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Providing evidence to improve practice

Action: Install tunnels/culverts/underpass under railways Terrestrial Mammal Conservation

Key messages

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  • Survival (1 study): A review found that most studies recorded no evidence of predation in or around passages under railways or roads of mammals using those passages.


  • Use (5 studies): Five studies, in Spain, Australia, Canada and the Netherlands, found that tunnels, culverts and underpasses beneath railways were used by a range of mammals including rodents, rabbits and hares, carnivores, marsupials, deer and bears. One of these studies found that existing culverts were used more than were specifically designed wildlife tunnels.

Supporting evidence from individual studies


A site comparison study in 1984–1985 in New South Wales, Australia (Hunt et al. 1987) found that small and medium-sized mammals used established drainage culverts, but rarely used new wildlife tunnels. All five existing culverts were used by mammals. Bush rat Rattus fuscipes was recorded in all culverts (1–6 captures and/or tracks/culvert) and long-nosed bandicoot Perameles nasuta in one. Few signs of use were recorded in wildlife tunnels. Swamp wallaby Wallabia bicolor tracks were recorded in one tunnel in October 1984. No indication of tunnel use was found in January 1985. Five long-established drainage culverts (0.2 × 0.9 to 2.4 × 3.0 m) with dense surrounding vegetation and three of seven newly constructed wildlife tunnels (3 m diameter, 15–20 m long) with sandy floors and little vegetation, under a 35-km-long section of railway line, were monitored. Small mammal traps were set in all underpasses and cage traps in tunnels and one culvert. Tracks were recorded in sand and on soot-coated paper across passages. Culverts were surveyed for eight nights in September–October 1984 and tunnels for seven nights in October 1984 and five nights in January 1985 (15–242 trap nights/structure).


A replicated study in 1994 of 17 culverts under roads and railways in Madrid province, Spain (Yanes et al. 1995) found that mammals used all 17 culverts studied. The highest frequencies of tracks was from wood mice Apodemus sylvaticus (2.5 tracks/culvert/day), shrews Sorex spp. (0.5/culvert/day) and European rabbit Oryctolagus cuniculus (0.3/culvert/day). Rats Rattus sp. (0.1 tracks/culvert/day), hedgehogs Erinaceus europaeus (0.01/culvert/day), cats (mostly wild cat Felis sylvestris - 0.04/culvert/day), red fox Vulpes vulpes (0.03/culvert/day), genet Genetta genetta (0.02/culvert/day) and weasel Mustela nivalis (0.01/culvert/day) were also detected. Small mammal use of culverts decreased with increased culvert length and increased with increasing culvert height, width and openness. Use by rabbits and carnivores decreased with increasing width of the railway or highway. Rabbit use also declined with increased boundary fence height. Vegetation complexity had little influence. Five culverts were monitored under railways, two under a motorway and 10 under local roads. Structural, vegetation and traffic variables were recorded at each culvert. Use was monitored using marble (rock) dust over culvert floors to record tracks. Sampling was undertaken in 1994, over four days each in spring, summer, autumn and winter. Sampling of four culverts extended to eight days when deer were in the vicinity.


A study in 1991–1992 along a high-speed railway through agricultural land in Castilla La Mancha, Spain (Rodriguez et al. 1996) found that culverts and underpasses not specifically designed for wildlife were used as crossings under the railway by a range of mammals. Small mammals were recorded in culverts/underpasses (and two overpasses) 582 times (37 crossings/100 passage-days) and brown hare Lepus granatensis and European rabbit Oryctolagus cuniculus 89 times (5 crossings/100 passage-days). Tracks of four carnivore species, red fox Vulpes vulpes, wild cat Felis silvestris, common genet Genetta genetta and Iberian lynx Lynx pardinus, were recorded. No deer or wild boar Sus scrofa used passages. Rabbit and hare crossing rates were not affected by underpass design, vegetation cover at entrances or distance from scrubland. Small mammals preferred culverts ≤2 m wide. Fencing did not significantly affect relative crossing rates. Fifteen dry culverts and passages (e.g. small roads and two flyovers, 13–64 m long, 1.2–6.0 m wide, 1.2–3.5 m high) along a 25-km section of high-speed railway, were monitored. Tracks in sand were monitored at each passage for 15–22 days/month between September 1991 and July 1992. The railway was fenced with 2-m-high wire netting in July 1991–March 1992.


A review in 2000 of studies investigating whether mammalian predators use wildlife passages under railways and roads as ‘prey-traps’ (Little et al. 2002) found that most studies recorded no evidence of predation in or around passages. Evidence suggested that predator species used different passages to their prey. Only one study, in Australia, suggested that tunnels increased predation risk and that recorded only one predator in tunnels. However, no studies specifically investigated predator activity, densities or predation rates, or predator-induced prey mortality at passage sites relative to control sites away from passages, or before-and-after passage construction. A literature survey was carried out in July 2000 using BIOSIS (Biological Abstracts) and Proceedings of the First, Second and Third International Conference on Wildlife Ecology and Transportation.


A study in 2003 of culverts under a railway and highway in British Columbia, Canada (Krawchuk et al. 2005) found that at least two of three underpasses were used by mammals. Mule deer Odocoileus hemionus were detected using one small culvert (2.1 m wide, 1.5 m high, 30 m long) six times. They were not recorded using a larger (7 m wide, 5 m high, 40 m long) cattle underpass though signs of their presence were noted nearby. Black bears were detected 20 times passing through the smaller culvert and four times through the cattle underpass. Raccoons were detected twice at the cattle underpass. The smaller culvert had a soil substrate, was surrounded by vegetation and was relatively far from human activity. The cattle underpass had limited surrounding natural vegetation. No mammals were recorded using a third culvert (1.2 m wide and high, 30 m long), possibly due to camera malfunction. Culverts and the underpass ran under both the Canadian Pacific Railway and Trans-Canada Highway. They were monitored using infrared sensor cameras during August–November 2003. Animal tracks or signs around camera stations were also recorded.


A study in 2003 at 14 underpasses beneath a railway through suburban and rural habitat in the Netherlands (van Vuurde & van der Grift 2005) found that several species of small- and medium-sized mammals used underpasses to cross the railway. Tracks identified in the monitored underpasses were from western hedgehog Erinaceus europaeus (recorded at two of the 14 underpasses), rabbit Oryctolagus cuniculus (two underpasses), brown rat Rattus norvegicus (4–5 underpasses), western polecat Mustela putorius (0–1 underpasses), red fox Vulpes vulpes (one underpass), mice, voles and shrews (13 underpasses), weasel Mustela nivalis and stoat Mustela erminea (11 underpasses) and pine Martes martes and stone marten Martes foina (one underpass). Ranges in the number of underpasses used reflect uncertainties in track identification. Fourteen underpasses (0.6 m wide, 0.3 m high and 19–32 m long), were installed beneath a 12-km stretch of railway in 1998–2003. Eleven underpasses were topped with grates (2–9 m long) between entrances and railway tracks. Mammal use was monitored between August and October 2003, using ink track-plates (0.6 × 2.4 m). Track-plates were checked on average at eight-day intervals.

Referenced papers

Please cite as:

Littlewood, N.A., Rocha, R., Smith, R.K., Martin, P.A., Lockhart, S.L., Schoonover, R.F., Wilman, E., Bladon, A.J., Sainsbury, K.A., Pimm S. and Sutherland, W.J. (2020) Terrestrial Mammal Conservation: Global Evidence for the Effects of Interventions for terrestrial mammals excluding bats and primates. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.