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Titre :	The breeding environment of the Corncrake, and the past, present, and possible future of the species in Denmark
Auteurs :	Ole Thorup, Auteur
Type de document :	Article
Dans :	Dansk Ornitologisk Forenings Tidsskrift (93(2) 1999)
Article en page(s) :	71-81
Langues:	Anglais
Résumé :	In the 19th and early 20th century Corncrakes Crex crex were widespread and common in hay meadows all over Denmark and, on a more limited scale, also in cultivated fields. The breeding population probably comprised at least 10-20 000 pairs. This estimate is obtained by comparing general statements relating to Corncrake abundance with statements about Redshanks Tringa totanus and Common Snipes Gallinago gallinago in available sources from 1800-1930 (Lange 1919, Heilmann and Manniche 1939, Palm 1988a, b, c), or by assuming that breeding densities in cultivated land, especially in permanent grass-land, were similar to present densities in Belarus, Estonia, Latvia and Lithuania (by 1992; Tucker and Health 1994, Green and Rayment 1996, Tucker and Evans 1997). The second method may underestimate the former Danish population to some extent, however, since the level of mechanisation and usage of fertilizers in Denmark at the turn of the century was much lower than the present level in Eastern Europe (Johansen 1986, Tucker and Evans 1997). During the present century the Corncrake disappeared almost completely as a breeding bird in Denmark, with probably only 25-100 pairs remaining in the early 1970s (cf. Dybbro 1976). During the last decade the species may not have bred every year, and the total population hardly exceeded 30 pairs in any year (Tab 1, with allowance for an incomplete coverage of the species). The population declines in Britain and in Finland were analysed by Norris (1945, 1947), von Haartman (1958), Green and Stowe (1993), and Green (1996). In both countries the decline was closely correlated with changes in agricultural practice. Everywhere in Europe most of the Corncrakes breed in hay meadows which, until about 125 years ago, were manually mowed in late July and in August. The main factors behind the decline of the Corncrake were the adoption of much earlier mowing dates and a more rapid mowing made possible by the introduction of mowing machines (see also Stowe and Hudson 1988, 1991, Schaffer and Munch 1993, Petterson 1993, 1994, Niemann 1994). The chronology of the decline of the Corncrake in Denmark is rather imperfectly known since descriptions in the literature are somewhat contradictory, but it appears to have occurred mainly from the late 1920s until the mid-1940s. As was the case in Britain (Norris 1947) the decline in Denmark probably varied regionally, because modern farming methods were introduced much faster on Sjaelland and Fyn, and near cities generally, than in the more remote parts of Jylland (Johansen 1985, Bjorn 1980. Corncrakes were declining near Copenhagen during the 1920s, when populations in other parts of the country apparently were still unaffected (Heilmann and Manniche 1939). In the early 1960s the Danish Corncrakes were primarily located in three river valleys in Jylland, Skjerna-deltaet, Varde Adal, and Rya Enge in Store Vildmose. Skjerna-deltaet was abandoned after extensive drainageand cultivation in the 1960s, and the early mowing in Varde Adal resulting from fertilization of hay meadows from the late 1960s onwards meant the disappearance of Corncrakes from that area too, in the early 1970s. In Store Vildmose several males were heard calling each year until 1983 (Nyrup 1994), but no Danish sites have had a regular occurrence since then. In the mid 1990s two projects were initiated with the aim to create "recovery areas" for breeding Corncrakes. In Store Vildmose parts of the meadows will be managed in a Corncrake friendly way, with provisions for the authorities to regulate the management in other meadow areas as well. These measures may permit successful breeding of Corncrakes in the area in the future. In Varde Adal a project named "Operation Corncrake" among other things provides funding for compensating farmers who agree to extensify their land use under contract with the county. However, in their present form these contracts are insufficient to ensure proper breeding possibilities or Corncrakes, so unless improvements are introduced, Corncrakes will probably never resettle in this area. The Corncrake almost disappeared from the Danish fauna at a time when no green NGOs or a Ministry of Environment existed. However, the country still has the obligation to protect this globally threatened species. The creation of grassland areas with appropriate management will almost certainly ensure that Corncrakes will reestablish viable breeding populations, and the requirements of the species are now sufficiently well known to implement such a management regime (Tab. 2). Nevertheless, the Store Vildmose project is the only measure taken so far to safeguard the future of the Corncrake in Denmark.

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