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

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.

A Combination of Environmental and Landscape Variables Drive Movement and Habitat use in TwoAnaxyrussp. in the Eastern Coastal Plain

“…The activity of toads on paths also suggests that managers should take care to warn any nocturnal visitors to their grounds that they should watch their step. While “Big Night” amphibian migration events do not generally occur in this region, our research and personal observations indicates that paths within protected areas are a major attractant of toads throughout their active period of the year (Hedrick et al, 2019). Our findings also have broader implications in the context of climate change, as the importance of environmental variables indicates the importance of climate and the weather it produces on amphibian behavior.…”

Do wildlife crossing structures mitigate the barrier effect of roads on animal movement? A global assessment

“…Hedrick et al. (2019) concluded that modifications to underpasses for salamanders were ineffective, despite an increase in crossings, as they served only a small percentage of the wider population. Thus, limited net loss targets must be underpinned by clear evidence that population persistence is maintained despite reduced levels of movement.…”

“…In other cases, the amount of movement may be considered insufficient, even if it is an improvement over unmitigated conditions. Hedrick et al (2019) concluded that modifications to underpasses for salamanders were ineffective, despite an increase in crossings, as they served only a small percentage of the wider population.…”

Elevated road segment (ERS) passage design may provide enhanced connectivity for amphibians, reptiles, and small mammals

“…Overall, permeability of passages to small animal movements appear to vary greatly according to species behavior, location, passage spacing, and passage characteristics (e.g., Lesbarrères et al, 2004;Pagnucco et al, 2012;Beebee, 2013;Langton and Clevenger, 2017;Hedrick et al, 2019;Jarvis et al, 2019;Matos et al, 2019;Schmidt et al, 2020;Boyle et al, 2021). Recent evidence and literature reviews are starting to indicate that wider passages are generally more permeable to more small animal species than small tunnels (e.g., Martinig and Bélanger-Smith, 2016;Langton and Clevenger, 2017;Schmidt et al, 2020), although small tunnels have been shown to be effective for species in some locations, particularly where spacing between passages was short (i.e., Helldin and Petrovan, 2019;Jarvis et al, 2019).…”