Habitat requirements of Orthetrum coerulescens and management of a secondary habitat in a highly man-modified landscape (Odonata: Libellulidae)


Due to the destruction of its primary habitats, the West Palaearctic libellulid Orthetrum coerulescens has suffered much decline in central Europe. However, at the regional scale it has survived in a variety of secondary habitat, such as draining ditches. In order to find adequate measures for its conservation and promotion, habitat use and habitat recognition of O. coerulescens were investigated by description and experimentation at fenland ditches in a small nature reserve in the Swiss Plateau. This breeding habitat, which harbours a viable population, had been restored and maintained for 25 years. The most densely populated sites comprised small ditches between 40-70 cm wide, with rather sparse vegetation of narrow-leaved plants and that had parts of the water surface uncovered; the peaty, mud ground was partly overgrown with submerged pads of stonewort (Chara spp.). Water was mainly supplied by seepage springs with a mixture of local slow flow that were hardly recognizable and shallow sites, which were used for oviposition. In hot summer spells the water temperature could exceed 30°C. Some freezing occurred in winter, but the mud was permanently ice-free. The development of the breeding population, which comprised more than 200 individuals in 2006, was followed over two subsequent years. My data indicate that conservation and promotion of O. coerulescens populations in small ditches can be achieved by relatively simple habitat maintenance, such as a rotational strategy of clearing ditches, using of small weirs to prevent or protract desiccation and annual cutting of the surrounding litter meadows.

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