Apart from the Goose and Shelduck, do you exclude any other species from your list? Ring-necked Parakeet perhaps?
I thought the Ruddy Shelduck influx a few years back coincided with a genuine influx of wild birds into Holland and so those records at least should have been tickable.
CB
Not sure why anybody should regard Egyptian Geese as just escapes. The WeBS count for the UK was 724 in 2010/11, there is an increasing and self-sustaining population - many are in East Anglia but to quote "strong evidence of the steady expansion taking place away from the East Anglia core. The above average monthly index value for September infers high breeding success of the increasing population, presumably aiding the range expansion". On top of this is the large population in Holland of 35,000 - kept in check by much shooting - surely some of these birds also make their way to the UK. So strong evidence that the increasing number of Egyptian Geese we are seeing in C&W are from the increasing feral population.
Ruddy Shelducks are a bit more problematic. As for the influx mentioned above - this was in 1994. It does seem highly likely that there was an influx of wild birds west across Europe that year, and probable that some of these birds made their way to the UK, maybe even to Cheshire where 12 were counted in one day with many other records. However, BOU were not convinced that they were not just birds from the NW Europe feral population. So if they were not wild they were feral - i.e. from a self-sustaining population. Currently the size of this feral population is disputed, but appears not to be particularly big. But there is a regular moulting flock on the Wadenzee every summer several hundred strong, as well as larger numbers moulting in Switzerland - so these birds must be breeding somewhere in Europe. Apart from the occasional influx it does seem that numbers in the UK are small and that the population in this country is not self-sustaining. On the other hand their regular appearance, especially with the late summer peak, seems to indicate a non-escape origin for at least some. Certainly David Cabot in 'Wildfowl - New Naturalist' is of the opinion that 'these feral populations
(in NW Europe) together with escapes from wildfowl collections, are almost certainly the source of all birds seen in Britain and Ireland today'. So IMO there is at least a good chance that any Ruddy Shelducks seen in C&W originate from the NW Europe feral population. Wild birds are possible but would be very rare vagrants and impossible to prove without ringing, or capture and isotope analysis.
. Estuaries are a whole different ball game tho
