We Have A Squirrel's Nest!

In our backyard are a cluster of trees. One has this perfect circular hole. 

 

 

 We never paid it any attention until one day a squirrel scurried inside it. Over the next few days, we've seen it hanging out it's head looking around.

 

 A squirrel's nest, 20 feet from our own nest. She must be a mama, just look at her face!