Effectiveness of wire netting fences to prevent animal access to road infrastructures: an experimental study on small mammals and amphibians

Transport infrastructures, such as highways, disrupt animal migrations and cause roadkill. To mitigate the latter problem, fences have been built but their effectiveness has rarely been tested under controlled conditions. Here, we tested the effectiveness of the most commonly used fence in France and probably in Europe (wire netting fence) to block animals. We tested the wire netting fence, with and without a structural modification (i.e. an overhang), with three small mammalian species (the European hamster: Cricetus cricetus Linnaeus, 1758; the common vole: Microtus arvalis Pallas, 1778 & the wood mouse: Apodemus sylvaticus Linnaeus, 1758) and two amphibian species (the marsh frog: Pelophylax ridibundus Pallas, 1771 & the European green toad: Bufotes viridis Laurenti, 1768). During testing, all small vertebrate species tested were placed into an arena, from which they could only escape by crossing the wire netting fence. Without an overhang, almost all adult individuals of all tested species were able to climb over a 30 to 40 cm high wire netting fence. Furthermore, the addition of an 8 cm long overhang at the top of the fence stopped the amphibian species tested but not the most agile mammalian species, such as the hamster and the wood mouse. Based on these results, we do not support the construction of wire netting fences along roads as a measure to stop small animals from crossing. We recommend the use of more effective and durable fences, which, in addition, can be associated with wildlife passages to reconnect isolated populations.