Given a reasonable view, the differences between whooper bird and the superficially similar Bewick's Swan are obvious. The Whooper is a bigger bird, some 25-30 percent heavier, with a longer straight neck and a flattened forehead that gives its head a distinctive profile. These features are useful for distinguishing the birds both flying and at rest. However, the diagnostic feature is the bill pattern, with a longer, deeper bill showing more yellow than Bewick's, a large wedge of yellow on the bill sides extending to a point towards the bill tip. The juveniles tend to be browner than Bewick's juveniles, with a similarly coloured bill of pinkish and black. Juveniles gradually acquire the white plumage of adulthood at 15-20 months old.
Whooper bird is more widely distributed than Bewick's Swan, avouring a more sub-Arctic breeding enviroment, although there is a good population in iceland.It nests on a variety of wetlads, favouring undistributed reed-fringed lakes, swamps and pools in moorlands and in low-lying steppe and grasslands areas. A very rare occasional breeder in Britain, it is most regularly encountered in the north and west, though in winter whooper bird occurs more widely and can be found on lakes and flooded pastures (such as the large wintering population found on the Ouse Washes in Cambridgeshire) and often along the coast. It requires aquatic vegetation on which it feed, but can often be seen grazing in arable fields.
Whooper bird is similar in general to the vocalizations of Bewick's Swan, but Whooper birds typically sound stronger, deeper and more trumpeting. The flight call is a double bugle or toy trumpet-like "ahng ahng", "barp barp baah-hpl", "raaahng haaangh" or "whoop-whoop", repeated several times and with the second syllable slightly higher in pitch. A flock in flight sounds louder than Bewick's, while at rest the varied calls produce a chorus of harmonious babbling..