Although becoming quite rare in southeast Europe and southern Spain, the ruddy shelduck is still common across much of its Asian range. It may be this population which gives rise to vagrants as far west as Iceland, Great Britain and Ireland. However, since the European population is declining, it is likely that most occurrences in western Europe in recent decades are escapes or feral birds. Although this bird is observed in the wild from time to time in eastern North America, no evidence has been found that this is a genuine case of vagrancy. Feral ruddy shelduck have bred successfully in several European countries. In Switzerland the ruddy shelduck is considered an invasive species that threatens to displace native birds. Despite actions taken to reduce numbers, the population of ruddy shelduck in Switzerland increased from 211 to 1250 individuals in the period from 2006 to 2016.