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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Reduction of habitat quality for wintering White-fronted Geese Anser albifrons induced by middle-tension power lines (25 kV).
Auteurs :	Hauke Ballasus, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (123(6) 2002)
Article en page(s) :	327-336
Résumé :	This study investigates the possible effects of two middle-tension power lines on the grazing intensity and the patterns of grassland use by wintering White-fronted Geese. The traditional foraging site is part of a nature reserve in the foreland area of the lower Rhine region, North-Rhine Westphalia (FRG). It consists of 14 different pastures and has a size of 56 hectares. Single pastures are differently exposed to a road and two 25 kV power lines crossing the area nearly parallel in a distance of about 300 m. By nearly daily goose counts during the wintering periods 1996/97 to 1998/99, the geese frequency on single pastures and the distances of flocks to the road and the power lines were examined. Counted goose flocks were plotted exactly in German Basic Maps (Deutsche Grundkarte 1:5000). A square net (40X40 metres) over the study area was used to quantify the median density of each goose flock and the grazing pressure on different parts of the area. Data were also analysed on pasture field level to quantify the patterns of field use. Supplementary the sward height in various distances to one of the power line was determined after repeated goose visits of one selected pasture. The data show that: 1. The grazing intensity representing an observation period of three years was strongly reduced for pastures between and beneath the power lines. 2. Main patterns of field use varied strongly between single pastures: Pastures near to the power lines and local road were used later during wintering periods, geese frequency was lower and the time period in which grazing took place was shorter in comparison to pastures of greater distance to the disturbance factors. 3. For single pastures crossed by the power lines a significantly reduced grazing intensity was evident up to a distance of 40-60 metres. 4. After repeated grazing of a selected pasture the sward height below the wires was significantly higher than in 50 meters distance to the power line. 5. The impact of the road varied between pastures and wintering periods. A reduction in grazing intensity was found up to a distance of 80-160 m.

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