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The evolution of acoustic identity signals in birds [Elektronische Ressource] / Hendrik Reers. Betreuer: Bart Kempenaers

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The evolution of acoustic identity signals in birds Dissertation Fakultät für Biologie Ludwig-Maximilians-Universität München durchgeführt am Max-Planck Institut für Ornithologie Seewiesen vorgelegt von Hendrik Reers Februar 2011 Erstgutachten: Prof. Dr. Bart Kempenaers Zweitgutachten: PD Dr. Volker Witte Eingereicht am: 17. Februar. 2011 Termin der mündichen Prüfung: 13. Oktober. 2011 Table of contents Summary ............................................................................................7 General introduction ...................................................................................11 Chapter 1 The effect of hunger on the acoustic individuality in begging calls of a colonially breeding weaver bird ............27 Chapter 2 Determinants of nest and individual signatures in tree swallows: A cross-fostering experiment ......................51 Chapter 3 Individual recognition and potential recognition errors in parent-offspring communication........................69 Chapter 4 Do zebra finch parents fail to recognize their own offspring? ..........................................................................93 Chapter 5 Sticking out of the crowd: The effect of acoustic similarity on recognition ................................................111 General discussion .....................................................................................125 Acknowledgements .....................

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Published 01 January 2011
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The evolution of acoustic
identity signals in birds



Dissertation


Fakultät für Biologie
Ludwig-Maximilians-Universität
München


durchgeführt am
Max-Planck Institut für Ornithologie
Seewiesen



vorgelegt von
Hendrik Reers
Februar 2011 Erstgutachten: Prof. Dr. Bart Kempenaers
Zweitgutachten: PD Dr. Volker Witte

Eingereicht am: 17. Februar. 2011
Termin der mündichen Prüfung: 13. Oktober. 2011
Table of contents

Summary ............................................................................................7
General introduction ...................................................................................11
Chapter 1 The effect of hunger on the acoustic individuality in
begging calls of a colonially breeding weaver bird ............27
Chapter 2 Determinants of nest and individual signatures in
tree swallows: A cross-fostering experiment ......................51
Chapter 3 Individual recognition and potential recognition
errors in parent-offspring communication........................69
Chapter 4 Do zebra finch parents fail to recognize their own
offspring? ..........................................................................93
Chapter 5 Sticking out of the crowd: The effect of acoustic
similarity on recognition ................................................111
General discussion .....................................................................................125
Acknowledgements ....................................................................................139
Author contributions .................................................................................141
Addresses of co-authors .............................................................................143
Summary
he focus of this dissertation is on the evolution of phenotypic variation T resulting not from natural or sexual selection, but from selection for
‘distinctiveness’. Historically, the main paradigms of evolutionary biology rooted
in natural and sexual selection trying to explain a large proportion of phenotypic
variation occurring between conspecifics; however, there are individual
differences that are left unexplained by these selective forces. Some of these
phenotypic differences allow individuals to recognize each other by making its
bearer distinguishable from others. Distinctiveness is a selective advantage
whenever two individuals benefit from repeated interactions, but face the risk of
mistaking one individual for another.
Individual recognition has been demonstrated across many taxa and in
different sensory modalities. Probably the best known and most impressive
example, illustrating the benefits of individual recognition, are breeding colonies
of birds. In a penguin colony of thousands, without landmarks or nests and over
constant background noise from hundreds of conspecific young, a chick is able to
recognize its parents by call even after weeks of separation. The ability of chicks
and parents to recognize each other using complex contact calls is a fascinating
communication system to study the evolution of identity signals.
In this dissertation, I set out to answer questions about different aspects of
identity signalling from a signaller’s and a receiver’s perspective in different
songbird study species. The first two chapters examine from a signaller’s
perspective how acoustic parameters can be influenced by a chick’s condition as
well as by its genetic background and rearing environment. First, I present
findings on the influence of hunger on the acoustic individuality in begging calls
of nestlings of colonially breeding weaver birds (Chapter 1). Our results
demonstrate for the first time how acoustic individuality is preserved in calls
while simultaneously indicating a chick’s hunger to its parents. These findings
further suggest that familiarity with a chick’s begging calls has the potential to
increase the parents’ assessment of a chick’s hunger state. Summary 8
After finding that condition (i.e. hunger) can influence certain acoustic
parameters while others remain stable, we investigated the influence of genetic
background and environmental influences on these parameters in a cross-foster
study on wild tree swallows (Chapter 2). Siblings within a brood often share a
common acoustic features referred to as brood signatures. In our study we found
that nestlings that were raised by their biological parents showed a brood
signature, while calls of cross-fostered nestlings did not, neither for their nest of
rearing nor for their nest of origin. On the level of acoustic parameters, our study
revealed that variation in specific call parameters can be partly explained by effects
due to a common origin (e.g. genetic effects) while others by the rearing
environment (e.g. social interactions) of the nestlings.
The studies of the next three chapters adopt a receiver’s perspective and
investigate the accuracy of individual recognition, and why and when individuals
commit recognition errors. In a laboratory study on zebra finches, I demonstrate
that fledglings are able to identify their parents by contact calls (Chapter 3).
However, fledglings do not exclusively respond to their parents, but respond also
to unrelated adults, suggesting that fledglings make recognition errors, possibly
related to the acoustic similarity of adult individuals. Surprisingly, in playback
experiments with calls of own and unrelated young, zebra finch parents, did not
seem to respond primarily to contact calls of their own fledglings (Chapter 4).
This suggests that parent-offspring recognition is either a one-sided process or
that parents avoid vocal contact under situations such as simulated by our
playback setup.
Following the finding from chapter 3 on a potential relationship between
acoustic similarity and the likelihood for recognition errors, we tested this
hypothesis in a large scale playback experiment with zebra finches (Chapter 5). By
presenting a series of adult calls of know similarity to fledglings, we were able to
demonstrate that acoustic similarity is related to ‘false responses’. This finding
demonstrates for the first time that acoustic similarity in contact calls of birds can
cause recognition errors. Collectively, our results provide support for the
hypothesis that evolution for distinctness is driven by negative-frequency
dependent selection.
The evolution of acoustic identity signals in birds 9
In summary, in this dissertation I present several novel findings on the
evolution of acoustic identity traits in birds, with a special focus on parent-
offspring communication. I present novel insights on how vocalizations are
influenced by condition, environment and genes, and which acoustic parameters
are used to form unique identity signatures. Furthermore, I provide first
experimental evidence for the role of acoustic similarity for recognition errors in
birds, supporting the importance of negative-frequency dependent selection for
the evolution and spread of individual signatures.