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Maintain habitat connectivity: Amphibian and reptile tunnels
Priority areas for terrestrial connectivity for wetland? and aquatic ecosystems are represented as green dots on roads. If these are not visible, use the plus sign to zoom in. You can layer in results as top 5%, top 10%, top 15% and top 20%; darker colors represent higher priorities. Data are from the Critical Linkages Phase I (2011).Hide
Priority areas for terrestrial connectivity for wetlandRead More
Adaptation Strategies and Actions
Maintain habitat connectivity: Amphibian and reptile tunnels
Restore and maintain terrestrial and aquatic connectivity sufficient to maintain healthy ecosystems and wildlife populations
Animal movements (individuals or their offspring) across the landscape are important for maintaining healthy wildlife populations. Climate change is likely to result in changes to habitat conditions (temperature, rainfall, vegetation) that will require adjustments in the areas occupied by many species. Restoring and maintaining landscape connectivity sufficient to allow wildlife populations to adjust their distribution over time is a critically important strategy for adapting to climate change.
Construct and monitor crossing structures for amphibians and reptiles at strategic locations
In 1987, the first amphibian tunnels in North America were constructed in Amherst, Massachusetts. The “Henry Street Tunnels” as they came to be known were an experiment in conservation to see if wildlife crossing structures could be used to reduce mortality and restore connectivity for amphibians. Since then, a number of amphibian and reptile tunnels have been constructed in Massachusetts and across North America (they had been used throughout Europe prior to the Henry Street experiment).
Lessons learned from amphibian and reptile structures that have been constructed and monitored, and a limited number of control experiments, suggest that amphibian and reptile tunnels can be an important tool for restoring terrestrial connectivity, but they must be used strategically (only at certain locations) and carefully designed and constructed.
To be effective, amphibian and reptile tunnels need to be located where animals are likely to cross roads. Tunnels can be a particularly effective conservation tool if also located in areas identified by landscape modeling to be important for maintaining terrestrial connectivity among wetland? and aquatic ecosystems (see maps on this page). Crossing structures should be large enough to accommodate all species likely to cross (e.g. adult snapping turtles) and designed with open tops (slotted or grated) to allow adequate moisture (rain) and light throughout the tunnel.
Amphibians require moist conditions; wetness during rainy weather is often a migratory cue for frogs and salamanders. Crossing structures that are dry on the inside are not likely to be as effective as open top structures. A recent study at the University of Massachusetts Amherst found that light is an important determinant of crossing structure effectiveness for turtles. Small structures (2’x2’) with lighting that simulated an open top out performed much larger structures with closed tops.
Unless amphibian and reptile crossing structures are located in areas that naturally funnel animals to a particular point on the road, guide fencing or walls will be required. Guide fencing can be made out of wood, filter fabric (“silt fencing”), aluminum flashing, or wire or plastic mesh. Guide walls are generally constructed to provide a barrier in only one direction. They present a barrier to animals approaching a road and guides them toward the crossing structures. However, these walls are flush with the ground surface on the road side of the barrier so that animals that make it onto the road surface can drop down over a mini retaining wall and move away from the road.
Particular design features may be necessary to facilitate tunnel use by certain species. Size, placement, moisture, hydrology, temperature, and noise have all been demonstrated to affect wildlife use of underpasses. Until a tunnel design is tested for a wide variety of species, they are not recommended for wide application. If a tunnel does not meet the needs of a wide variety of species, fences, necessary to channel some wildlife to the tunnels, may actually function as barriers to movement for other species.
Therefore, tunnels are only recommended when:
1. There is a documented need.
- Is there a known population at risk?
- Is there a known crossing point?
- Are rare species involved?
- Will traffic volumes be high enough to represent a serious threat?
- Are we dealing with a species that is vulnerable to road mortality (e.g. species characterized by low reproductive potential and high adult survival rates like turtles and mole salamanders)?
2. The benefits for a particular species outweigh the risks to other species that may have their movements blocked if the tunnels don't function as intended.
3. The tunnel system is carefully designed, located and constructed.
4. An adequate maintenance plan is in place.
Until tunnels have been tested and shown effective for a range of small wildlife, use of tunnels is not recommended for most sub-division or light volume access roads.
For smaller roads and driveways, the most important design feature to consider is curbing. Granite curbs and some traditional curbing can act as a barrier to amphibian and hatchling turtle movements. In Massachusetts and Canada, large numbers of salamanders have been intercepted in their migrations by curbs and catch basins. Use of Cape Cod berms rather than traditional curbing may be one solution. Alternatively, where storm water management systems require more traditional curbing, it may be possible to design in escape ramps on either side of each catch basin.
Target Species, Species Groups, Habitats and Stressors
Scope and Constraints
1. Andrews, K..M., P. Najappa, and S.P.D. Riley (Eds). 2015. Roads and Ecological Infrastructure: Concepts and Applications for Small Animals. Johns Hopkins University Press. Baltimore MD. 304 pp.
2. Jackson, S. D. 1996. "Underpass Systems For Amphibians" Trends in Addressing Transportation Related Wildlife Mortality. Ed. G.L. Evink, P. Garrett, D. Zeigler and J. Berry. Tallahassee, FL: State of Florida Department of Transportation, 1996.
3. Jackson, S. D. and T. F. Tyning. 1989. "Effectiveness of drift fences and tunnels for moving spotted salamanders Ambystoma maculatum under roads" Amphibians and Roads. Ed. Thomas E. S. Langton. Shefford, England: ACO Polymer Products, 1989. 93-99.
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