Fidelity of vocal mimicry: identification
and accuracy of mimicry of heterospecific alarm calls by the brown
thornbill
- Division of Evolution, Ecology and Genetics,
Research School of Biology, The Australian National
University, Canberra, Australia
-
Correspondence: B. Igic, Building 116, Division of Evolution,
Ecology and Genetics, Research School of Biology, The
Australian National University, Canberra 0200, Australia.
-
m("gmail.com","brani.igic");">
Avian vocal mimicry has been studied for
decades, but little is known about its function or requirements
for accurate imitation. Furthermore, progress is hampered by the
difficulty in identifying which vocalizations are indeed
mimetic. We tested historical claims of vocal mimicry in the
brown thornbill, Acanthiza pusilla, using a
combination of human and computer methods to identify mimicry,
followed by comparisons of acoustic similarity with model
vocalizations. We recorded vocalizations of brown thornbills and
sympatric heterospecifics while undisturbed and during mist net
capture or the presence of natural or model predators. We then
cross-validated human classification of mimicry with computer
classification based on spectrographic measurements and spectral
cross-correlation. Finally, we quantified the accuracy of the
most common imitations. Brown thornbills predominantly imitated
alarm calls given by heterospecifics towards aerial predators,
which function in these models to provoke immediate flight by
receivers. Human and computer-based methods produced consistent
results when identifying and classifying mimicry. Mimicked
aerial alarms were not perfect imitations of their corresponding
model alarms, but did retain specific acoustic properties
previously shown to be important for provoking immediate alarm
responses. Although less accurate mimicry may reflect
physiological constraints, we suggest that mimetic function,
perhaps startling predators, only requires mimicry to retain
features of model alarms that provoke immediate alarm responses
by receivers. Understanding what factors influence the acoustic
structure of mimetic vocalizations is essential in understanding
the evolution of vocal mimicry, particularly with accumulating
evidence that mimetic function does not always require perfect
resemblance in other sensory modalities.
Highlights
► We evaluated vocal mimicry in the brown thornbill. ► Brown
thornbills predominantly imitated other species' aerial alarm
calls. ► Imitations were similar but not identical to
corresponding model alarms. ► Inaccurate imitations retained
features important for immediate alarm response. ► We suggest
alarm calls may not require perfect imitation for function.
|
|
