If all of this Ruddy Duck discussion was not so depressing, Daniel Kratzer has informed me of 400 Ruddy Shelducks eradicated in Switzerland - see link here http://www.ag.ch/umwelt-aargau/pdf/UAG_38_29.pdf
It has always been believed that a mixture of both wild and non-naturalised Ruddy Shelducks make up this population that move between Germany and Switzerland - Lee Evans