Thanks Robin, very
interesting. The Blackbird alarm call that the Brown Thornbills in
my garden mimic is accurate enough that I certainly can't tell the
difference (until they follow it with their own call).
John Brannan
On 5/03/13 8:49 AM, Robin Hide wrote:
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.
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