DIJK J VAN & WASSINK A (1980) The course of the visible spring migration of some waders along the coast of Noord-Holland and Zuid-Holland. LIMOSA 53 (4): 109-120.

In 1972 the "Club van Zeetrekwaarnemers" was founded with the aim to coordinate the collecting of quantitative data on the passage and occurrence of seabirds along the coast of the Netherlands. Socalled hourly-total cards are used for data-recording (de Miranda 1978). In 1974-'78 more than 5000 cards referring to March-June have been filled in and returned by observers (table I). Most data were gathered near Scheveningen and Noordwijk (Zuid-Holland) and on the Hondsbossche Zeewering (Noord-Holland) about 75 km north of Scheveningen. The seasonal patterns in 1974-'78 are shown in figure 1-10 and summarized in figure 12. The passage in the course of the day is shown in figure II. For many species (e.g. Grey Plover, Curlew, Bar-tailed Godwit) strong passage along the Dutch coast coincides with high numbers in the Delta area and the Waddensea. Other species (e.g. Knot, Redshank) have a peak in numbers which is not accompanied with high numbers in the Waddensea. Probably these species move very fast in northeastern direction. According to Dick (1979) all Knots passing in May along the Dutch coast, started their non-stop flight in Vendee (France) and are on their way to the German Waddensea.
      Remarkable differences were noted between seasonal patterns along the coast of Noord-Holland and Zuid-Holland. Some species and especially those migrating in March (Dunlin, Curlew), showed peak numbers along the Hondsbossche Zeewering. Some other species and especially those migrating in May (Ringed Plover, Redshank), passed in highest numbers along the coast of Zuid-Holland. The cause of these differences are obscure. Different populations are probably involved in species with a prolonged period of migration. Dunlins passing in March may belong to the Baltic population whereas birds passing in May should belong to arctic populations (cf Glutz von Blotzheim et al. 1975). Many Knots passing in April belong to the breeding population of Greenland and Canada and probably all Knots passing in May are on the way to the Taimyr Peninsula (USSR) (Dick 1979). Sanderlings passing in March and April may be of Nearctic ongm, whereas birds passing in May are going to Siberia (Prater & Davies 1978). High numbers of waders were recorded during periods with NNE-E winds: During and after front passage accompanied with drizzle and poor visibility (500-2000 m), very high numbers of Dunlins, Redshanks, Grey Plovers and Knots were recorded. On the other hand peak numbers of Ringed Plovers and Sanderling were observed during dry weather with good visibility. Common Ringed Plover Charadrius hiaticula Grey Plover Pluvialis squatarola Red Knot Calidris canutus Sanderling Calidris alba Dunlin Calidris alpina = Calidris alpina schinzii Bar-tailed Godwit Limosa lapponica Whimbrel Numenius phaeopus Eurasian Curlew Numenius arquata Common Redshank Tringa totanus Ruddy Turnstone Arenaria interpres

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