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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Population trend, breeding biology and reproduction success of the Curlew Numenius arquata in the fens of Mettenbacher and Griessenbacher Moos near Landshut, Bavaria
Auteurs :	Maria Engl, Auteur ; Franz Leibl, Auteur ; Klaus Mooser, Auteur
Type de document :	Article
Dans :	Ornithologischer Anzeiger (43(3) December 2004)
Article en page(s) :	217-235
Résumé :	1. The breeding population of the curlew in fens (wet meadows) in the Isar river valley northeast of the Bavarian city of Landshut (Mettenbacher Moos, Griesenbacher Moos) has been documented annually since 1986. In 1999 and 2003 additional data regarding the breeding biology, particularly breeding success, was collected as well. 2. In contrast to other curlew breeding localities in Bavaria, the research area exhibited a slight population increase. A preliminary maximum was reached in 2002 and 2001 with 28 breeding pairs. In recent years, between 1999 and 2001, population density values ranged between 0.35 and 0.38 breeding pairs/10 ha. Maximum values of 4.2 bp/10 ha were reached in nutrient-deprived ecological compensation areas. 3. Between 1999 and 2003 the study encompassed a total of 57 nest sites. 81% of these were located in agricultural meadows, 16% in arable fields and 3% in areas, which have been taken out of production. Extensive meadows with sparse, low growth were found to be especially attractive nesting locations (80% of all broods in grassland). A few breeding pairs demonstrated fidelity to a specific nesting site for at least two successive seasons. The selection of a nesting site was inhibited neither by the occurrence of neighbouring bushes nor by the nearby existence of occupied carrion crow nests. 4. Clutch sizes were determined for 38 nests. 84% of the nests had four, 13% had three and 3% had five eggs. 5. In the 2002 and 2003 seasons thermologgers were employed to help analyse breeding progress. The first eggs were laid in the second April decade. The majority of clutch losses occurred between April 24 and May 1. Renesting was the exception in this study area (observed twice in 2001, three times in 2002). In 2001 68% of the breeding pairs achieved no hatching or breeding success, 78% in 2002 and in 2003 the same held true for 85%. Hatching dates ranged between May 8 and 15. The brood-rearing period varied between 31 and 46 days. 6. Between 1998 and 2003 the average breeding success rate was 0.31 fledglings/breeding pair, a value not sufficient to guarantee continued survival of the population on its own effort. Exact data on hatching and breeding success in 2001 and 2003 are illustrated in Table 3. 7. Breeding success of the curlew in the study area is significantly influenced by the activity of terrestrial predators. In 2001 sixteen (= 62%) of the marked clutches were lost to predators. In 2002 and fourteen (= 67%) of the clutches provided with thermologgers were preyed upon by nocturnal predators. Remarkably, not a single clutch was taken by carrion crow or by any other avian species. Observations of eggshell fragments and tooth marks lead unequivocally to identification of the red fox (Vulpes vulpes) as the nest predator. 8. Not a single clutch was lost to agricultural practices in the 2001 and 2002 seasons. This has come as the result of species protection efforts, which have been carried out in the area for a number of years. In the study area more than 100 ha of grassland are currently under contract through the Bavarian Conservation Programme. In addition, approximately 120 ha have been purchased for conservation purposes.

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