Name That Egg

Friends of mine called this evening to say that they had found a huge egg under the mulch in the landscaping in front of their house. It appeared to be buried there. They called the KOOK and asked if I might have an idea what kind of egg it could be. I couldn't resist taking a ride over there to get this shot. My first thought was a goose egg - but this is a fairly active neighborhood and no geese have been seen there. I checked the internet and looked at pics of snake and turtle eggs - however, the shell is hard. The next thought was turkey, but the sources say that turkey eggs are only around 3" and this is 4". After taking a few pictures of it, they recovered it with the mulch and hopefully a predator will not find it.

Any guesses? Please leave a comment if you have any ideas. It's definitely a mystery! I didn't pick it up so I couldn't guess on the weight.