The shelducks are a group of larger, often semi-terrestrial waterfowl, which can be seen as intermediate between geese and ducks. Some are so large that they are called geese. The Common Shelduck (Tadorna tadorna) is the most familiar gooselike duck, boldly patterned in black, white and chestnut, the male carrying a conspicuous knob on his bright red bill in spring.
The Common shelduck feeds mainly on the tiny snails that swarm on mudflats in river estuaries. It also feeds on other invertebrates, including worms, shellfish, crabs, shrimps, sandhoppers and larvae of flies. Small fish and plant material are also eaten. They swim high in the water and up-ends to reach submerged food. It also wades, sweeping its bill from side to side to sift food out of the mud. In-flight, it looks heavy, with slow wingbeats. Like several other duck species, it nests in burrows or tree hollows, leading its young to water as soon as they are able to make the journey.
Common shelducks are quite vocal, especially just before and after breeding season. They utter a variety of whistling notes, most often being soft, clear whee-chew, becoming urgent and frequent if danger threatens. Ducklings utter high-pitched peeps, when moving and feeding, and soft trills when in close contact.
Common shelducks are widespread around coasts of north-west Europe, in the northern Mediterranean, and from the Black Sea east through Central Asia to Mongolia and western and northern China. These birds do not migrate to breed, but after breeding, most of the population of northwestern Europe migrate to Waddenzee of the Netherlands. Here, they are relatively safe from predators, which is important, because at this time of the year, they molt and replace all of their flight feathers. During molt adults look whiter and less well-marked.