... sometimes breaks, resulting in species sounding smaller or larger than expected for their size. A recent hypothesis suggests that allometry-breaking mammals cluster into two groups: those with anatomical adaptations to their vocal tracts and those capable of learning new sounds (vocal learners). Here, we...

... the acoustic properties of the vocal tract during song production. If motions of the beak are necessary for normal song production, then disrupting the ability of a bird to perform these movements should alter the acoustic properties of its song. We tested this prediction by comparing songs produced normally...