VAN HORSSEN P & KLEEFSTRA R (2022) Roosting Little Egrets Egretta garzetta on the Dutch Wadden Sea island Schiermonnikoog. LIMOSA 95 (2): 105-112.

In the special issue of Limosa on the Wadden Sea in 2009, an overview article described the increase of Little Egrets in the Wadden Sea. The authors mention a Little Egret roost on the island of Schiermonnikoog, but at that time only anecdotal information was available. Here we describe the number of Little Egrets on Schiermonnikoog in 2000-2020, based on roost counts at the Westerplas and diurnal high tide roost counts (Fig. 1).
Maximum numbers were present in August, September and October, with respectively 39, 86 and 87 individuals at the roost and 34, 77 and 32 individuals during the high tide roost counts (Fig. 2). Lower numbers were encountered from December to May, with a maximum of 0-2 individuals at the roost and 0-10 individuals during high tide roost counts. Annual numbers of Little Egrets on Schiermonnikoog varied, with a peak in 2008, a dip in 2013 and a gradual increase thereafter (Fig. 3). This pattern is likely the result of severe winters in 2009-2011. Most egrets arrive at the roost 10 minutes before sunset to about 20 minutes after sunset (Fig. 4). The large number of Little Egrets roosting on Schiermonnikoog cannot be explained by the small number of Little Egrets breeding in the Dutch Wadden Sea. Based on resightings of colour-ringed individuals it is likely that these Little Egrets partly originate from breeding areas in the southwest of the Netherlands. The eastern part of the Wadden Sea, where Schiermonnikoog is situated, might be an attractive foraging area for Little Egrets due to an increase in Pacific Oyster (Crassostrea gigas) and Blue Mussel (Mytilus edulis) beds.

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