I need some help with this. My duck is about 1 year or more and has been laying on a regular schedule the whole 4 months I have had her. Yesterday she layed a normal thick shelled egg then later a softer shell and then a no shell egg this morning. My question is: do I need more calcium for her? I keep oyster shell in a hanging feeder in the pen and add more when needed but I don't know if she uses it or if its just the chickens that do.