KLEEFSTRA R, BIJLEVELD AI, VAN DIJK A-J, VAN ELS P, FOLMER E, VAN TURNHOUT C & VAN WINDEN E (2021) Wintering and migrating Eurasian Curlews Numenius arquata in the Netherlands: trends in numbers and distribution since the 1970s. LIMOSA 94 (1): 44-57.

No less than 25-50% of the world population of the Eurasian Curlew uses the Netherlands as a moulting, staging or wintering area. In this article we describe how the numbers of non-breeding birds have changed over time since the 1970s, based on the national monitoring scheme for waterbirds that contains high tide roost counts in the Dutch Wadden Sea and southwestern Delta, inland monitoring of fresh water systems such as lakes, swamps and rivers, midwinter counts, inland wader surveys and night roost counts. Since the mid-1970s the numbers of Eurasian Curlew in the Netherlands have increased, although this growth levelled off in the last ten years (Fig. 1). Numbers increased in all seasons (Fig. 2). At the end of the 1970s the seasonal maximums reached approximately 105 000-125 000 birds. In 2000-10, maximums of 175 000-200 000 birds were quite common. Since then, the seasonal maximums decreased to 150 000-175 000 Eurasian Curlews. Numbers of overwintering Eurasian Curlews increased in almost all regions in the Netherlands (Fig. 3). The largest number of birds was found in the Wadden Sea. The Dutch part actually has the largest numbers of Eurasian Curlews of the whole international Wadden Sea (Fig. 4). Numbers have stabilized in the Wadden Sea, which actually is the reason why the Dutch wintering population has stabilised. In the southwestern Delta, where the numbers are on average about a quarter of the numbers in the Dutch Wadden Sea, the increase of Eurasian Curlews only started around the turn of the century. Here numbers are still increasing. Inland, the numbers are only a fraction of those along the coast. Numbers increased in areas near large freshwater bodies such as rivers and lake IJsselmeer. In other inland areas numbers have been stable over time. It was difficult to make a comparison of Eurasian Curlew numbers on inland night roosts between 1982-83 and 2018- 19. Numbers varied a lot between roosts, and counts were often incomplete (Fig. 5). Maximum numbers on individual roosts were slightly higher in 1982-83, while average numbers were lower, but these differences were small. We suggest that total numbers of Eurasian Curlew in the Dutch Wadden Sea and the southwest Delta mainly increased due to favourable foraging circumstances. Benthos monitoring data show a good supply of prey species such as Soft-shelled Clam, Ragworms and Lugworms (Fig. 8). Instead, inland numbers and distribution did not change much.

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