Mute Swan

The UK's largest water bird, the mute swan (Cygus olor) is a common sight on waterways and in parks across the country. Their long, s-shaped neck allows them to reach submerged food, including aquatic plants, insects and molluscs. The large wingspan of the mute swan (between 208 and 238cm) allows them to get airborne despite weighing 10-12kg. Other identifying features include an orange bill with a black base and knob. Both sexes have this black basal knob, but the male's swells in the breeding season, perhaps as an indicator of sexual maturity or good health. Outside of the breeding season, the sexes are difficult to distinguish, although males are often slightly larger. 


A pair of mute swans showing off their bright orange bills. The brownish colour
of their heads may be due to staining from slightly acidic waters.

Mute swans are often seen as a romantic symbol because of the way their long necks form a heart shape during their mating rituals, and fittingly, they often mate for life, though some will have multiple partners. Pair bonding can begin when swans are 2 years old, and they are typically sexually mature by 3. As well as having the same partner each year mute swans generally use the same nest year on year. Nests are made of a mound of vegetation where the female will lay one egg every other day, up to a total of 5-12 eggs. She lines the nest with feathers plucked from her underside - the brood patch. Plucking these feathers provides warmth for the eggs in two ways; the feathers in the nest add insulation, and the bare patch on the mother's underside allows the eggs to be closer to her warmth. The eggs are incubated by the female for 5-6 weeks then all hatch within a 24 hour period. Although the male doesn't incubate the eggs, he will guard the nest while the female is away to feed. The cygnets enter the water the day after hatching, spending a fair amount of time on their mother's back. When they first hatch, the cygnets are grey, gradually changing to brown then white as they mature. 


A mute swan nest on the river Yare


A juvenile mute swan - it's feathers are grey and it's beak is
not yet the bright yellow like the adults.

There are believed to be around 6400 breeding pairs of Cygnus olor in the UK, with a total of 74,000 individuals overwintering here, as some arrive from Europe. This number has increased since the 1980s, primarily due to legislation prohibiting the use of lead weights in angling. In the past, poising by lead was a large threat to swan populations - it killed an estimated 4000 birds annually in the 1970s and 80s. Anglers would discard weights made of lead, a toxic metal, which were then consumed by swans when they were feeding or seeking grit for the gizzard. Legislation outlawing the import, sale, and use of certain sizes of lead weight was brought in in 1987, after which the percentage of C. olor deaths caused by lead poisoning fell from 34% to 6%. Currently, mute swans are protected under the Wildlife and Countryside Act 1981, but they still face threats including entanglement in fishing tackle and collision with suspended power lines. Their current UK conservation status is amber. 


A mute swan on the River Yare, UEA


https://www.rspb.org.uk/birds-and-wildlife/wildlife-guides/bird-a-z/mute-swan/
https://www.wildlifetrusts.org/wildlife-explorer/birds/waterfowl/mute-swan
https://scottishwildlifetrust.org.uk/2020/04/mute-swans/
Regulation of lead fishing weights results in mute swan population recovery

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