Above is a photograph of an eider. It is a species of duck. Why did the Danes want to give Denmark to a duck?
It could be that King Frederick VII of Denmark had only became king in January 20, 1848 and so he was new to the job and perhaps his inexperience showed.
Maybe King Frederick VII looked goofy in the royal regalia and fidgeted with the scepter? (I assume the monarchy has a scepter)
Could it be that the Danish nationalist thought the King Eider wasn't just a type of duck but the rightful monarch? I would guess that Duck legitimism (like Carlists in Spain, Jacobists in the UK or French legitimists like Orleanists or Bonapartists) might be called Quackists?
Or maybe the Danish really just have a thing for ducks? After all, ducks can walk, swim and fly – a triple threat. That's probably it.