Use of wildlife passages by invertebrate and vertebrate species

Presented are the results of two studies (1993-97 and 2003-06) considering the use of different kinds of wildlife and non-wildlife over- and underpasses (green bridges, viaducts, culverts, etc.) by invertebrates and mammals. The passages varied considerably in width (1200 meters) and age (3-16 years). Animal groups studied were ground beetles, grasshoppers, butterflies, burnet moths, spiders, voles, shrews, dormice, bats, medium sized mammals (European hare, predators) and ungulates. Methods applied depend on the species investigated: trapping, mark and recapture, bat detectors, direct and infrared camera observations, track counts, telemetry etc. With a few exceptions, all species investigated used at least the wider over- and underpasses. This applies especially for the medium sized and large mammals which showed a strong preference for green bridges and viaducts. The larger box-shaped wildlife underpasses and those for small mammals unexpectedly were used only moderately. On the other hand even insects able to fly, like butterflies and burnet moths, and birds showed a preference for overpasses when crossing a road compared to adjacent parts of the roads. Ground beetles, grasshoppers, spiders, mice, shrews and bats can use a green bridge effectively when species-specific habitat elements are present on the bridges especially when these elements are connected to the corresponding habitats in the neighbourhood of the road. There was a general trend to more open-habitat adapted species on the overpasses even when they lie within forests. Statistical analyses, which was possible with the data of green bridges and larger mammals only (20 buildings, intensive frequentation), showed that especially width and age and to a lesser extent position were of positive influence on the use of the bridges. By contrast, dense canopy, traffic noise, the number of gravel roads, intensity of human use and nearby buildings lessen the frequentation of the bridges. For the effectiveness of wildlife passages it is important to choose the right target species, to develop habitat structures on, under and near the passageways which strongly meet the habitat requirements of the target species and to avoid as much human disturbances as possible.