OUWENEEL GL (1971) The occurrence of the Barnacle Goose Branta leucopsis in the Hollands Diep-Haringvliet area. LIMOSA 44 (3): 84-101.

I. The Barnacle Goose has increased strongly as a winter visitor in the Netherlands since the beginning of the 1950's. Besides the haunts in Friesland the Hollands DiepHaringvliet area in the delta is an important wintering-place for the species. II. The Hollands Diep-Haringvliet is about 55 kilometres in length; its width varies from about 2 kilometres near Moerdijk till more than 4 kilometres near Hellevoetsluis (Fig. 1). As a part of the Delta-works the river was closed from the Northsea in November 1970. Before the closure the river was under the influence? of the tides. At low tide a lot of banks were left dry along the shore as well as in the river. Important banks are the Slijkplaat, the Ventjagersplaten and the Sasseplaat. After the closure about 70% of the banks disappeared permanentely under water; only parts of the banks are left dry now irregularly. The Hollands Diep-Haringvliet is surrounded by polders. North of the river there are two large areas with grasslands, the Oude Land van Strijen (about 1200 ha) and an area on Putten (about 1500 ha). South of the river only one large area with grasslands is situated, the Haagse Beemden (about 1500 ha). The small grasslands outside the dikes are of great importance for the Barnacle Geese. Before the closure of the river every winter these grasslands were flooded irregularly. III. Before the 1950's the Barnacle Goose was an irregular and scarce winter visitor. In the severe winter 1946-1947 the species was numerous on Goeree. IV. The first geese arrive in the last days of October in the area with a further increase in the course of November and December. The normal winter population varies between 4000 and 8000 birds. Under the influence of cold waves from northern wintering-places other Barnacle Geese arrive in the area. Under these circumstances numbers vary from 10.000 till 15.000; up till now the maximal number counted at one date in the area is about 20.000 (on 22-2-1969). The last few years hundreds of geese stay on Overflakkee up to and including the third april-decade: 5-5-1971 was the last date on which a flock of importance was observed (90 geese). The principal haunts are the Oude Land van Strijen (Fig. 1, region 1), the St. Antoniegorzen (8), Tiengemeten (9), Westerse Gorzen (11), Westplaat (13) and Scheelhoek (14). Almost all the grasslands in the area are visited by Barnacle Geese, however, some of them irregularly and under influence of cold when the numbers have increased. The birds are visiting their haunts with often changing numbers. The principal roosts are the Ventjagersplaten (region B and C) and the Slijkplaat (region A); other roosts are situated along the northern bank of the river (region D and E). As other geese the Barnacle Goose is feeding at day-time and spending the night at the roosts. Feeding at night, not only with the moon shining, was established in region 1. Some characteristics in behaviour are mentioned. There are some indications that adaptions to human activities occur. On GoereeOverflakkee flocks of geese may feed at some tens of meters distance from busy roads and villages. With the exception of the long and severe winter 1962-1963 the Barnacle Geese stay also in the area in periods with ice and snow. In the eastern part of the area the species generally visits its haunts together with Whitefronts and Bean Geese; in the western part flocks of only Barnacle Geese are in the majority. The geese which feed in the eastern part of the area have their roosts on the Ventjagersplaten; the geese from the western part roost on the Slijkplaat. It seems that the birds do not always visit the same roosts. Other roosts (regions D and E) seem to be of less importance. V. About 10 till 20% of the world population of this species winters in the area; during cold waves up to 50% of the world population may stay here. The closure of the Haringvliet resulted in the reduction of the tides. Several dangers are threatening the area. In november 1970 a number of haunts were protected by law (Fig. 1, the regions 2, 3, 7, 9, 10, 11 and 13). The future for the regions 1 and 8 is still uncertain. The most important haunt, the Westplaat, was ploughed just before the effect of the protection. In 1970-1971, the first season after the closure of the Haringvliet, the number of the wintering Barnacle Geese reached their usual level. Barnacle Goose Branta leucopsis

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