Whooper Swan Cygnus cygnus is essentially a trans-Palearctic species breeding disjunctly across an enormous range of the forested boreal zone of Eurasia, from Iceland, Norway, Sweden and Finland, across northern Russia to Okhotsk Sea and Sakhalin, the Bering Sea and Kamchatka, and even on the outer Aleutians (USA). The species breeds mainly in the taiga zone, but are locally extending north into forested tundra and true tundra, and south where there is suitable habitat into steppe i.e. to the Caspian Sea, Mongolia and northern China. The Whooper Swan is predominantly migratory and ranges south across western Europe, to Ireland, Britain, Netherlands, Denmark, Germany and Poland, and mainly in cold winters further south. It also winters on the Black and Caspian seas, coastal eastern China, the Korean Peninsula, Japan and Kamchatka. Whooper Swans wintering in Ireland and Britain are predominantly Icelandic migrant populations.
The Whooper Swan numbers among the most abundant swans, with current global estimates likely to be between 150,000 and 200,000. The Icelandic Whooper Swan populations in particular were recorded to be 26,366 after a coordinated count in January 2005. Most Whoopers Swans from the Icelandic population spend the winter in Britain and Ireland. Of this Icelandic population, a wintering population of 9,748 were estimated to occur within Ireland in January 2005. More recent population estimates are currently not available. Whooper Swan migrant populations from Iceland are monitored through the Irish Wetland Bird Survey (I-WeBS), with a swan census carried out every five years. These migratory populations have been monitored in Ireland since the 1950′s. The aim of these censuses is to monitor population numbers of Whooper Swans, and also to assess breeding success and habitat preference changes.
Whooper Swans are listed under Annex I of the EU Birds Directive (EU 79/409/EEC). Whooper Swans are further protected as they are listed under Annex II of the Berne Convention on the conservation of wildlife and natural habitats. The European populations have been classed as Secure from an assessment by BirdLife International. In Ireland they are also amber listed in ‘Birds of Conservation Concern in Ireland’ due to more than 20% of the European wintering population occurring here. This listing is also because the majority of Whooper Swans winter at ten or less sites, in addition to its very small breeding population.
Whooper Swans form solitary pairs when breeding at their trans-Palearctic breeding grounds in mid-May-August with well defined territories with non-breeders remaining in flocks separate from breeding pairs (Snow and Perrins, 1998). The species begin to migrate once they have undergone a post-breeding moult that occurs between late-July and early-August. The species migrates south from their trans-Palearctic breeding grounds during late-September to October, although the exact timing is dependent on weather conditions. During this period Whooper Swans migrate from Iceland and remain in Ireland until March to April or early-May before departing for the breeding grounds once more. Some travel directly to their chosen wintering sites in Ireland, while others transit Scotland en route. Whoopers are highly sociable outside of the breeding season, migrating in small to medium sized flocks comprising of many family groups. The swans are usually seen to congregate in flocks of up to 300-400 individuals during their wintering period. Studies have shown a high degree of site-fidelity in this species for both breeding and wintering sites.
Upon migration to Ireland from their breeding grounds in Iceland the species is known to frequent lakes, estuaries, sheltered coasts and agricultural land. Freshwater lakes and marshes, floodlands, brackish lagoons, reservoirs, coastal bays and inlets, and even small pools and rivers are traditional wintering grounds for Whoopers Swans. In Ireland, turloughs can host internationally significant numbers of visiting Whooper Swans due to their shallow nature and the full vegetation cover of the basin.
Whooper Swans require a laboured effort when taking off from either water or land due to their size and short legs. The need for a clear run-way for take-off limits places where they able to land. Once airborne the Whooper flies powerfully with regular wing beats that can be sustained over very long distances. The Whooper Swan is one of the highest flying of all birds, being recorded at heights above 8000m over the British Isles during their migratory flights. Although in general, Whoopers migrate at very low altitudes with high-flying swans at altitudes of 500-1856m. They are not agile in the air and appear sluggish, turning in wide arcs, climbing slowly, and even descending far less rapidly than other large bird species such as geese. Whooper Swan is predominantly a herbivorous species, its diet comprises mainly the leaves, stems and roots of aquatic vegetation. However, they are increasingly being recorded grazing on grass in pasture and spilt agricultural grain, as well as vegetables (e.g. potatoes and turnips) from cultivated land and acorns (Chisholm and Spray, 2002). In Ireland, it has been found that a pronounced seasonal shift in habitat / food preferences from October to April. Whooper Swans were initially observed to be foraging at aquatic sites, shifting to stubble / potatoes, to winter cereals, to grasslands, then back to winter cereals. Worden et al. 2009 observed that while Whooper Swans were recorded most commonly on pasture in Ireland, the use of arable land had increased from 7% to 27% during the last three international censuses conducted on the species over a 15 year period. Whooper Swans foraging on land some distance from water make regular daily movements between roosting and foraging areas. The swans usually use daylight hours for feeding and leave these sites at dusk to congregate at evening roosts. Whooper Swans are known to regularly fly up to 30km from their roosts in order to reach attractive foraging grounds.
Habitat degradation and loss including the reclamation of coastal and inland wetlands is a major global threat to Whooper Swans. Agricultural expansion, wetland drainage for irrigation, overgrazing by livestock (e.g. sheep), vegetation cutting for winter livestock feed, the development of roads, hydroelectric dam construction, and disturbance from tourism are threats to the habitats used by this species across its range. Heavy population losses may be suffered by Whooper Swans from flying accidents (including collisions with overhead lines), poisoning from lead shot or fishing weight ingestion, natural disasters such as droughts or heavy snowstorms, and may be threatened by future outbreaks of disease as the species is susceptible to avian influenza. Although Whooper Swans have long been protected from hunting throughout their migratory ranges (since 1885 in Iceland, 1954 in the UK, 1964 in Russia and 1976 in Ireland) there is still thought to be illegal hunting of this species in Britain, Ireland and Iceland. Collisions are a significant cause of mortality in swans, where they are particularly susceptible to collisions with wires.
The increasing numbers of wind farms in many parts of the Whooper’s west European wintering range, including Ireland, pose a more recent threat to those moving between feeding and roosting areas. This threat is not just from direct collisions with turbine rotors but also from the associated installations i.e. powerlines that transfer produced energy away from a site. A report by BirdLife International highlights that there is a risk of both disturbance by and collisions with wind turbines for Whooper Swans (Cygnus cygnus) (BirdLife International, 2003). There is also the potential for barrier effects to occur, where bird species have been observed to alter their migration route to avoid wind turbines. This could increase the distance birds are required to travel between roosting and foraging grounds thereby resulting in greater energy expenditure that may potentially impact upon individual survival. However, no published scientific literature suggests that barrier affects have significant impacts on populations.
To maintain the required nutritional intake, Whooper Swans are encouraged to spend as much of the day as possible in foraging. Whooper Swans make regular daily movements between roosting and foraging areas. They have been observed to regularly fly up to 30km from their roosts in order to reach attractive foraging grounds. The Whooper swan is not particularly manoeuvrable (as with other swans and geese) in flight, turning in wide arcs, due to their high wing loading. These birds only have a narrow zone of binocular vision to the front and rear, making them rather poor at detecting thin horizontal objects ahead of them. Whooper Swans are prone to collisions with thin horizontal objects ahead of them such as telephone and power lines, trees and wind turbines during their typical low-altitude flights between roosting and foraging sites. Swans have been stated to have a high hit-wire index, although the data used to make this conclusion has not been published in a scientific peer reviewed report. Flights between foraging and roosting grounds are often at low-altitude in low light levels, i.e. pre-dawn and post-dusk periods, and therefore in poor visibility. Monitoring of Whooper Swan daily movement patterns has shown that flocks typically fly at 5-30m above the ground. This potentially brings birds within the height of the rotor area for medium and large turbines. Poor flying conditions, including strong winds and poor light conditions that could affect a birds manoeuvrability during flight could greatly increase the collision risk. Birds could potentially be attracted to the lighting of wind turbines, particularly during bad weather conditions that may also potentially increase the risk of collision. Bird collision risk and mortality assessment, arising from collision or electrocution, should include wind turbines and the associated structures such as overhead power lines (if planning on being erected) that would transport energy from the wind farm.
While current studies investigating collisions caused by wind turbines indicate relatively low levels of mortality, care needs to be taken as to the reliability of these results in helping form decisions regarding planning permission. Many of these studies were carried out on wind farms located away from large bird concentrations. Their results also relied on finding corpses, but did not take into consideration for corpses that were overlooked or removed by scavengers. Negative effects on Whooper Swans from wind turbines could occur up to 600m away. Disturbance may be caused by the turbines themselves through visual, noise, and vibration impacts, or as a result of vehicle / vessel and personnel movements related to site maintenance. However, detailed scientific studies are currently lacking to support the theory of disturbance from turbines and require more research. Evidence suggests that habituation to wind turbines is unlikely and that impacts are likely to persist or worsen with time leading to reduced bird abundance, at least in some cases.
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