Road mitigation using tunnels and fences promotes site connectivity and population expansion for a protected amphibian

Laurence E Jarvis,Silviu O Petrovan,Michael Hartup

doi:10.1007/s10344-019-1263-9

Laurence E Jarvis, Silviu O Petrovan + Show 1 more

Open Access

https://doi.org/10.1007/s10344-019-1263-9

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Abstract

Habitat loss and fragmentation due to urbanisation and road developments have substantial impacts on amphibian populations and road mitigation measures are increasingly used in order to reduce such risks. However, numerous important questions remain unanswered on the actual effectiveness of such ecological road mitigation projects. We used specially adapted time-lapse recording cameras and a custom image analysis script to monitor the amphibian usage and effectiveness of a multi-tunnel mitigation site in northern England over 4 years and used before-and-after pond survey data to evaluate the mitigation results from a population trend perspective. We monitored four amphibian species, including the European protected great crested newt (Triturus cristatus), the main target of amphibian road mitigation in the UK. Despite substantial evidence of mitigation rejection and U-turn movements inside the tunnels, overall, most amphibians entering tunnels successfully used them to move between the different parts of the site separated by the road. Road fences appeared effective for preventing amphibian road mortality and site connectivity was re-established via the wildlife passage system, with multiple new ponds across the road colonised by amphibians. Unlike frogs and toads, tunnel usage by newts was strongly autumn based, indicating that such systems are mainly suitable for supporting newt dispersal movements between breeding areas. The great crested newt population increased rapidly over the course of the monitoring period, suggesting that, together with habitat replacements and improvements, the road mitigation measures were effective at maintaining site connectivity and as a population conservation measure.

Highlights

The unprecedented expansion of transport infrastructure over the past decades has had major impacts on amphibian populations worldwide (Fahrig et al 1995; Glista et al 2008; Beebee 2013), causing habitat loss, pollution and fragmentation as well as substantial rates of road traffic mortality (Hels and Buchwald 2001; Mazerolle 2004; Petrovan and Schmidt 2016)
243 adult great crested newts, 322 juvenile great crested newts, 67 adult smooth newts, 161 juvenile smooth newts, 69 adult common frogs and 189 common toads were observed in the tunnels (Table 1) (Fig. 2)
The monitoring of the tunnels and ponds indicates that this mitigation system provided a successful measure to prevent road mortality and a well-used movement corridor between aquatic habitats for great crested newts and other amphibian species

Summary

Introduction

The unprecedented expansion of transport infrastructure over the past decades has had major impacts on amphibian populations worldwide (Fahrig et al 1995; Glista et al 2008; Beebee 2013), causing habitat loss, pollution and fragmentation as well as substantial rates of road traffic mortality (Hels and Buchwald 2001; Mazerolle 2004; Petrovan and Schmidt 2016). Tunnel usage by amphibians appears highly variable both within and between species and pitfall trapping can introduce bias in the data by restricting animal movement. It typically requires licenced personnel and is inherently expensive given that traps need to be checked at least twice daily. It typically requires licenced personnel and is inherently expensive given that traps need to be checked at least twice daily. Pagnucco et al (2012) found that the crossing success rate in the long-toed salamander (Ambystoma macrodactylum) in North America was 23% in immigrating individuals but only 1% in emigrating individuals, highlighting large seasonal differences within the same population

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