Call duck eggs-how will I know?

[DoubletakeFarm]

Stupid question here: When my call ducks start laying will I be able to tell their eggs from my bantam chicken eggs? I will be gathering the call duck eggs for incubation and eating the chicken eggs, and I'm worried I won't be able to tell and will eat my ducks by accident, lol!

So those of you that have calls and bantam chickens..is it easy to tell which is which?

Gratuitously cute pic of a one day old call with a two day old silkie:

 

[Ameraucanas]

The first pic is a chicken egg, the second is a call egg.
Your ducks will start laying around 20-24 weeks.

 

[DoubletakeFarm]

I don't see a first pic. My ducks hatched 4-22-15 which would make them 27 weeks old. They don't lay this late in the year do they? They are definitely breeding but I figure I won't see eggs until spring.