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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Long-term occupation of traditional winter roosts by the Hen Harrier Circus cyaneus in the region of the Ammersee (Bavaria), and importance of the Ampermoos
Auteurs :	Christian Fackelmann, Auteur
Type de document :	Article
Dans :	Ornithologischer Anzeiger (50(1) JUL 2011)
Article en page(s) :	43-60
Résumé :	Steadily growing numbers of Hen Harriers have been observed at the Ammersee (south-west of Munich, Upper Bavaria, Germany) since 1968/69. The first roost was located in Ampermoos (SP 1) at the northern end of the lake in 1988; others in the Ammermoos (SP 2) and Herrschinger Moos (SP 3) were detected in subsequent years. Some further roosts were only occupied in single seasons. In the wider region roosts were located in the Leutstettener Moos and in the Loisach-Kochelsee-Moor. Since the beginning of 2002 monthly synchronized counts have been made at the Ammersee roosts between October and April. Throughout this period the main roost in the Ampermoos has been intensively monitored. The importance of this roost grew steadily over the eight winters and now hosts almost 90% of the birds in the region of Lake Ammersee. The monitoring revealed unusually high numbers with a daily maximum of 110 individuals in the Ampermoos and 119 individuals at the Ammersee. This makes the Ampermoos by far the most important roost in Bavaria, comparable with the Federsee in Baden-Wurttemberg.The presence of Hen Harriers is dependent on the weather. They leave the area when the ground is snow-covered for several days, but return immediately with the beginning of thaw. Where the roosting communities move to in times of snow is still unknown. Observations of solitary birds and small groups in the wider region, in times of snow-cover, roosting in situ at unusual locations, indicate that they disperse to exploit hunting grounds that remain productive. The roosts in the area of the Ammersee are in loose reed- or fen-meadow vegetation. The catchment area extends at least 15 km from the roosts.Arrivals at the roost are spread over three hours or more, whereas the morning departure starts on average 25 minutes before sunrise and lasts 36 minutes. When the congregations are unusually high the departures can last over one hour. 85% of the Hen Harriers leave to south or west to preferred hunting grounds in the higher pasture lands between the Ammersee and the river Lech. Mown fen-meadows close to the roost-site form an important component as a meeting and resting place within the harriers' winter habitat. Several birds had gaps in their flight-feathers, pointing to moult activity in winter.Further, as yet undetected roost sites almost certainly exist in southern Upper Bavaria. The expanding wild boar population, recreational activities and dogs pose an increasing threat to the existence of the roosts. The birds' reaction to disturbance by humans and particular animals is to change the roost site, while small roosts are given up.As well as these threats through human and animal disturbance, the significance of potential predators and the influence of other bird species is illustrated. Possibilities for long-term upgrading and protection of the Ampermoos as a Harrier habitat are described. Future work and questions to be answered are outlined.

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