DIJK AJ VAN (2006) Whooper Swan Cgnus cygnus as new breeding bird in The Netherlands. LIMOSA 79 (3): 81-94.

In 2005, Whooper Swan was recorded as a new breeding bird species in the Netherlands. The breeding pair was found in a small lake in a lowland peatland area (Wapserveense Petgaten) in the province of Drenthe, in the eastern part of the country (52°50'N, 6°12'E; Fig. 1). A copulating pair of Whooper Swans was observed in the area on 12 April 2005 but was given no special attention. However, an incubating female was seen from mid-April onwards. The clutch contained six eggs, of which at least four hatched on 23 May. After 21 days all four cygnets had disappeared (unknown cause). Incubation must have started between 12 and 18 April. With the exception of the period from 15 August -15 October 2005, when the swans presumably moulted their flight-feathers elsewhere, the breeding pair remained in the area and were observed regularly.
On 9 April 2006, the same pair (recognised by colour pattern on the bill) was found around the old nest. On 20 April, three eggs could be seen in the nest; on 4 May two cygnets hatched. This time incubation had started around 1 April. First observations of flight activity were made when the cygnets were 88 days old (30 July). At 120 days they were able to take off for a distance of a few 100 m. By the same time, the female had started wing moult.
Only the female incubated the eggs. Most of the time the male stayed close to the nest, guarding the female. He was always very vigilant and slept only occasionally (Tab. 1). Both male and female made almost daily feeding trips to a nearby marshland area (Polder Ten Kate; 61% of observed feeding time), that is dominated by Water Horsetail Equisetum fluviatile, or to an agricultural area, where they fed on Ryegrass Lolium perenne (24%). The male made more frequent and more prolonged feeding trips than the female (average duration 72 and 42 minutes, respectively). In 2005, the cygnets remained at the nest site and commuted to the neighbouring Polder Ten Kate for feeding. In 2006, the brood almost directly moved to this polder and did not return to the nest site at all. By the end of July, they moved to a nearby sand pit, presumably because the polder started to dry out. After two weeks, the swans moved again, to another sandpit at some 5 km distance, after food resources at the first sand pit had presumably been depleted. During chick-rearing, both parents spend approximately half of the time feeding (Tab. 1). The male spend more time vigilant than the female. Feeding time did not change over time, whereas birds were less often vigilant and spend more time swimming and preening later in the season. Six times antagonistic behaviour was observed. Mute Swans Cygnus olor were successfully chased away from nesting and feeding areas. Once, an unknown mammalian predator was attacked and successfully chased off.
The main food resource for both adults and cygnets at the nesting site was Stonewort Nitella flexilis. In Polder Ten Kate the family of swans predominantly fed on younger stems and leaves of Water Horsetail and also frequently younger stems and leaves of Canary Grass Phalaris arundinacea and the buttercup Ranunculus sceleratus. In the sand pits, the swans fed on rhizomes of Fennel Pondweed Potamogeton pectinatus and leaves of Common Reed Phragmitis vulgaris. Breeding of Whooper Swans in The Netherlands is in line with the recent breeding range expansion of the increasing Northwest- European population. In 1965-2005, the species colonised the Baltic States, Poland, United Kingdom, Ireland, Germany (1994), Denmark (2002) and Hungary (2005).

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