Keeping salamanders off the streets: evaluating and modifying one of the first US amphibian road tunnels 30 years after installation

Abstract

Abstract Wildlife tunnels are often installed under busy roads to help a variety of animals, from small frogs to bears, safely cross roads that bisect their habitats. One of the first roadway wildlife tunnel systems designed specifically for amphibian use in the USA was installed along Henry Street in Amherst, Massachusetts, in 1987 to protect spotted salamanders (Ambystoma maculatum). These salamanders cross Henry Street during their annual migration to their breeding pools. In recent years, volunteers monitoring the site suggested that salamanders were no longer using the tunnels. To evaluate this concern, we conducted salamander counts in 2016, 2017 and 2018 to quantify tunnel use. In 2016, 11% of observed salamanders used the tunnels—a substantial decrease from 68% in 1988, 1 year after tunnel installation, when the tunnels were last evaluated. Following 2016, we implemented two tunnel modifications: adding a light to the far end of tunnels (2017) and placing a ramp at tunnel entrances to reduce balking (2018). However, salamander tunnel use was not increased significantly by either the light modification or the ramp modification. Previous studies have demonstrated that salamanders prefer minimum tunnel apertures of >0.4 m, so it is likely that the 0.2 m apertures at Henry Street are too small. While many studies have evaluated amphibian tunnel use in laboratory and field settings, ours was one of the first studies to examine tunnel usage data long after initial installation. These long-term data are critical for evaluating factors necessary for maintaining wildlife tunnel effectiveness over decades.