Whooper Swans are amongst the heaviest of migratory birds weighing around 10 kilos (adult males). Most Icelandic breeding Whooper Swans winter in Britain and Ireland and can be seen at WWT centres: Castle Espie, Caerlaverock, Welney, Martin Mere and Slimbridge. They are very site-faithful and it is common for them to return to the same wintering site year after year.
They breed in a broad band of sub-arctic and taiga habitats across northern Eurasia, from Iceland and northern Scandinavia in the west to Mongolia, northern China and the Russian Far East.
Key sites for Whooper swans include Lough Neagh, Lough & River Foyle, Lough Swilly, Ouse Washes (Welney), Martin Mere / Ribble Estuary, Upper Lough Erne, Lough Beg
Up to 7000-8000 swans have been counted at Lonsfjordur, on the southeast coast of Iceland. These include families in spring and autumn, with some 5000 non-breeders moulting there in August. The swans are also widespread in Iceland, except for the central glacial regions.
Diet
Whooper swans are almost totally vegetarian, although breeding pairs in Iceland take emerging Chironomids in spring and other invertebrates may occasionally be ingested.
Horse-tails and sedges seem to be the preferred food on the breeding grounds.
Winter diet traditionally included eelgrass, wigeon grass, pondweeds, stoneworts, horsetails, sweet-grass and roots of marsh yellow-cress. Increasing numbers were seen on farmland in the second half of the 20th century, on cereal stubbles, winter cereals, sugar beet and potatoes left after harvesting, and oil-seed rape. Nevertheless, Whooper Swans still feed mostly on improved pasture in winter.
Family Life
Pairs are highly territorial when nesting and generally remain on territories until the young have fledged. Clutch sizes of up to 7 eggs have been recorded, though usually there are 3 - 5 eggs in the clutch. Similarly, parents are seen with 1 - 7 cygnets on the wintering grounds. The young remain with their parents only for the first winter, sometimes separating from them before heading back to Iceland in the spring.
Whooper Swans are generally monogamous but divorce does occur; 5.8% of paired swans re-pair whilst their original mate is still alive. Pair formation can occur in winter flocks, or more frequently in non-breeding herds in spring and summer
First breeding has occurred in second summer in Iceland (ie at 1 year old, with DNA finger-printing confirming parentage), but first pairing is more usually at 2-4 years with first breeding at 4-6 years. Non-breeding birds are gregarious, occurring either in small groups or larger flocks.