Some say it is the milder winter's, so the cold isn't killing them off. I don't know about that. We don't always get as much snow as ten or fifteen year's ago, but it still gets just as cold.
A buschcraft instructor once told me they are border dwellers. Long grass, fields, brush, etc. So a cut lawn is safe and proper forest is safe, but new growth, fields, paths, and the edges of forests are the danger zones. Don't know if it's true or not, but that would explain why parks here have more than the forest.