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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Systematic counts of Common Cranes Grus grus on autumn migration in the years 1987-2009 in the area of Marburg/Lahn, central Hesse, Germany
Auteurs :	Martin Kraft, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (131(2) 2010)
Article en page(s) :	147-154
Résumé :	The Marburg area has always been on the classical migration route of the Common Crane, but systematic counts of migrating birds have only been performed since 1987. Results are presented in this paper. From the roof of the biology building, Philipps-University, Marburg (about 380 m a.s.l.), as well as from two other hilltops near Marburg (300 and 390 m a.s.l.), which offer a good view all around, migrating cranes were counted at a width of some 80 km using binoculars and strongly magnifying telescopes. From 1987 to 2009 the number of cranes increased continuously. While in 1987 about 20,000 cranes passed the area of central Hesse, the number increased to 150,300 in 2009. The biggest ever count was registered in autumn 2008 when more than 175,000 cranes crossed the Marburg area and surroundings in central Hesse. The average flock size, which varied between 126 birds in 1995 and 482 birds in 1999, and the number of days with crane migration also increased from a minimum of 12 (1989) to a maximum of 53 (2005). In addition, mass migrations, which occurred on 1 or 2 days in the early years, occurred on at least 7 days during the last years. On 21(st) Oct. 1997 about 33,000, on 27(th) Oct. 1997 about 25,000, on 14(th) Oct. 2005 at least 35,000 and on 3(rd) Nov. 2006 about 81,500 migrating cranes passed in only 6 hours. Mass autumn migration occurred mostly on clear days and more or less strong winds from easterly or north-easterly directions (anticyclonic conditions). Although the numbers of cranes significantly increased during this long-term study, the numbers of resting cranes did not change. The biggest ever resting number was registered on 3(rd) November 2006 when at least 25,000 cranes stayed for three days in the Marburg area. In autumn 2008 and 2009 about 240,000 cranes crossed Germany, up to 73 % of this total number passed the Marburg area in 2008. Hence the total number of cranes using the western flyway appears to be well-corroborated. Simultaneous counts of visible crane migration in addition to the counts at their resting places in Germany and other countries covering the entire migration corridor are encouraged as an additional tool of monitoring the flyway population.

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