it's NOT a guinea egg. guineas lay very pointed eggs but yes they will lay in the nesting boxes.
if it's small, it could be one of your young ones with a first egg. first eggs are usually small.
LOL, ok, I do have a single guinea egg, new guinea hen was crated with nothing but another guinea and produced a single egg. I'm pretty sure that one is most definately a guinea egg. I'll take pictures of the two together later today. That should help solve that particular question.
Well I never got to comparing the two eggs but today the guinea was in with the goats and I got two more eggs. Even if my ameraucana was laying pink/brown eggs (which I don't think she is), I seriously doubt she's laying two eggs in a day. I think I have a couple of early layers. Maybe that's a question for the BA crowd, are they known for being early layers?