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Effective culvert placement and design to facilitate passage of amphibians across roads


—Efficient deployment of culverts to mitigate mortality of amphibians on roadways requires
identification of locations within road networks where animals cross (hotspots), points within identified
hotspots for culvert placement, and attributes of culverts that make them behaviorally palatable to migrating
individuals. In this study, we assessed road crossing frequency of Spotted Salamanders, Ambystoma
maculatum, and American Toads, Anaxyrus americanus, along a 700-m transect within a known crossing
hotspot, and related these distributions to habitat variables within the hotspot including the presence of
existing culverts. We also placed experimental arrays of culverts of varying attributes in the path of migrating
Spotted Salamanders to examine culvert preference by salamanders under typical movement environments
and appropriate animal behavioral states. Our studies of patterns of road occurrence demonstrated that both
species avoided crossing where there was a wetland within 15 m of the downslope of the road and that
neither species showed a strong preference for crossing near existing culverts. When considering the choice
for experimental culverts by Spotted Salamanders, we found no preference for culverts of varying aperture
size, length, or substrate. Our results indicate that patterns of occurrences of the two species of amphibian
within a crossing hotspot may be linked to the physical attributes at the site. For Spotted Salamanders in
particular, predicting where they will cross within a hotspot may not be easy. Spotted Salamanders showed
little preference for culverts of different design, indicating that a variety of culvert designs can suffice for
mitigation if placed in appropriate locations.