the motivation hypothesis was a competing hypothesis of the anti-exhaustion hypothesis. the motivation hypothesis, proposed by weary in 1988, explained that drift may be due to a lack of motivation to keep singing the same song, not because of neuromuscular exhaustion. this study also worked with great tits, playing song to them during the day. weary suggested that if drift was due to a lack of motivation, then if a bird was presented with the song of a rival, for example, then the bird should be able to increase its song output because of the motivational stimulus.