Duck shakes with excitement....? (Vibrating ducks)

[Daphne_loves_mealworms]

I don't mean to bump this up again, but Im very interested! Does anyone have a hen that does this? My suspected female duck does this when she gets extremely excited, and I doubt it could be mating behaviour as she's not mature yet-- and quacks, so I'm fairly certain she is a gril! Just curious!

I have a Muscovy hen that does this, and had a Rouen hen that did it as well. The Muscovy hen that vibrates is the more dominant of my Muscovies, and my Rouen hen was kind of masculine (but definitely a hen). I don’t know if dominance plays a role at all?