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
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.
Three wildlife overpasses were constructed in 2006 on the new route 18 north of Herning in Denmark. Mammals’ use of these overpasses was recorded during 5 day periods in the autumn months of 2010. Medium and large sized mammal species were detected with track beds. Small mammal species were recorded with live traps. Small mammals were marked to record recaptures and movements. Bat activity was recorded at two of the overpasses using automatic ultrasound detectors, live monitoring with ultrasound detectors and direct observations for three nights in late August. Real-time, full-spectrum ultrasound recording or recordings of the time-expanded calls were used to identify bat species from their echolocation calls.
The mammals’ use of the three wildlife overpasses was compared with the use of two older overpasses in Denmark (at Jyske Ås and Lillering) from an earlier study (Christensen et al. 2007). The data from this earlier study were used to evaluate the efficiency of a three-month monitoring period compared to a 12 month monitoring period. Finally we assess the wildlife overpasses and suggest recommendations for the dimensions for future wildlife overpasses in Denmark.
Roe deer and red fox were recorded most regularly on all the three wildlife overpasses near Herning. The lowest activity of roe deer was recorded on an overpass located in an arable area. Brown hare, badger and medium-sized mustelids 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.
Two of the three new wildlife overpasses near Herning are located near forests and a large meadow. The third overpass is located in an agricultural area with no ecological corridors to forest or nature areas. Human disturbance on the overpasses is probably insignificant, and there are no other large infrastructures or buildings in a 200 m buffer zone around all the three overpasses. The diversity and structure of the vegetation on the ramps leading up to the overpasses and across the passages is very homogeneous. To increase probability that a wider range of species will use the overpasses the diversity and structure of the vegetation and microhabitats on the surface should be increased to create more diverse habitats and corridors for e.g. small mammals, reptiles, amphibians and terrestrial invertebrates.
There were no significant differences between the monthly use of the three new overpasses near Herning and the two older overpasses at Lillering and Jyske Ås by large and medium-sized mammals, roe deer and red fox. However, small mammals were recorded significantly more often on the overpass at Jyske Ås. This is probably caused by a more dense and diverse vegetation and more suitable habitats for small mammals on this overpass.
Animals’ use of fauna passages should be surveyed regularly to monitor whether the passages meet the needs for the species they were designed for. The most efficient three month period was during autumn, when the activity level of medium and large mammal species on the passages and the population sizes of small mammal species are highest. More than 60 % of the medium and large mammal species recorded during a 12 month monitoring period would had been detected if the survey period was restricted to the three month during autumn. Only 49 % of the small mammal species was detected during a three month monitoring period in the autumn. However, on the wildlife overpasses 91 % of the small mammals were detected. The underpasses were not designed as passages for the small mammal species and the total number of small species detected in the underpasses was very low.
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:
