Adults of this large swan range from 170 cm long with a 240 cm wingspan. They may stand over 120 cm tall on land. Males are larger than females and have a larger knob on their bill.
The Mute Swan is one of the heaviest flying birds, with males (known as cobs) averaging about 12 kg and the slightly smaller females (known as pens) weighing about 9 kg. Its size, orange-reddish bill and white plumage make this swan almost unmistakable at close quarters. Compared to the other Northern white swans, the Mute Swan can easily be distinguished by its curved neck and orange, black-knobbed bill. Unlike most other Northern swan species (who usually inhabit only pristine wetlands without regular human interference), the Mute Swan has, in some parts of the world, become habituated and nearly fearless towards humans. Such swans are often seen at close range in urban areas with bodies of water.
Young birds, called cygnets, are not the bright white of mature adults, and their bill is dull grayish-black, not orange, for the first year. The down may range from pure white to grey to buff, with grey/buff the most common. The white cygnets have a leucistic gene. All Mute Swans are white at maturity, though the feathers (particularly on the head and neck) are often stained orange-brown by iron and tannins in the water.">