Under the USGA rules, a birdhouse is considered an immovable obstruction because it is a permanent fixture on the course. And under Rule 16-1, a player only receives relief when a) the player’s ball touches or is in or on an abnormal course condition b) abnormal course condition physically interferes with the player’s area of intended stance or area of intended swing c) or only when the ball is on the putting green, an abnormal course condition on or off the putting green intervenes on the line of play.