Chicken or egg

Dr Livingstone found an egg in the front garden. I had seen it two days earlier but thought it was a snatched and empty egg. Sometimes the pine marten robs them from the coop. But Dr Livingstone brought it to the kitchen and said:'It's still in tact, I'm having that for breakfast!'. I took another egg we got from our neighbour, its different.
I'm guessing that egg belongs to a duck rather than a chicken.
He boiled them together, luckily it turned out the duck egg wasn't fertilized.