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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	The Wryneck Jynx torquilla in Denmark, with special reference to the breeding population at Borris Hede 1970-2001.
Auteurs :	Egon Ostergaard, Auteur
Type de document :	Article
Dans :	Dansk Ornitologisk Forenings Tidsskrift (97(4) 2003)
Article en page(s) :	303-311
Langues:	Anglais
Résumé :	The breeding population of Wryneck Jynx torquilla has decreased dramatically in Denmark during the last three decades. Maybe only 75-100 pairs breed annually (Grell 1998). At Borris Hede in the western part of Jutland the population has been surveyed since 1970, when a nestbox project began. The number of Wryneck boxes gradually increased to a maximum of 120 in 2001. Borris Hede is a 47 km2 military training field (see Table 1 for habitat distribution). The first boxes were made of dugout tree trunks, while later boxes were produced from eternit, a very durable material. The boxes were put up about 1.5 m above the ground, mainly in solitary trees near dry grazing areas. In the period 1975-1987 the annual number of broods was about 10, with a maximum of 13 in 1978 (Fig. 2). Since 1988, however, only 2-6 broods per year have been found. This trend is similar to the development in the number of ringed birds at four Scandinavian bird observatories, Falsterbo (S), Ottenby (S), Christianso (DK) and Blavand (DK), as well as the total number of Wrynecks ringed in Denmark (Zoological Museum, University of Copenhagen) and the number recorded in the annual Danish Bird Reports (DOF BirdLife Denmark), see Fig. 4. At Borris Hede the Wryneck has bred in 73 different nestboxes during 1970-2001 (Fig. 3). Of the total of 181 broods, 102 (56%) were found in boxes not used neither in the preceding nor the following year. The fact that the number of Wrynecks breeding in nestboxes increased quickly during 1970-75 may indicate a shortage of natural nestholes. The later decrease probably reflects the general trend in Denmark, since no changes detrimental to the Wryneck - in habitat characteristics or otherwise - seem to have occurred in the study area. Most pairs today breed in areas with sandy and poor soils, with 35% of the Danish population occurring in an area of Jutland covering only 5% of the country. In areas with clayey soils the Wryneck is virtually absent. No obvious relationship could be found between the decreasing numbers in Denmark, or at Borris Hede specifically, and meteorological statistics like the annual mean temperature, precipitation, or number of sun-hours since 1970.

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