The Trumpeter Swan (Cygnus buccinator) at Slimbridge.
It is the heaviest, tallest, loudest of all wildfowl species on earth. It is the North American counterpart and a close relative of the Whooper Swan of Eurasia. The adult Trumpeter Swan is all white in plumage. As with a Whooper Swan, this species has upright posture and a straight neck at all times (as in the second fig). The Trumpeter Swan has a large, wedge-shaped black bill that can, in some cases, be minimally lined with salmon-red coloration around the mouth (main image). Its black bill is useful in distinguishing the Trumpeter Swan from other species of wildfowl.