Verrassingen bij broedende Drentse Wilde Zwaan Cygnus cygnus in 2010-2011
Drentse vogels , Volume 25 - Issue 1 p. 34- 40
. For the sixth and seventh consecutive year in 2010-11 the only breeding pair of Whooper Swan in the Netherlands was again breeding in a swampy area in the brook valley of the Wapserveense Aa in SW-Drenthe near Steenwijk (52o50’N, 6ol2’E).The cygnets were raised in swampy grasslands in a polder with ditches, small ponds and vegetation dominated by grasses, sedges and water horsetail. Except for the breeding female the adults predominandy were feeding on grasslands of ryegrass. In both years 3 eggs were laid. Surprisingly in 2010-11 the breeding pair of 2005-09 was replaced. The new female was an Wapserveen raised young of 2007 (darvic ring HNI) and only three years old in 2010. According to its behaviour also the male (no ring) was replaced. The old breeding pair was last seen in March 2010. Between 19 April and 23 May 2010 the female was breeding for 33 days. Ten days after hatching one cygnet disappeared and the two left over were reared for more than a month in the swampy polder. On 5 July the breeding pair moved to the small lake of Eesermeer near Steenwijk (Fig. 1), as was the case in 2006-07. The journey started at 7h30 with only one cygnet and after 5,5 hours of walking trough grasslands, corn fields and along ditches with some steep slopes, crossing two roads and swimming in the brook Wapserveense Aa, the family finally reached their destination. The couple and the cygnet stayed in Eesermeer for 15 days when all swans were disappeared. Surprisingly enough three days after the journey the second cygnet was discovered in the swampy polder. Apparently it had missed the journey. After one day it was not seen again. As was suggested in 2006 the move in 2010 presumably was triggered (and in hurry) because the polder started to dry out. In comparison with 2006-07 the journey in 2010 was started at least 19 days earlier when the cygnets were 43 days old, while in 2006-07 their age was 62-77 days. In 2011 breeding starts on 21 April at a new nest and after a period of 34 days 2 cygnets were hatched. In contrary to 2010 the cygnets stayed in the swampy polder till September. Most likely this had to do with the high water level during the wet summer month. One cygnet could fly on 7 September, but the other remained well behind in growth. This already became clear when both cygnets were ringed at 26 July. In mid September the wings were still very short (c. 20 cm) and it was only able to run and swim. After 16 September this cygnet was not observed anymore. Between 7 and 30 September both parents were moulting their feathers and were unable to fly. They stayed as a family in open waters of small pools and ditches and often hided themselves in the swampy vegetation. This was the first time that the parents were moulting at the nesting site (thanks to the high water level). In 2006-07 they moulted in Eesermeer. In 2007-11 the Whooper Swans has produced a total of 25 eggs. Sixteen cygnets were hatched and seven of them were able to fly. The two (unmarked) young of 2006, were certainly regularly observed in Drenthe till 2009. Of the four colour ringed cygnets in 2007 two are found dead (24-01-2008 and 27-02-2010), one is the breeding female in 2010-11 and the forth one was irregular observed in Drenthe in 2008-10. In May-September 2011 this bird stayed ip a wetland near Beilen, Drenthe and in mid September it was moulting wing feathers. Between April and September 2007-11, when there are hardly migrating or wintering Whooper Swans in the northern part of the Netherlands, every year at several sites mostly solitaire Whooper Swans of unknown origin were observed. The Whooper Swans of Wapserveen and their offspring most likely shall have a fair share of these observations (sometimes confirmed by rings). It is suggested that Whooper Swans are able to settle as breeding birds at more sites in the Netherlands.
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