Song in the city: the effects of urban noise on communication patterns and population genetics

of an Australian passerine

Dr. Dominique Potvin Museum Victoria

Overview

• Introduction – Acoustic Adaptation

– Silvereyes

• Part I: Urban Silvereyes – The role of noise, morphology, genetics, meme use

and plasticity

• Part II: Island Silvereyes – The role of morphology, genetics, founder effects

and habitat

• Conclusions

Introduction: The Basics What is song?

• complex • learned trait • usually males • mate attraction, territory defense • dialects • Calls: not learned (innate?), used for contact/alarm, both sexes

Song Call

Introduction: The Basics

Acoustic Adaptation

• Morton 1975 • vocalizations should be modified to minimize degredation by environment

• HOW?

–sing simpler songs, avoid frequencies present in background noise

Nicholls & Goldizen 2006

Introduction: The Basics

what shapes a song?

Introduction: The Question

Part I: Urban silvereyes

• birds sing higher in cities: – great tits, blackbirds, song sparrows

• acoustic adaptation? – songs in the same frequency range

as urban noise (1-4kHz) may not be heard

– singing higher avoids masking (overlapping) by urban noise

…. BUT…???

Questions • are urban and rural silvereye

vocalizations different? (How?)

• possible mechanisms behind the change – Cultural evolution, plasticity,

morphological/genetic change

PART I : urban silvereyes

• abundant

• expansive range

• island colonization

• song 2-8 kHz

• DNA microsatellites

• three vocalization types

My study species: Zosterops lateralis

Methods – the field study PART I : urban silvereyes

• silvereyes sing AND call at a higher pitch in cities… and sing slower

Results

Potvin et al. 2011. Proc. R. Soc. B.

PART I : urban silvereyes

Silvereye sounds PART I : urban silvereyes

… How about alarm calls?

• Urban silvereyes have LOWER alarm calls!

PART I : urban silvereyes

Are urban silvereyes using different syllables?

• urban silvereyes use similar memes in songs: slower syllables, more trills

Potvin & Parris 2012. Ecol & Evol

Urban Rural

% trills

in s

ongs

PART I : urban silvereyes

Do urban silvereyes have their own city dialect?

• RDA: habitat features (urbanization, noise) predict 24% of repertoire similarity between populations

• this is comparable to geographic effects on dialect formation!

Potvin & Parris 2012. Ecol & Evol

PART I : urban silvereyes

What’s going on?

• Are city silvereyes evolving? • Can look at genetic differences, body size/shape differences

• Are silvereyes just really flexible? • Do they respond quickly to noise?

Are there morphological/genetic differences?

• high gene flow between urban/rural populations (Fst)

• urban silvereyes aren’t more or less inbred

• urban and rural silvereyes look pretty much the same

Potvin et al 2013. Evol Ecol.

Results • silvereyes won’t sing in captivity on demand

• silvereyes also don’t respond to playback in captivity

• two silvereyes won’t do much of anything in captivity

• conclusion: Silvereyes are uncooperative and difficult (albeit cute)

….but then…!

Methods – captive study

Results – the captive study

• silvereyes adjust calls immediately in response to noise – whether low OR high

Quiet Low F.N. High F. N.

Call

frequency (

Hz)

Potvin & Mulder Behav Ecol: in Press

Conclusions - Part I • urban and rural silvereyes are

morphologically and genetically similar

• urban silvereyes sing/call higher, are able to immediately adjust the pitch of vocalizations to avoid noise

= real time flexibility

• urban silvereyes use similar memes, and have possibly converging repertoires

= acoustic adaptation via cultural evolution!

Conclusions - Part I • THIS IS NOT A RULE

• alarm calls are LOWER in cities, and well-masked by urban noise

• maybe some changes are/seem maladaptive

– physiological, developmental effects of living in the city (i.e. stress when developing vocal apparatus)?

– different current predator risks in urban environment?

Part II – Island Silvereyes

• islands are ideal places to study song evolution: isolated populations should show rapid acoustic adaptation to environment

• can also consider the effects of genetic isolation/colonization, environment and connectivity on song dialect

Part II: Island Silvereyes

• Isolated populations should show rapid acoustic adaptation to their environments

• However, other factors can play into an island population’s dialect

– Cultural drift/founder effects

– Morphological/genetic changes

Questions • how does an island dialect develop?

– Are island repertoires well-suited to/predicted by their environment (Acoustic Adaptation)?

– how does morphology affect song?

– do song repertoires experience cultural drift and founder effects? Meme flow?

– are these associated with genetic founder effects?

PART II : island silvereyes

Methods: The island study PART II : island silvereyes

Results: The island study

• silvereyes on islands are BIGGER

• this size difference coincides with lower frequency songs, contact calls AND alarm calls

PART II : island silvereyes

Results: the island study

• island dialect similarity is predicted by habitat (.45), geographic proximity (0.32), genetic similarity (0.44)

• effective founder sizes of islands do not affect repertoire sizes (no evidence for repertoire bottleneck)

PART II : island silvereyes

Conclusions – Part II • island dialects may be affected by

morphology (affecting frequency)

• genetic connectivity & habitat both predict some level of repertoire similarity

• no evidence for lasting bottleneck or founder effects on song

PART II : island silvereyes

Discussion

• what factors contribute to the evolution of vocalizations? 1. morphology

2. genetics (?)

3. ENVIRONMENT

4. plasticity 5. sexual selection

Discussion

• environment plays a large part in the structure of vocalizations

• plasticity allows vocalizations to change: birds can be selective in their meme use (cultural evolution), adjust tempo or frequency real-time/within lifetimes

• sometimes, changes may appear maladaptive, must consider other possibilities

• also important to consider isolation, morphology and founder effects when analyzing song

A few interesting unanswered questions:

– how does city living affect development? stress

levels? song learning?

– exactly what syllables are kept in specific habitats? are different syllables “sexy” in different habitats?

– what are the implications for changed songs and calls in cities? Can rural and urban birds communicate effectively?

Acknowledgments • Supervisors: Raoul

Mulder, Kirsten Parris

• Jeremy Kruckel

• Many many banders, local experts and rangers

• Academic help: Mick McCarthy, Henrik Brumm & lab; Sonya Clegg; Gonçalo Cardoso; Evolution and Behaviour Group at U of M

• Funding: Holsworth WRF, Birds Australia (Victoria, Tasmania and national groups, now Birdlife), Australian Geographic Society, University of Melbourne

…. Questions?