Field studies aren't always as neat and tidy as studies in the lab. There are a lot of things you just can't control; weather, animals, UFO landings, etc. For example, another master's student in my major had a plot out in the west desert for over a year. His degree rested upon the data that plot would generate. It was happily generating data for him until it was burnt up in a wild fire one afternoon this summer.
Needless to say, I have had passing panic attacks that something tragic would happen to my study plots. It came last week in the form of a badger. The rascal dug up a few of my plots in Washington. Note the faint pink string to the right of the holes. If he had been just slightly to the other side of that string, no damage would have been done. This is going to throw a wrench in my statistics.