Ruderente St. Gallen

The ruddy duck is a small, stocky diving duck measuring around 35 to 43 centimetres in length and weighing 500 to 600 grams. It is easily told by its long, often vertically cocked stiff tail and the broad, in breeding plumage strikingly blue bill of the drake. Breeding males show a black crown, white cheeks and a deep rufous body. Females are plain greyish-brown with a dark cheek stripe. The legs are set far back on the body, making the species an excellent diver but clumsy on land. The main risk of confusion is with the closely related white-headed duck (Oxyura leucocephala), which is larger and in the drake has an entirely white head and a heavily swollen-based, likewise blue bill.

The natural range of the ruddy duck lies in North America, from Canada to the southern United States. It reached Europe in the 20th century through private and zoological waterfowl collections in Great Britain. Birds escaping from these collections established a free-flying breeding population in Britain from the middle of the 20th century onwards and spread from there across the Channel to the European continent. Records and breeding events have since been reported from many countries of the Western Palearctic, among them France, the Netherlands, Belgium, Germany, Spain, Morocco, Ireland and Iceland. In Germany the species occurs as a rare visitor with sporadic breeding records and is regarded as an established neozoan.

The ecological threat posed by the ruddy duck lies less in its absolute numbers than in its close relationship with the European white-headed duck. The white-headed duck is globally endangered and has its stronghold in the western Mediterranean, in particular in Spain. Ruddy ducks pair successfully with white-headed ducks and produce fertile hybrids. This genetic introgression is considered one of the greatest threats to the continued existence of the white-headed duck as a distinct species. Competition for food and for the few suitable breeding waters adds to the pressure. For this reason the EU has placed the ruddy duck on the list of invasive alien species of Union concern (EU Regulation 1143/2014, the so-called Union list). Member states are accordingly obliged to prevent further range expansion and hybridisation.

In practice, coordinated control and removal programmes have been running for years. Great Britain has reduced its original source population to a minimum through a state-funded eradication programme. Spain, Portugal and France remove ruddy ducks and hybrids in a targeted manner from the waters where white-headed ducks still breed. In Germany too, individuals encountered in the wild are removed within the framework of nature conservation and hunting law. For hunters the key consequence is identification: the ruddy duck must be safely and unambiguously distinguished from the similarly coloured but protected pochard and tufted duck, and above all from the white-headed duck. Removal is permitted only within officially mandated management measures or in line with the relevant federal-state and conservation rules on combating invasive alien species.