Individual study: Tunnels greater than 0.5m in diameter, lined with soil or gravel, with a 0.6–0.9 m high drift fence was considered most effective for four frog and turtle species tested in the USA
Woltz H.W., Gibbs J.P. & Ducey P.K. (2008) Road crossing structures for amphibians and reptiles: informing design through behavioral analysis. Biological Conservation, 141, 2745-2750
This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.
Install barrier fencing along roads
A replicated study in 2005–2006 of different height barrier fencing in a Wildlife Management Area, New York, USA (Woltz, Gibbs & Ducey 2008) found that fences of at least 0.6 m excluded most green frogs Rana clamitans and leopard frogs Rana pipiens. Fences 0.6 m high were more effective at excluding frogs (97–100%) than 0.3 m fences (77–80%). Only one leopard frog climbed over the 0.9 m high fence. Opaque, corrugated plastic fences were used to construct three nested, circular enclosures of heights 0.3, 0.6 and 0.9 m. Local green frogs (n = 135) and leopard frogs (n = 187) were placed in the centre of each arena and left for 15 min to attempt to scale the fences.
Install culverts or tunnels as road crossings
A replicated study in 2005–2006 of tunnels in a Wildlife Management Area in New York, USA (Woltz, Gibbs & Ducey 2008) found that green frogs Rana clamitans and leopard frogs Rana pipiens showed some preference for particular tunnel types. Green frogs showed a significant preference for soil (40%) and gravel (38%) linings, compared to concrete (13%) and PVC (9%). Leopard frogs showed no preference (19%, 32%, 29%, 19% respectively). Leopard frogs tended to prefer larger diameters (0.8 m: 35%; 0.6 m: 12%; 0.5 m: 28%; 0.3 m: 25%) and avoid the longest tunnels (9 m: 15%; 6 m: 40%; 3 m: 22–24%). Green frogs showed no preference for diameter (0.8 m: 33%; 0.6 m: 24%; 0.5 m: 27%; 0.3 m: 16%) or length (9 m: 32%; 6 m: 23%; 3 m: 19–26%). Tunnels with the greatest light permeability were preferred (4% light permeability: 39–41%; 1.3% light: 14–17%; 0.6% light: 24–26%; no light: 17–24%). Choice arenas had four different PVC culverts radiating out, which local green frogs (n = 135) and leopard frogs (187) could select to exit through. Frogs were tested in groups of 1–17 individuals, once per arena. Trials lasted 15 minutes, after 5 minutes acclimatization, in June–August 2005–2006. Pitfall traps captured animals at the end of each tunnel.