KLEEFSTRA R & SCHEKKERMAN H (2019) Curlew Sandpipers Calidris ferruginea on high tide roosts near Westhoek, central part of the Dutch Wadden Sea. LIMOSA 92 (2): 65-73.
The Curlew Sandpiper Calidris ferruginea is a scarce species in the Dutch
Wadden Sea, with short migration peaks during spring (May)
and autumn (July-September). Due to these short peaks,
the population cannot easily be assessed accurately using
the regular monthly counts of waders on high tide roosts. In
order to get a better estimate of the migrating numbers of
Curlew Sandpipers in the Dutch Wadden Sea during autumn
migration, we conducted weekly counts on high tide roosts
along the Frisian Wadden coast, over a stretch of 11 km from
Koehool to Zwarte Haan, in the period July 2001-September
2018. The most important roosts are the salt marshes of
Westhoek and Zwarte Haan (Fig. 1). In 2001-10, counts were
largely conducted in the period mid-July to mid-August,
whereas in the years 2013-18, counts were largely performed
from the beginning of July to the beginning of September.
No counts were conducted in 2011 and 2012.
The maximum number of Curlew Sandpipers during the first
peak of autumn migration (end of July-beginning of August)
were between 2110-8000 individuals (Fig. 2). The maximum
numbers of Curlew Sandpipers during the second peak of
autumn migration (end of August-early September, years
2013-18) were always lower than the first migration peak
(740-2980 birds; Fig. 2), with two outliers in 2013 and 2016.
These two outliers were years with a high breeding success,
arguably due to Lemming peak years, likely with high
numbers of migrating juveniles. The trends of our weekly
counts clearly do not match with the regular monthly counts
for the months July, August and September (Fig. 4). In fact,
the average number of Curlew Sandpipers counted during
these weekly counts are higher in all three months (Tab.
1). This difference can be explained by the fact that during
monthly counts the short migration peak easily can be
missed. No juveniles were counted in July and early August,
while from mid-August to mid-September the proportion of
young birds was 50% to almost 100%.
The high tide roosts near Westhoek, in the central part of the
Dutch Wadden Sea, have become important stopover sites for
Curlew Sandpipers. It is one of the species, just like Common
Shelduck Tadorna tadorna, Pied Avocet Recurvirostra avosetta
and Common Redshank Tringa totanus, of which numbers
declined in the German Wadden Sea in summer and autumn,
while numbers in the (central part of) the Dutch Wadden Sea
have increased. High densities of Mud Shrimps Corophium
volutator can be a potential reason for this development.
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