Use of the nonspecialised structures as a wildlife passages Lyulin Motorway Bulgaria

Most of the motorways in Bulgaria were built before the implementation of EC regulations related to the ecological corridors’ preservation. As consequence a lot of them are barriers for the wildlife movements, moreover when they lie in important natural areas, connecting distant populations. One such an example is the Lyulin Motorway. Because of the rough mountain terrain the road pass through numerous infrastructure facilities (26 viaducts, 3 tunnels, culverts), which occupy 30% of its entire length. The potential use of the structures by the wildlife has not been investigated yet but their existence means that the motorway is not a continuous impenetrable physical barrier.

However none of these structures is specially designed as a wildlife passage; a lot of them are not suitable due to their dimensions, position, technical implementation and cover or because of an enhanced human presence and hunting nearby.

Three-months camera trap monitoring and snow and mud tracking were carried in order to evaluate the use of the passing structures by the middle-sized and big mammals and to estimate what the issues are. Two tunnels (Lmean=400m), 6 viaducts (Hmax=10m, Lmax=476m, Lmin=81m) and 4 culverts were investigated in the segment where the motorway runs through habitats with high quality, part of the big carnivores’ biocorridors on national level.

We found that the middle-sized mammals – stone marten (Martes foina), red fox (Vulpes vulpes), wild cat (Felis silvestris) – use all types of structures. In all cases the passes were one-way; a sign that the animals use several structures or cross the roadbed.  Hares (Lepus europaeus) and roe deer (Capreolus capreolus) were registered predominantly on the tunnels (Fisher Exact Test, p=0.045) which serve as “green bridges”. We did not found any evidences for big animals crossing like red deer (Cervus elaphus), wolf (Canis lupus) or bear  (Ursus arctos) although their presence in the vicinity. It could be due to the short period of the investigation or because of the human presence. During field visits we found also that the fence (the only fragmentation mitigation measure present) was in a poor condition and hardly promote the use of the passing structures. On the other hand the structures by them self are not well integrated in the surrounding landscape, miss vegetation and natural cover, the human presence is considerable, there are roads, serious erosion and illegal landfills. All these factors stultify the great permeability of the segment – between 27,5% and 43,4% for the different animals groups, while it vary between 3,1% and 12,1% for Hemus and Trakiya motorways (Zlatanova, 2010).

The study could be used as a model evaluation for the old motorways permeability in Bulgaria and contribute for the mitigation of the habitat fragmentation in the cases when potential passing structures exist but are lacking the appropriate design and landscape integration.

motorways permeability, crossing structures, habitat fragmentation, mammals, camera traps.