Temporal trends in use of fauna-friendly underpasses and overpasses

Published source details Bond A.R. & Jones N.J. (2008) Temporal trends in use of fauna-friendly underpasses and overpasses. Wildlife Research, 35, 103–112.
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This study is summarised as evidence for the following.

	Action	Category
	Install barriers and crossing structures along roads/railways Action Link
	Install tunnels/culverts/underpasses under roads/railways Action Link
	Install overpasses over roads/railways Action Link
	Install barrier fencing and underpasses along roads Action Link

Install barriers and crossing structures along roads/railways

A before-and-after study in 2004–2007 in dry eucalypt woodland in Queensland, Australia (Bond & Jones 2008) found that after an exclusion fence and vegetated overpass (‘land-bridge’) were built, one snake was found dead on the road compared to two before. Before construction of the fencing and overpass, one brown tree snake Boiga irregularis and one eastern small-eyed snake Cryptophis nigrescens were found as road-kill in the area and after the underpasses were constructed one carpet python Morelia spilota was found. In 2004 an exclusion fence, made of rubberised metal mesh (2.5 m high, 5 cm underground) with a rubber sheet (0.5 m high) running around the base, was built along a road overpass (see original paper for details) to a forest boundary on both sides of the bridge. Road-killed animals were surveyed by vehicle in the early mornings twice weekly before construction started in April–July 2004 and weekly after construction was completed in February 2005 until June 2007. All species larger than a blue-tongued skink Tiliqua scincoides were recorded.

(Summarised by: Katie Sainsbury)
Install tunnels/culverts/underpasses under roads/railways

A replicated, before-and-after study in 2004–2007 in dry eucalypt woodland in Queensland, Australia (Bond & Jones 2008) found that two road underpasses were used by reptiles from six months after construction was finished. Results were not statistically tested. Six to 12 months after construction of two underpasses, 0.6–1.3 lizards/day and 18–30 months after construction, 0.1–1.0 lizards/day were recorded using the underpasses. The authors reported that most of the reptiles recorded were medium-sized lizards. After construction, one snake Morelia spilota was found dead on the road, compared to two snakes (one Boiga irregularis and Cryptophis nigrescens) beforehand. In 2004, two underpasses were constructed (2.4 m high, 2.5 m wide, 48 m long) containing: a lower level (0.9 m wide), a raised level with rocks (1.6 m wide, 0.4 m above ground), a half log railing, and a wooden shelf (0.25 m wide, 1.2 m above ground) running the length of the underpass. Sand strips (1–2 cm deep, 1 m long, 2.5 m wide) were placed 1–2 m inside the underpasses at both ends and on the shelves (0.5 cm deep, 0.5 m long, 0.25 m wide). Sand was checked for tracks twice weekly in August 2005–February 2006 and monthly in June 2006–June 2007. Animals killed on the road were surveyed by vehicle in the early mornings twice weekly before construction started in April–July 2004 and weekly after construction was completed in February 2005–June 2007. All species larger than a blue-tongued skink Tiliqua scincoides were recorded.

(Summarised by: Katie Sainsbury)
Install overpasses over roads/railways

A study in 2004–2007 in eucalypt woodland in Queensland, Australia (Bond & Jones 2008) found that a wildlife bridge was used by mammals. A total of 1,240 herbivore scats were recorded on the bridge. Brown hare Lepus capensis scats were the most common (78%), followed by red-necked wallaby Macropus rufogriseus (15%), eastern grey kangaroo Macropus giganteus (5%), swamp wallaby Wallabia bicolor (1%), possum (1%) and short-beaked echidna Tachyglossus aculeatus (1%). Six mammals were killed on the road before construction and one afterwards. In 2004, a 1.3-km section of highway was upgraded to four lanes and a variety of wildlife crossings constructed, with barrier fencing (2.5 m high) between. Use of a large overpass (15–20 m wide, 70 m long, planted with grass, shrubs and trees) was monitored from six months after completion. Scats were recorded weekly from August 2005–February 2006 and for two weeks in June 2007. Road-kill was monitored twice weekly before construction (April–July 2004) and weekly afterwards, until June 2007.

(Summarised by: Rebecca K. Smith)
Install barrier fencing and underpasses along roads

A before-and-after study in 2004–2007 along a highway through eucalypt woodland in Queensland, Australia (Bond & Jones 2008) found that two underpasses, in areas with roadside barrier fencing, were used by mammals and the mammal road casualty rate fell after construction. There were three wild mammal road casualties over 29 months post-construction and six during four months pre-construction. This comparison was not tested for statistical significance. Tracks detected in underpasses were from rodents (370 tracks), house mice Mus musculus (115), Dasyurid sp. (most likely Common dunnart Sminthopsis murina) (17), northern brown bandicoots Isoodon macrourus (179), possums (16), red-necked wallabies Macropus rufogriseus (3), short-beaked echidnas Tachyglossus aculeatus (2) and from feral cats Felis catus, dogs Canis lupus familiaris and brown hares Lepus europaeus. Proportions of tracks representing full crossings varied by species with the highest figure for wild mammals being for possums (18–40% of records). In 2004, a 1.3-km section of highway was upgraded to four lanes and a variety of wildlife crossings constructed, linked by barrier fencing (2.5 m high). Use of two underpasses (2.4 m high, 2.5 m wide, 48 m long) with water flowing through and ledges attached to side walls, was monitored, starting six months after construction. Tracks were counted on sand within each entrance, twice weekly from August 2005–February 2006 and monthly from June 2006–June 2007. Road-kill was monitored twice weekly before (April–July 2004) and weekly after construction until June 2007.

(Summarised by: Rebecca K. Smith)