scale, and 3) reindeer lichen (Cladonia sp.) at a 5-m scale compared to randomly selected locations. We recorded surface activity during 22/24 (∼91.7%) nocturnal survey nights and during 77/127 (∼60.6%) toad-nights; the presence of rainfall was the only significant predictor (positive) of surface activity. Our results provide an assessment of upland movement patterns and habitat preferences that will help guide the development and implementation of effective conservation and management strategies for this regionally rare species.

Surface Activity and Body Temperature of Eastern Hognose Snakes (Heterodon platirhinos) at Cape Cod National Seashore, Massachusetts USA

Abstract Snakes, as ectotherms, rely heavily on environmental temperature to drive physiological processes. Activity in terrestrial snakes is influenced heavily by environmental temperature, but climatic, temporal, and ecological factors play a role as well. Understanding when and under what conditions a species is most likely to be active on the surface can be important when dealing with a cryptic species and a species that occurs at low densities. Surface activity, body temperature (Tb), and microclimatic data were collected during a study of 17 Heterodon platirhinos in an early-successional sand-dune ecosystem from 2009 to 2011 using temperature-sensitive radiotransmitters. Mean Tb (27.9°C, SE = 0.24) and Tb range (5.5–39.5°C) were similar to those reported in other studies of H. platirhinos. Females were generally more active than males, except in September when males may be searching for mates. Mixed-effects logistic regression was used to assess the relationship between snake surface activity and selected microclimatic and temporal variables. Hours postsunrise and relative humidity emerged as the top variables influencing surface activity in gravid females. Hours postsunrise and ambient air temperature emerged as the top variables influencing surface activity in males. Our data suggest that activity in H. platirhinos occurs as a function of several environmental, temporal, and ecological factors and varies on the basis of sex and reproductive class. When considering activity, future studies on terrestrial ectotherms should consider not only the relationships of sex, but of reproductive class as well.

Meta-replication reveals nonstationarity in multi-scale habitat selection of Mexican Spotted Owl

ABSTRACT Anthropogenic environmental changes are leading to habitat loss and degradation, driving many species to extinction. In this context, habitat models become increasingly important for effective species management and conservation. However, most habitat studies lack replicated study areas and do not properly address the role of nonstationarity and spatial scales in determining factors that limit species occurrence under different environmental settings. Here we provide an optimized multi-scale framework for analyzing habitat selection of the threatened Mexican Spotted Owl (Strix occidentalis lucida) between 2 meta-replicated study areas: the Sacramento Mountains, New Mexico, and the Mogollon Plateau, Arizona. The optimized scales of habitat variables strongly differed between the 2 study areas. Percent cover of mixed-conifer was more strongly associated with the relative likelihood of Mexican Spotted Owl occurrence in the Sacramento Mountains than in the Mogollon Plateau. Topographic covariates strongly explained variance in the habitat model in the Mogollon Plateau, but not in the Sacramento Mountains. Topographically constrained habitat availability may be affecting the relative likelihood of owl occurrence in the Mogollon Plateau, but not in the Sacramento Mountains. In the Sacramento Mountains, suitable habitat and owl distributions show dissimilar spatial autocorrelation patterns, indicating that the relative likelihood of occurrence may be influenced by factors in addition to habitat. Owl distribution shows a periodic spatial pattern, suggesting that the relative likelihood of owl occurrence in the Sacramento Mountains might be influenced by territoriality. Differences in habitat relationships between the 2 study areas suggest that management strategies should be tailored to local conditions. This study underscores the advantage of scale optimization and replicated studies in analyzing nonstationary habitat selection.

Fowler's Toad (Anaxyrus fowleri) Activity Patterns on a Roadway at Cape Cod National Seashore

Abstract Amphibian road mortality is a conservation concern that is receiving increased attention by the conservation community, especially given the increasing number of studies quantifying numbers of individuals that are run over by vehicles during seasonal migrations to and from breeding wetlands and during nonmigratory activity bouts on roadways. In this study we assess the activity patterns of Fowlers Toads (Anaxyrus fowleri) on an 800-m long road segment at Cape Cod National Seashore, Massachusetts, United States, over the course of an 11-wk period during the upland activity season of this species. Our results indicated that a large number of individuals were active on this road segment, even during nonrainy nights, and that some individuals spent extended periods of time on the road segment within a given night and were present on the road segment during multiple nights throughout the study duration. These findings suggest that amphibian road mortality may not be limited to seasonal migrations to and from breeding wetlands, and our results provide indirect evidence that A. fowleri individuals may be employing roadways as migration corridors, for hydro–thermo regulatory purposes, or for foraging purposes. These extended activity rates on roadways, both within and among nights, increase road-mortality risk and provide added support for conservation actions such as temporary road closure events to reduce amphibian road-mortality rates.