engleski

Bears coping with Croatian highways.

Habitat connectivity is the single most important factor determining its quality. On the other hand, transportation routes are the single strongest fragmenting factor of the habitat. In Croatia there are over 1000 km of fenced highways, with 319 km within the brown bear range. Due to the topography and to the specific mitigation measures 43.6 km (13.6%) are permeable for bears and other ground dwelling animals, as the highway is passing through tunnels, over the viaducts or bridges, or under green bridges (N=6) as specifically constructed wildlife crossing. However, some bears overpass the wire mesh fence and do get on the highway route resulting in up to 10 bear mortalities per year. We used GPS telemetry data obtained from 4 male bears captured and equipped with radio-collars (VECTRONIC) within 2 km from the highway, to identify locations and frequency of crossings. To be able to determine as close as possible the location where the bear crossed the highway, we used the virtual fence function implemented in collars to define a buffer of 1000 m on each side of the highway. Within the buffer, spatio-temporal resolution of bear trajectories increased because the collar acquisition rate switched from one localization per hour to one every 15 minutes. During 167 days (May 20th to November 3rd) we documented 69 total crossings with all the bears crossing the highway more than once (Range=4-26, Mean=17.3). The average distance that bears walked in 15 minutes when actively moving (>100m/15minutes) was 228 m (median) or 281 m (mean). Therefore, we created a 200 m buffer around all the structures that bears could have used to walk above or under the highway route and we analyzed high-resolution steps (lines between two consecutive GPS locations acquired every 15 minutes) aiming at discerning between bear crossings occurred through proper structures and those occurred through fence overstepping. After all, we assigned 44 bear crossings to spots where the highway is in tunnel, 7 where it is on the viaduct and only two possible crossings over the fence. We conclude that bears do use the available objects available as crossing structures in most cases (96%) and that the enforcement of the fence could prevent the remaining unwanted situations of bears on the tracks of the high-speed highway.

Brown bear, Croatia, highways.

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