well drake, actually.
He's a Muscovy, 4/5 years old, living with my little flock (6 ducks and 2 drakes altogether, not all Muscovives). Free range, but shut in an old stable at night.
For the past 3 or 4 weeks he's been getting increasingly unsteady on his feet, he can walk - slowly - on level ground, but any uneveness, or going up a step or over a door threshold he falls over and has to scramble up using his wings to help. He potters about on his own during the day (because he can't keep up with the others) and comes in with the others at night, and is eating normally. His feathers are a muddy mess now, I don't think it's wet feather as such, I think it's just that he lacks the strength in his legs to be able to preen properly.
I've examined him and there are no visible wounds, swellings, or heat in his legs or feet. All the other ducks are fine.
Anyone experienced similar, or have any ideas what it could be? I've been googling for an hour and can't find a description of any disease that comes close.