Large infrastructures like roads have direct and indirect impact on wildlife. Roads may restrict the animals’ dispersal and habitat use. To reduce the fragmentation of the landscape, fauna passages are constructed to allow the wildlife and other fauna a safe dispersal route across the road barrier. Experimental studies of the efficiency of large fauna passages have not been performed. Monitoring of the animals’ use of fauna passages are needed to optimise the design of new fauna passages.

Monitoring of the use of the three wildlife overpasses at Herning by mammals showed that roe deer and red fox crossed the overpasses most regularly. Brown hare, badger and medium-sized mustelids only crossed the overpasses occasionally. Among the small mammal species yellow-necked mouse, harvest mouse and common shrew were recorded most often. Pygmy shrew, bank vole, field vole, common vole, wood mouse were recorded in low numbers. Some of the yellow-necked mice and a bank vole crossed the overpasses during the study. Daubenton’s bat, serotine, Nathusius' pipistrelle, noctule and parti-coloured bat were detected, but the activity of bats was generally low in the area. It was not possible to conclude whether the bats cross the road along the overpasses.

The three wildlife overpasses near Herning and older Danish wildlife overpasses are all too narrow to function as efficient fauna passages for a broad range of species. Furthermore, to mitigate the barrier effect of roads for mammals efficiently the distance between suitable fauna passages must be smaller than presently practiced in Denmark. Based on the results from the Danish and other European studies NERI recommends the following guidelines for new wildlife overpasses in Denmark:

• Wildlife overpasses designed to meet the need for several species should have a minimum width of 50 m.
• Smaller overpasses designed to meet the specific needs of single smaller species should have a minimum width of 20 m.
• Wildlife overpasses for more species with different habitat use, e.g. mammals, reptiles, and amphibians, should have a minimum width of 80 m.
• The openness index should be minimum 0.8. Preferably it should be larger than 1.0.
• Combined use of overpasses as fauna and human passages is not recommended.

Contact: Scientist Morten Elmeros, tel. +45 8920 1727, elm@dmu.dk

Elmeros, M., Viñas, M.M., Andersen, P.N. & Baagøe, H.J. 2011. Undersøgelser af pattedyrs brug af faunabroer på rute 18 ved Herning. En biologisk vurdering med anbefalinger til forbedringer og fremtidig praksis for faunabroer. Danmarks Miljøundersøgelser, Aarhus Universitet. 48 s. – Faglig rapport fra DMU nr. 839. http://www.dmu.dk/Pub/FR839.pdf