Navàs, F. y Rosell, C. Improvement of mitigation measures on an existing road crossing a wetland area proposed for the inclusion on Nature 2000 Network (Catalonia, NE Spain). Habitat Fragmentation due to Transport Infrastructure & Presentation of COST action 341 products. Bruselas: Infra Eco Network Europe (IENE). 2003.
The Aiguamolls de l’Empordà Natural Park is a wetland area of Catalonia (north-eastern Spain) proposed for the Nature 2000 Network as a Site of Community Importance. On year 2000, a local road crossing this Natural Park (and a Natural Reserve), with some 25.000 vehicles per day, was converted into a motorway. The motorway was fenced and, for the first time in Catalonia, specific wildlife passages were built in order to minimize fauna impact, especially for amphibian, carnivores (polecat, Mustela putorius, and otter, Lutra lutra) and ungulates (wild boar, Sus scrofa, and fallow deer, Dama dama)
During spring and autumn of 2001 a study was carried out, on the 2,2 km stretch crossing the Natural Park, to assess the effectiveness of fauna passages, to identify black spots of fauna casualties and to make some proposals to enhance the use of these structures by fauna and to improve other mitigation measures. 17 fauna passages and adapted drainages were checked for a week in each season by using a marble powder substrate to register animal tracks and infra-red photographic cameras. Identification of black spots was made by collecting all the vertebrate carcasses found on the road during one month each season.
The fauna passages were intensively used by almost the whole terrestrial animal groups in the area. There were identified 15 wildlife species, plus some birds that also cross these structures. Polecat was identified in one structure (with a diameter of 0,8 m), otter in three adapted drains and wild boar in the two wider structures (10 and 11 m width each one). Fallow deer don’t use these structures (probably due to height that it is 2 m as a maximum).
Over the road, there were found 117 carcasses of a minimum of 29 vertebrate species. The most affected group were birds (53% of total mortality). Some of the species identified are catalogued as species of Special Interest in Spain: tree frog (Hyla meridionalis), ladder snake (Elaphe scalaris), purple gallinule (Porphyrio porphyrio), Savi's warbler (Locustella luscinioides) or Great reed warbler (Acrocephalus arundinaceus). There were found also some birds that had died after collision with glass acoustic screens installed to reduce nuisance to nesting birds, despite the use of adhesive bird of prey silhouettes which, it was hoped, would frighten the birds away. This measure was proved to be completely inefficient.
Some of the proposals made to enhance use of passages and to reduce fauna casualties include:
- Installation of an opaque barrier, close to the perimeter fencing, to prevent amphibians and reptiles crossing over and to guide them to the passages.
- Lengthening the lateral platforms, that provide a dry zone in case of flooding, on four adapted drainages, that were not built on the ancient structure when upgrading the road. Also it is proposed to construct ramps that must facilitate the access of animals to these platforms.
- Planting of vegetal screens to force birds to fly higher.
- Adhesion of vertical strips on the transparent acoustic screens, to make they visible to birds and to avoid their collision.
Assessment of applied measures effectiveness, when the road is already in use, is a fundamental element to improve future design of measures and also to correct detected deficiencies and to reduce the impact of the road on the fauna.
Palabras clave: Connectivity, Enhancement measure, Fauna, Fauna passage, Habitat fragmentation, Motorway, Wetland
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