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.