From PLOS
August 27, 2019 -- Crows can voluntarily
control the release and onset of their calls, suggesting that songbird
vocalizations are under cognitive control, according to a study published
August 27 in the open-access journal PLOS Biology by Katharina Brecht of
the University of Tübingen [in Germany] and colleagues.
Songbirds are renowned for their
acoustically elaborate songs; these show a degree of flexibility, potentially
indicating that they are under conscious control. However, the observed
variability in vocalizations might simply be driven by involuntary mechanisms,
and need not be based on cognitive control. In the new study, Brecht and
colleagues directly tested the idea that songbirds deliberately control their
calls, in the sense that they can be emitted or inhibited at will, as opposed
to being knee-jerk responses to food, mates, or predators.
The findings show that trained carrion
crows (Corvus corone), songbirds of the corvid family, can exert control over
their calls in a goal-directed manner. In a detection task, three male carrion
crows rapidly learned to emit calls in response to a visual cue (colored
squares) with no inherent meaning ("go-trials"), and to withhold
calls in response to another cue. Two of these crows were then trained on a
task with the cue colors reversed, in addition to being rewarded for
withholding vocalizations to yet another cue ("nogo-trials").
Vocalizations in response to the
detection of the go-cue were precise timed and highly reliable in all three
crows. The crows also quickly learned to withhold calls in nogo-trials, showing
that vocalizations weren't produced by an anticipation of a food reward in
correct trials. According to the authors, further work is needed to evaluate
the neurobiological basis of such cognitive vocal control in birds.
"Our study shows that crows can be
thaught to control their vocalizations, just like primates can, and that their
vocalizations are not just a reflexive response. This finding not only
demonstrates once again the cognitive sophistication of the birds of the crow
family. It also advances our understanding of the evolution of vocal
control."
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