The chickens pecked their way through the wood I have protecting the bottom part of the pen. There were able to get out and wreak havoc on the front area of the lawn. I have since fixed it. In the picture you can see the area they were able to get to in front of the bottom boards.
Looks like your board has rotted, watch the chicken wire, that will rust through in a couple of years. Chickens can be quite industrious in their digging.