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GERRITSEN GJ (2021) The breeding biology of the Eurasian Curlew Numenius arquata in West-Overijssel. LIMOSA 94 (1): 19-29.

With about 5000 breeding pairs, the European significance of the Netherlands for breeding Eurasian Curlews is modest, but regional densities are of European significance. This ongoing study started in 1982 in the western part of the province of Overijssel, one of the Dutch core areas for breeding Eurasian Curlew. During the first survey in 1982-83 439 pairs were found on 90 km2, an average density of 5 pairs/km2. In the 10 km2 core area the density was even 10 pairs/km2 . The majority of breeding pairs bred on grasslands of dairy farms. The average start of egg laying was April 10 and the average hatching date was May 13. In 1983-2020 the population decreased with 65%. Until 2010 the average yearly decline was 2.8% but this increased to a yearly decline of 10.1 % in 2010-20. 459 chicks were ringed of which (since 2000) 99 were colour ringed. The adult apparent survival of 0.93 was comparable to recent studies from abroad. In most years the population fails to achieve the required minimal reproduction of 0.39 fledglings, mainly as too many pairs fail to reproduce. Insufficient reproduction is the key factor for the decline of the Eurasian Curlew in the study area, with an average nest success of only 37% (Mayfield). In the 1990s agricultural practices were the main cause of nest failures, but nowadays most nests are lost to predation. Camera observations proved that Red Fox Vulpes vulpes and Carrion Crow Corvus corone are the main egg predators. Most chicks grow up in regrowing grasslands after mowing. In this monotonous habitat chicks are easy to find for predators such as Common Buzzard Buteo buteo. They seem the main predators of chicks during daytime based on observations of adult Eurasian Curlews mobbing predators. Parental care was provided by both parents in 88% of the families. In the remaining 12% only the male guarded the chicks (which were, on average 2.5 weeks old at that time). Other problems for Eurasian Curlews in the study area are grassland deterioration, low water tables, too early, too fast and too frequent mowing of grassland and intensified traffic on former dirt roads. Eighty percent of the resighted chicks returned to the study area to breed, with an average dispersal distance of 3.8 km. Two chicks dispersed abroad, 120 km northeast to Germany and 600 km to Denmark. There is still a future for a viable Eurasian Curlew population in the study area because of (1) a high adult survival rate of 0.93, (2) 80% of chicks returning to their place of birth, and (3) nesting success can be doubled by electric fencing. Chick survival might be the remaining factor limiting population recovery

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limosa 94.1 2021
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