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:
They are very site-faithful and it is common for them to return to the same wintering site year after year.
The whooper swan is similar in appearance to the Bewick's swan. However, it is larger in size with a length of 140-160 cm (55-63 in), a wingspan of 205-235 cm (81-93 in) and a weight range of 8-15 kg (17.6-33 lbs). It has a more angular head shape and has more yellow than black on the bill (Bewick's swans having more black than yellow), but the bill pattern is less variable than for Bewick's swans.
The swans traditionally wintered on lakes, estuaries, marshes and floodplains, where they fed on aquatic vegetation, but use of agricultural land has become far more frequent since the 1960s. Waterbodies remain important as roost sites, but the swans now feed mainly on farmland (on pasture, cereal stubble and root crops) during the winter months. Lives on wetland habitats in the breeding season, mainly on lakes, marshes and coastal bays, at altitudes ranging from sea level at coastal sites to 700m in the Icelandic highlands.
Birds mostly move south from their breeding grounds in October-November, often stopping off at freshwater lakes, shallow bays or rivers, returning northwards in March-April. Whoopers from western Iceland winter mainly in Ireland and west Scotland whereas those from eastern Iceland are more likely to winter in the rest of Scotland and in continental Europe. There is also a tendency for the swans' distribution in Britain and Ireland to shift southwards as the winter progresses. The 800 km flight from Iceland to Scotland, and 1,300 km flight direct from Iceland to Ireland, is probably the longest overseas flight undertaken by any swan species. There are therefore no staging sites separate from the breeding and wintering ranges, but sites in northern Britain and Ireland act as major landfalls in autumn, with sites in southern Iceland similarly being important for whooper swans in spring.
Whooper swans are typically monogamous and most pair for life, though "divorce" does occur with 5.8% of paired swans re-pairing whilst the original mate is still alive. Pair formation may occur in winter flocks, but more frequently in non-breeding herds in spring and summer. The pairs are highly territorial when nesting and generally remain on their territories until the young have fledged, although some pairs with young may join non-breeders on lakes to moult. Both the male and female help build the nest, and the male will stand guard over the nest while the female incubates. The female will usually lay four-seven eggs, and the cygnets hatch after about 31 days of the clutch being completed. The cygnets fledge at around 90 days, in time for migration in October. They accompany their parents on autumn migration and stay with them during their first winter, but unlike Bewick's swans it's very unusual for whoopers to be seen with their parents in their second winter.
Whooper swans are highly vocal, with sonorous bugling calls. These are used during aggressive encounters, with softer "contact" noises used as communication between paired birds and families. Calls accompanying pre-flight head-bobbing are also important for maintaining pair and family cohesion. Several types of threat display are seen in winter to establish the dominance hierarchy in the wintering flock, ranging from head-low threats and pecks to more dramatic neck-stretching and wing-flapping displays, resulting occasionally in physical combat. Courtship consists of mutual head-turning and wing-flicking, with the pair facing each other.
The whooper swan has a widespread breeding distribution, extending from Iceland and northern Scandinavia, across Russia, to the Pacific coast. Those nesting in continental Eurasia occur primarily in subarctic regions in the taiga zone, south of the Bewick's swans' high arctic breeding range. Counts and ringing programmes have confirmed that most swans from the Icelandic-breeding population winter in Britain and Ireland, but up to 1,500 over-winter in Iceland, and there is some low-level interchange with the mainland European population. Continental whoopers also migrate to winter in northwestern Europe, the Black Sea region, the Caspian Sea region and eastern Asia. Whooper swans are rare breeders in northern Scotland, with only a handful of pairs breeding there in recent years. This bird is an occasional vagrant to western north America.
The tracking of whooper swans will enable WWT to learn more about the swans' migration route, the areas where they stop off to feed and rest and key information about the height and speed at which they fly. This information will help to protect their flyways and thus safeguard their future.
There are a number of factors that can threaten the survival of whooper swans both during their migration and at their breeding / wintering sites. Collision with power lines is one of the most common causes of death. Poisoning through ingestion of spent lead shot continues to be a significant issue for the swans, because it persists in the environment where it is ingested by the birds. Illegal shooting also occurs; of the whooper swans caught and X-rayed at WWT centres in recent years, 10-12% were found to have shotgun pellets in their body tissues.
Offshore and onshore wind farms, if located on the whooper swans' flyway, potentially could be harmful as the swans may be at risk of flying into the wind turbines.
Land use change can adversely affect the availability of feeding and roost sites on the wintering grounds.
Drainage of wetland breeding sites, or large scale habitat loss through hydropower schemes, may reduce the swans' breeding range.
