How old do roos need to be before they can . . .ummm, get the job done? We (me & my son) built a homemade incubator for a science project, but need fertile eggs. Wondering when that "bulls eye" in the yolk will appear, lol - might just have to purchase some. I'm in Sibley and don't know of anyone keeping chickens around me. Anyone in NW LA selling fertile eggs?