Keeping salamanders off the streets: An assessment of one of the first amphibian road tunnels in the United States 30 years after installation

Abstract

Culverts are often installed under busy roads to help animals ranging from small frogs to bears safely cross roads that bisect their habitat. One of the first roadway culvert systems designed specifically for amphibian use in the United States was installed along Henry Street in Amherst, Massachusetts in 1987. The purpose of these under-roadway tunnels was to protect spotted salamanders (Ambystoma maculatum) during their annual migration from their hibernation area to their breeding pools, which are separated by a road. Anecdotal evidence from volunteers monitoring the site suggested that salamanders were no longer using the tunnels. To evaluate this concern, we conducted salamander counts to quantify the amount of tunnel use. In 2016, only 11% of the observed salamanders used the tunnels. Subsequently, we implemented two tunnel modifications in an effort to increase salamander tunnel usage above the baseline established in 2016. Unfortunately, neither retrofit was successful in increasing use. Previous studies have demonstrated that salamanders prefer minimum tunnel apertures of >0.4 meters, so it is likely that the 0.2 meter tunnel apertures used here are too small. This may create a differential in light and humidity between the environments inside and outside the tunnels that is recognized by the salamanders. While many studies have evaluated amphibian tunnel use in lab and field settings, ours is one of the first studies to have examined tunnel usage data long after initial tunnel installation. These long-term data are critical for evaluating what factors are necessary for maintaining tunnels over decade-long time scales.