A Literature Review of the Effects of Roads on Amphibians and Reptiles and the Measures Used to Minimize Those Effects Denim M. Jochimsen1, Charles R. Peterson1, Kimberly M. Andrews2, and J. Whitfield Gibbons2 1Herpetology Laboratory Department of Biological Sciences Idaho Museum of Natural History Idaho State University Pocatello, Idaho 83209-8007 2University of Georgia Savannah River Ecology Laboratory Drawer E Aiken, SC 29801 Final Draft 11 November 2004 Idaho Fish and Game Department USDA Forest Service 0 Table of Contents Executive Summary 2 Introduction 3 Methods 4 Effects of Roads 6 Organization 6 Characteristics of Amphibians and Reptiles that Influence 8 Susceptibility to Road Effects Characteristics of Roads 11 Direct Effects: Road Mortality 17 Indirect Effects of Roads via Habitat Changes 26 Road Effects on Amphibian and Reptile Movements 30 Road Effects on Amphibian and Reptile Populations 33 Road Effects on Species Richness 41 Methods to Minimize the Ecological Effects of Roads 42 Avoidance of Ecological Impacts 43 Road-Crossing Structures 45 Case Studies 54 Recommendations 61 Acknowledgments 62 Literature Cited 62 Figure 1 7 Figure 2 18 Table 1 46 Table 2 53 1 Executive Summary Based on a literature review of over 200 references, this document addresses the adverse ecological effects of roads and traffic on amphibians and reptiles and examines methods to mitigate these effects. In this review, we consider the characteristics of the roads themselves as independent variables that potentially affect amphibians and reptiles, both directly and indirectly. Direct effects are considered to involve injury or mortality due to physical contact from vehicles or occurring during road construction. Indirect effects include habitat loss, fragmentation, and alteration of ecosystem processes at both fine and broad scales (physical, chemical, and biological). These changes may influence the behavior, survival, growth, and reproductive success of individual animals, cumulatively resulting in population-level consequences. Similarly, the summed effects on different species may influence the overall species richness and diversity in an area. Roads are significant features of most landscapes, covering about 1% of the United States and ecologically influencing an estimated 15-20% of the US land area. A variety of road characteristics needs to be considered to understand the potential effects on amphibians and reptiles and their populations, including activities involved in road construction, the type of road, the amount of traffic, the density of roads in the area of interest, the spatial distribution and environmental context of the roads, and the presence and type of road crossing structures. Additionally, the intensity of road effects is influenced by a suite of biological characteristics of amphibians and reptiles, such as complexity of habitat requirements, skin permeability, thermoregulation, vagility (i.e., tending to change location over time), speed of movement, variation in population sizes, and spatial population structure. Taxa that undergo dispersal and move more slowly are more likely to suffer from road mortality. The extent of the direct and indirect effects of roads has been revealed in numerous studies, with the greatest amount of data available for anurans and snakes. Excessive rates of mortality (thousands) have been documented for several species. Research indicates that the combined ecological effects may extend outward from the road edge beyond 100 meters, delineating a “road-effect zone.” Altered roadside habitats have been shown to modify amphibian and reptile behavior and movement patterns. Increased mortality and barriers to movement may influence species demography and gene flow, consequently having an impact on overall population stability and persistence. 2 Although relatively few studies address the population-level consequences of roads, population declines in several anuran, snake, and tortoise species have been shown to be associated with roads. Species with restricted distributions and/or small population sizes appear to be more vulnerable to extinction because of their sensitivity to stochastic changes. Species reliant on metapopulation structure are considered more vulnerable to habitat fragmentation because subpopulations periodically go extinct locally and must be re-established by dispersal from neighboring sources. Road-crossing structures and other methods (e.g., signs and road closures) have been used with varying degrees of success to address the negative impacts of roads on amphibians and reptiles. Types of road-crossing structures include amphibian and reptile tunnels, wildlife culverts, modified drainage culverts, wildlife underpasses, and wildlife overpasses. Several studies have shown that these passages can be very effective in decreasing levels of road mortality and isolation. The effectiveness of road-crossing structures is influenced by attributes such as structure type and dimensions, substrate and placement with respect to particular habitats. We provide recommendations for future work to understand and mitigate the effects of roads on amphibians and reptiles, including: (1) conducting research to determine if roads and vehicles inhibit movement of amphibians and reptiles; (2) investigating the diversity of impacts that roads and traffic have on amphibian and reptile populations (cf. road mortality) at broad spatial and temporal scales (> one generation); (3) acquiring and incorporating information on the location and importance of road-kill sites to improve placement of road-crossing structures; (4) identifying key habitat features that serve as corridors to movements through GIS spatial modeling; (5) conducting field experiments and monitoring studies that evaluate the efficacy of road-crossing structures and determine maintenance requirements; (6) establishment of performance standards for structures based on characteristics and needs of wildlife; and (7) developing ways to communicate this information effectively and efficiently to all interested parties and provide means for feedback as an ongoing, iterative process. Introduction The goal of this document is to review the effects of roads on amphibians and reptiles with an emphasis on the adverse biological and ecological effects and how to mitigate them. 3 Recently, concerns regarding observation of widespread amphibian and reptile population declines have been published (Alford and Richards 1999; Gibbons et al. 2000; Stuart et al. 2004). A document synthesizing what is currently known about road impacts is needed to facilitate investigations into the role that roads may play in contributing to those declines. Unlike many factors (such as global warming, increased ultra-violet radiation, and disease), the prospect of mitigating the adverse effects of roads seems more attainable. We believe that the better we understand this subject, the more effective we will be in minimizing the detrimental effects that our roads have on these animals. This document includes a bibliographic database of the effects of roads on amphibians and reptiles that may be searched by author, taxonomic group, geographic area, and subject (e.g., fragmentation, genetic effects, road-crossing structures) within the ISI ProCite and Adobe Acrobat programs. Our literature review is more restricted than the database and specifically addresses the following questions: (1) What is the scientific evidence for the need to provide mitigation for the detrimental effects of roads on individual amphibians and reptiles and on their populations? and (2) What types of methods have been used to address detrimental impacts and, if known, how effective have they been? We consider how types of roads, the surrounding environment, and different species and life stages may influence the effectiveness of mitigation. This report does not attempt to provide detailed specifications concerning the construction of road-crossing structures, as these suggestions will vary with each project. Finally, the report contains recommendations for future actions (experimental studies, meetings, publications, workshops, etc.) to better address the issue of the detrimental effects of roads on amphibians and reptiles. Methods To create a bibliography of the literature addressing the ecological effects of roads and traffic on amphibians and reptiles including mitigation efforts, we conducted literature searches at the University of Wisconsin (Madison; Stevens Point), University of Georgia, Savannah River Ecology Laboratory, and Idaho State University libraries. Articles summarizing original investigations, reviews, and conference proceedings were located, some through interlibrary loan. The majority of publications were found by searching journals and databases including 4 Agricola, Biological Abstracts, BioOne, Ecology Abstracts, Science Citation Index, and Wildlife Worldwide. Keywords used to search the databases included: alligator, amphibian, bridge, construction, culvert, density, effects, fragmentation, frog, habitat, highway, intensity, lizard, mitigation, movement, mortality, overpass, population, reptile, road, road-kill, salamander, snake, toad, tortoise, traffic, tunnel, turtle, underpass, and viaduct. In addition to the references in print, the survey revealed several literature databases that are in electronic form. 1. The Center for Transportation and the Environment (CTE) maintains several databases of environmental research including the Wildlife Ecology in Transportation bibliographic database of literature and web sites on wildlife issues in transportation. {www.itre.ncsu.edu/cte/wildlife.htm} 2. The U.S. Department of Transportation, National Transportation Library maintains the TRIS Online Database that contains 491,577 records of published transportation research (as of July, 2004). The International Transport Research Documentation database is also available for additional international material. {ntl.bts.gov/} 3. The U.S. Department of Transportation - Federal Highway Administration maintains a Critter Crossing website that serves as a database for current mitigation efforts to reduce wildlife mortality on roads. {www.fhwa.dot.gov/environment/wildlifecrossings/} 4. The Swedish National Road Administration Library Database contains 38,000 records of Swedish and foreign literature on the design, construction and maintenance of roads, bridges and tunnels, and on road traffic safety, the environment, transport and vehicle technology. {www.vv.se/biblio/english/} 5. Road-RIPorter Roads Bibliographic database was compiled by the Wildlands Center for Preventing Roads (CPR), and contains approximately 10,000 citations - including scientific literature on erosion, fragmentation, pollution, effects on wildlife, aquatic and hydrological effects, and other information on the impacts of roads. {www.wildlandscpr.org/databases/index.html} The references cited in this paper are included in a literature database maintained by the authors in ProCite format. This database is organized alphabetically by author’s last name as 5 well as categorically by subject and taxa and currently includes about 250 references. This document and the accompanying ProCite database are also available in Adobe Acrobat (PDF) format. Effects of Roads Organization To provide a framework for describing, relating, and summarizing the results from the diverse literature on the effects of roads on amphibians and reptiles, we developed the conceptual approach illustrated in Figure 1. The characteristics of the roads themselves (i.e., construction activities, road type, the overall road density in an area, and traffic level and patterns) are considered independent variables that potentially affect amphibians and reptiles, both directly and indirectly. Direct effects are considered to involve injury or mortality occurring during road construction (e.g., inadvertent burial or death from blasting) or subsequent physical contact with vehicles. Indirect effects include habitat loss, fragmentation, and alteration (e.g., changes in temperature, moisture, light, noise, pollutants, or quality of available habitat). Such changes may influence the behavior, survival, growth, and reproductive success of individual animals. For example, increases in the noise and light levels may disorient an animal, preventing them from crossing a road by posing a risk or obscuring cues necessary to follow certain paths, thus interfering with access to cover, food, and mates. The summed direct and indirect effects on individual animals may have population-level consequences (e.g., size, spatial structure, and persistence). Similarly, the summed effects on different species may influence the overall number of species in an area (i.e., species richness). These effects may be especially problematic when they affect sensitive, threatened, or endangered species or interfere with important ecosystem processes. 6 Figure 1. Conceptual framework for describing, relating, and summarizing results from the literature on the effects of roads on amphibians and reptiles. 7 Characteristics of Amphibians and Reptiles That Influence Susceptibility to Road Effects Amphibians and reptiles possess a variety of biological characteristics that influence their vulnerability to road effects. Factors influencing the frequency, speed, distance, and timing of movements can increase susceptibility to direct road mortality. Characteristics such as ectothermy (body heat derived primarily from external sources), skin permeability (esp. amphibians), and behavioral responses to light and noise can increase susceptibility to indirect effects. In addition, individual longevity, and population variability and spatial structure may influence population size and persistence. The habitat requirements of amphibians and reptiles vary seasonally; therefore the distribution of resources across the landscape relative to roads can influence mortality. These resources are associated with refuge, mates, and prey that tend to be concentrated in distinct habitats that are patchily distributed. For example, some snakes within northern temperate regions make a loop-like migration from a communal hibernaculum to summer foraging habitats across relatively long distances [up to 17.7 km for the red-sided garter snake (Thamnophis sirtalis parietalis), Gregory and Stewart 1975; up to 11 km for the western rattlesnake (Crotalus viridis), Duvall 1986]. Additionally, amphibians migrate in mass numbers between breeding ponds and terrestrial habitats (Holdgate 1989; Ashley and Robinson 1996; Semlitsch 2000). These taxa are therefore dependent on “landscape complementation” (a measure of proximity of critical habitat types and dispersal ability of the organism) to successfully complete their life cycles (Dunning et al. 1992; Pope et al. 2000). When roads fragment such habitats, the probability that individuals will be killed or injured by traffic during movements in search of resources, increases, as does the resistance of the landscape to such movements (Fahrig and Grez 1996). An individual’s vulnerability to road mortality is influenced by dispersal ability as well as the spatial scale and frequency of movements. Research indicates that more vagile (i.e., tending to change location over time) species are more likely to suffer from road mortality. In studying five amphibian species across a gradient of habitat loss, Gibbs (1998b) determined that species with low dispersal rates were more likely to persist in landscapes with low habitat cover, such as roadside areas, than vagile species. Carr and Fahrig (2001) suggest that as dispersal distances increase so does the likelihood of road encounter, and consequently mortality risk for a given anuran species. Furthermore, the population density of the more vagile northern leopard frog 8 was negatively impacted by traffic density within a 1.5 km radius of a pond; however, there was no evidence that traffic density impacted the population density of the less vagile green frog (Rana clamitans). Similarly, a study designed to examine the mortality patterns for snake populations in France provides evidence that species which move frequently over long-distances experience higher mortality than sedentary foragers (Bonnet et al. 1999). The researchers concluded that the movement patterns of snakes might be indicative of their susceptibility to direct mortality. Studies associate peaks of road mortality with higher movement frequencies due to season, sex, and life stage. For amphibians, road mortality may be proportionally high during pulses of movement related to fluctuations in water level (Smith and Dodd 2003), breeding (McClure 1951; Hodson 1966; Fahrig et al. 1995; Ashley and Robinson 1996), and dispersal (McClure 1951; Palis 1994; Ashley and Robinson 1996; Smith and Dodd 2003). Reptile examples comprise migratory behavior including movements related to fluctuations in water level (Bernardino and Dalrymple 1992; Aresco 2003; Smith and Dodd 2003; D. Jochimsen unpub. data), adult males searching for mates (Bonnet et al. 1999; Whitaker and Shine 2000; D. Jochimsen unpub. data), nesting migrations of adult females in the spring (Fowle 1996; Bonnet et al. 1999; Haxton 2000; Baldwin et al. 2004), and neonatal dispersal during late summer or early autumn (Bonnet et al. 1999; Enge and Wood 2002; Smith and Dodd 2003; D. Jochimsen unpub. data). Vulnerability to road mortality may also increase when movement pulses coincide with increased traffic volume. Dalrymple and Reichenbach (1984) noted a considerable rise in the road mortality of snakes, including the endangered plains garter snake (Thamnophis radix), when fall migrations to over-wintering burrows overlapped with intensified levels of sportsmen activity in a wildlife area in Ohio. Data collected on the directionality of massasauga rattlesnakes (Sistrurus catenatus) caught crossing Loop Road in Squaw Creek Wildlife Refuge, Missouri verified seasonal variation of habitat use within this population (Seigel 1986). Snake movements occurred during periods of increased human visitation to the refuge, and resulted in higher road mortality during both spring and autumn migrations. Additionally, Bernardino and Dalrymple (1992) found that the seasonal migration of snakes in Everglades National Park was significantly affected by the fluctuation of water levels. An increased movement of snakes during the dry season coincided with a greater influx of visitors to the park, resulting in 56% of 9