If it is known or virtually certain that an outside influence (bird, animal or another player in stroke play events) lifted or moved a player's ball then there is no penalty and the ball must be replaced on its original spot or on a spot estimated to be its original spot. This applies whether or not the player's ball has been found.
Should it not be known or it is not virtually certain that the ball was lifted or moved by the outside influence and the ball is lost then the player must take a stroke and distance relief under Rule 18 (2) ( penalty of 1 shot and play again from spot where last played from)