Pekin duck is laying eggs with soft shells?

[Wifezilla]

I feed game bird food and just have a separate tub for the crushed egg shells. My drake never touches the shells.

 

[TheDuckCrew]

well i have three drakes and one hen (working on getting more girls, i know its not good.) the boys have all been kept apart because of fighting, so the pan of egg shells will go where she goes!

 

[sonny dee]

Noticed if my drakes get oyster shells, they start limping, due to too much calcium. To solve, I add yeast to their food. Just a few sprinkles.