I believe that this question is meant to be asked during a person's first read of the book. It's tough for me to answer it completely truthfully because I know what is happening to the construction site. It's also an opinion-based question, so you can feel free to state your opinion about what you think is happening to the construction site.  

The construction site in question is the future site of a new pancake house restaurant. Construction crews keep being delayed because the survey stakes keep being pulled up during the nights. Other oddities that are happening at the site are things like baby alligators being found in the outhouses and vehicle tires being flat.  

When I read the book the first time, I suspected teenagers of some kind. The above things just sound like things bored teenagers would do together. Admittedly, the alligator thing is very odd, but kicking over survey markers and slashing tires sounds like angst-filled teenagers to me. The book provides a likely character, too—Dana Matherson. Readers eventually come to discover Mullet Fingers is the culprit, and he is doing all those things to protect the owls.