Comparative data sets with measurements of tonality and frequency range in passerines and hummingbirds

Upper vocal tract articulatory movements are a key component of vocal communication across birds and mammals. In many birds, tonal song arises from dynamically adjusted filtering of harmonic content. Many aspects of these upper vocal tract movements, such as the dynamics, motor control and relation to vocal learning, are poorly understood. Here we compare use of dynamically adjusted filter properties between vocal learners and non-learners to assess whether articulation in the upper vocal tract is linked to the increased neural substrate that evolved with vocal learning. We hypothesize that vocal learning ability is associated with enhanced ability for articulatory movements in the upper vocal tract. To test this hypothesis, we compared vocal learners and non-learners from two groups (186 passerines and 42 hummingbirds) by assessing tonality of song syllables. The data suggest that vocal learners in both clades employ more consistent broadband dynamic filter tracking than the non-learners, which contributes to the higher tonality in songs. In addition, oscine songs display higher tonality than those of hummingbirds. A complex interplay of vocal tract biomechanics, histological differences of the sound source as well as increased motor control through vocal learning facilitates more consistent generation of tonal song.