Data from: Divergence in calls but not songs in the orchard oriole complex: Icterus spurius and I. fuertesi

Birdsong has important functions in attracting and competing for mates,
and song characteristics are thought to diverge rapidly during the process
of speciation. In contrast, other avian vocalizations that may have
non-reproductive functions, such as calls, are thought to be more
evolutionarily conserved and may diverge more slowly among taxa. This
study examines differences in both male song and an acoustically simpler
vocalization, the ‘jeet’ call, between two closely related taxa, Icterus
spurius and I. fuertesi. A previous study comparing song syllable type
sharing within and between I. spurius and I. fuertesi indicated that their
songs do not differ discernibly. Here we measured 18 acoustic
characteristics of their songs and found strong evidence supporting this
prior finding. In contrast, we measured 17 acoustic characteristics of
jeet calls and found evidence of significant divergence between the two
taxa in many of these characteristics. Calls in I. fuertesi have a longer
duration, a larger frequency bandwidth, a lower minimum frequency, a lower
beginning frequency, and greater levels of both frequency and amplitude
modulation in comparison to the calls of I. spurius. In addition, I.
fuertesi calls contain two distinct parts, while the calls of I. spurius
have only one part. Thus, we find evidence of divergence in the calls of
the two taxa but not their songs challenging the widespread assumption
that complex bird song evolves more rapidly than other types of
vocalizations. Understanding divergence in multiple vocalization types as
well as other behavioral, morphological, and molecular traits is important
to understanding the earliest stages of speciation.