In Europe two species of shelduck are found, the Common Shelduck Tadorna tadorna, and the Ruddy Shelduck T. ferruginea. Common Shelducks are mostly coastal birds, whereas Ruddy Shelducks tend to frequent saline lakes inland, and have a range extending further east into Central Asia and India. There are some records of Ruddy Shelduck from previous glacial and interglacial periods in the UK, and they also turn up as vagrants from Eastern Europe, causing much anguish amongst birders as they try to decide if they are genuine vagrants or escapes (various shelduck species are common in waterfowl collections).
At present, Bristol has 3 shelducks in the collection. However, they may confuse people as to their correct identification, as they are hybrids of Ruddy and Common Shelducks. Originally we had both the parent species, and eggs from a female Ruddy Shelduck were raised believing they were purebred birds, as the ducklings of Ruddy and Common Shelduck are extremely similar. As they matured it became plain that they were a mixture, so they are just display birds now and are not bred from. Oddly, they seem in many ways to resemble the Cape Shelduck T. cana of South Africa. For hybrids to resemble a completely different species to either of the parents is not uncommon in waterfowl, which as a group are prone to hybridise in both captivity and the wild.
(images from wikipedia)