Highlights•Low-amplitude signalling is a common but understudied form of
communication.•These signals can be both structurally and functionally distinct from loud …

Body size is a key sexually selected trait in many animal species. If size imposes a physical
limit on the production of loud low-frequency sounds, then low-pitched vocalisations could …

Songbirds often sing at higher frequency (pitch) in urban, noise-polluted areas, which
reduces acoustic masking by low-frequency anthropogenic noise. Such frequency shifts …

The avian bill is finely adjusted to foraging ecology and, as part of the vocal tract, it may also
affect sexual signals such as songs. Acoustic theory predicts that larger bills lower the …

Spectral and temporal measures of vocalizations have been found to correlate with physical
parameters that affect the fighting ability in various species of frogs, mammals, and birds …

The behavioral literature contains inconsistent results on the function of sound frequency
(pitch) across species, offering an unexplored opportunity to investigate evolutionary …

Acoustic properties of vocalizations arise through the interplay of neural control with the
morphology and biomechanics of the sound generating organ, but in songbirds it is …

Highlights•Animals in urban environments often produce higher-frequency
sounds.•Frequency differences of urban and rural birds persisted in a quiet, common …

Many animals use low frequency and harsh sounds in aggressive contexts. Low frequencies
are correlated with body size in some species, and thus can provide an indication of fighting …

Certain vocal signals can be difficult or challenging to produce due to constraints on vocal
mechanics. In the case of birdsong, both body size and beak morphology have been shown …