I found a battered little yellow butterfly, Pyrisitia lisa, yesterday. Little yellows do not spend the winter here. They spend their winters far to the south of here, and re-populate the area every spring, riding the winds to travel the great distances needed to accomplish the task. There is no evidence of a southward migration in the fall. At least, that seems to be the prevailing opinion.
So some years we have large numbers of little yellows and some years we have none.