A few comments on the Mute Swan questions:
-there’s a large wintering population of Mutes in NE Greece (e.g. up to several thousand on Evros delta) so to that extent they are not sedentary in SE Europe
-not sure where those birds come from, but presumably Ukraine, Danube delta etc. and around northern Black Sea
-they don’t have a regular dispersal from NE Greece, but in v cold snaps seem to head SW into Balkans and beyond, e.g. southern Italy where there have been previous cold weather influxes (remember the three that got as far as Malta then were shot a few years ago)
-a potentially significant difference to my mind between Whoopers and Mutes is that the Mutes tend to roost and feed in same place, up-end in deep water, whereas Whoopers in SE Europe and ?elsewhere tend roost on water, flight out to feed on cereal fields (for example, I’ve seen small numbers of Whoopers roosting with Mutes on Evros and then flighting inland at dawn whilst the Mutes stay put)
-similarly, the geese in Bulgaria tend to feed on autumn-drilled cereal where they can (i.e. with any spread manure etc. ploughed in some months before they arrive)
As a separate point, die-off of 135 “wild swans” reported on Iranian Caspian shore this week in the FT.