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Asymmetrical song convergence in two hybridizing nightingales: The mystery of “doublespeaking” males

Authors:

Abstract

Nightingale species are considered among the most skilful song performers of European songbirds, by both the diversity of their song and their learning abilities. The common nightingale (Luscinia megarhynchos) and thrush nightingale (Luscinia luscinia) are two closely related species sharing a recent sympatric zone across central Europe. Interestingly, many thrush nightingale males in this contact zone develop a “mixed singing” strategy, copying parts or sequences of songs from the other species’ repertoire. Several hypotheses were proposed to explain the occurrence of such song convergence. First, evolution of mix-singing behaviour might be driven by female preferences for males with larger song repertoire, as shown in several other songbird species. Second, the two species have similar habitat preferences, and interspecific territoriality occurs in sympatry. Mixed singing may constitute an advantageous strategy if improved communication with common nightingales reduces the cost of competition between males. Last, mixed singing might simply result from misdirected learning of thrush nightingales, if not costly enough to be counter-selected. On the poster, we will present the first detailed comparison of the repertoire size between sympatric and allopatric thrush nightingale males, focusing on the song type diversity level. Apart from a direct additive effect of whole-song copying, analysis of song syllables show the integration of heterospecific syllables within typical thrush nightingale song types. Surprisingly, some sympatric males also display a higher rate of song “improvisation”, out of usual species repertoire. Furthermore, we will present spatial distribution of males in sympatric area and investigate the relationship between the extent of mixed singing and density of both species. Though the previous hypotheses would predict to find more mixed singers in close range of common nightingale locations, the actual territory partitioning seems more complex. We conclude by proposing some leads on further potential explanations for the occurrence of mixed singing.
Common Nightingale (CN) Thrush Nightingale (TN)
How do Thrush Nightingale songs differ
between allopatry and sympatry?
Is mixed singing a way to enhance male
repertoire size?
Is mixed singing occurrence influenced by
density of nearby Common Nightingales
Conclusion
The mystery of doublespeaking” males
Asymmetrical song convergence in two hybridizing nightingales:
Abel Souriau, Jiří Reif, Silke Kipper*, Jana Vokurková, Radka Reifová, Adam Petrusek, Tereza Petrusková
Mixed singing evolution shaped by…?
Small songbirds with a wide diversity of songs
Two recently diverged (1.8 Mya) sister species
with very similar habitat requirements
Sympatric zone across central Europe:
Thrush Nightingale is copying part of Common
Nightingale repertoire
Preliminary Results
Acknowledgement
Background
Shorter songs, lot of repetitions
Open learner, can copy song
types from CN neighbours
Sire most of the rare hybrids
captured in the wild
Methods
Spring 2015: Recording of Thrush Nightingale males in
both sympatry (N=9) and allopatry (N=9)
(Southern and Northern Poland)
Common habitat along bushy banks (Narew river, Northern Poland)
Czech Science Foundation grant 15-10884Y, Hana Kohoutová, Michael Weiß (Freie Universität, Berlin), Tomasz.S. Osiejuk (A. Mickiewicz Univ., Poznan), Paweł T. Dolata, Pavel Kverek.
Playback experiment on CN males in Sympatry:
aggressive reaction to pure-species and mixed songs?
Common Nightingale
Luscinia megarhynchos
Thrush Nightingale
Luscinia luscinia
Catalogue of song types: 162 song types found in
20 individuals from 6 populations
3 categories: typical songs, mixed songs and
improvisations (songs found only once)
mixed singing
Longer songs with characteristic
trill-endings
Open learner, able to copy song
types from both species !
Slightly larger size than CN (might
be dominant sp.)
0
5
10
15
20
25
30
35
1 2 3 4 5 6
Sympatry
Future plans
200m
Chocz 2015
Song types
Individuals
souriaua@natur.cuni.cz
Full mixed song
2
4
6
8
10
kHz
s
0.5 1 1.5 2 2.5
Questions
impro.
mixed
TN pure
Spatial distribution:
Territory of CN and TN males near Prosna river in Chocz, Southern Poland (2015).
Repertoire size: comparison between locations
Male territoriality: Interspecific communication
with neighbours could reduce competition cost?
? Learning “mistake”: recent behaviour leading to
non-adaptive behaviour? (hybrid depression cost)
Female preference: repertoire size and diversity
as a honest signal of male quality?
Playback experiment on captive female:
response to pure-species and mixed songs?
Investigation on full breeding cycle (fitness) with
territory and repertoire monitoring over years.
Mix singing enhance repertoire size:
but size isn’t higher than in allopatric population,
and proportions vary a lot among individuals
quality” of song type over “quantity”?
No clear link between mixed singing and
interspecific density
Mixed singing is more than simple “imitation”:
CN song copying + element integration in new songs
Only 7 TN for 29 CN over breeding season: very low density of TN for 2015
Local decline of population? CN locally dominant in competition?
Almost all TN proven to be mixed singers during the season
Important change in TN repertoire compared to past recordings (2008), unlike
allopatric population (2009) local population shift, migration event?
Faculty of Science, Charles University in Prague, *Technische Universität Munich
See also Poster 28
Song type diversity for a sample of 80 songs per male Thrush
Nightingale for both populations (allopatry + sympatry)
1 2 3 4
Allopatry
kHz
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s
0.5 1.5
1 2
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1 2 2.5 3 3.5
kHz
s
0.5 1.5
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kHz
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0.5 1 2
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1.5
kHz
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kHz
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Mixed-syllable song
Sympatry: mixed singing present in many repertoires (up to 1/3) Along
with improvisations, very variable proportion among individuals.
Allopatry: repertoire surprisingly as wide as in sympatry, with lot of
improvisations (= very rare songtypes + punctual association of elements).
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