Action: Close roads during seasonal amphibian migration
- Two studies (including one replicated study) in Germany found that large numbers of amphibians were protected from death during breeding migrations at road closure sites and at road closure sites with assisted crossings and barrier fences.
Road traffic can have significant effects on amphibian populations, particularly where their annual migration routes between overwintering and breeding sites cross roads. In some areas, roads can be closed to protect important migration routes.
One study showed that reducing traffic on minor roads by creating a highway prevented fragmentation of populations of palmate newts Lissotriton helveticus but not midwife toads Alytes obstetricans (Garcia-Gonzaleza et al. 2012).
Garcia-Gonzaleza C., Campoa D., Polaa I.G. & Garcia-Vazqueza E. (2012) Rural road networks as barriers to gene flow for amphibians: Species-dependent mitigation by traffic calming. Landscape and Urban Planning, 104, 171–180.
Supporting evidence from individual studies
A before-and-after study in 1983 of a road in Oberbergischer Kreis, Germany (Karthaus 1985) found that closing the road allowed common toads Bufo bufo to successfully cross. While the road was open none of the young amphibians reached the other side. However, one hour after closure about 100,000 toads were found crossing along a 400 m section of the road. The road was closed for eight days until the migration of amphibians was over in spring.
A replicated study in 1986 of 114 sites including at least 11 road closure sites, 60 amphibian barrier fences and 23 hand-collected human-assisted crossings in Nordrhein-Westphalia, Germany (Feldmann & Geiger 1989) found that 131,061 amphibians were protected from death on roads during breeding migrations. Between one and 116,515 individuals of 14 species were recorded at the road closure sites, assisted crossings and barrier fences at the 114 sites. Nine sites had a combination of two of the interventions and for 20 sites it was unknown which of the interventions were used.
- Karthaus G. (1985) Schutzmaßnahmen für wandernde amphibien vor einer gefährdung durch den Staßenverkehr - beobachtungen und erfahrungen. Natur und Landschaft, 60, 242-247
- Feldmann R. & Geiger A. (1989) Protection for amphibians on roads in Nordrhein-Westphalia. Amphibians and Roads: Proceedings of the Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 51-57.