Effects of urban noise on vocalisations of tūī (Prosthemadera novaeseelandiae) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology at Massey University, Auckland, New Zealand
Loading...
Date
2015
DOI
Open Access Location
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Massey University
Rights
The Author
Abstract
The two most important functions of avian acoustic communication are territory
defence and mate attraction. As such the effective communication of these signals
is critical for individual reproductive success. However if these vocal signals are
masked by anthropogenic noise, their signal efficiency is reduced and this may
result in direct negative fitness consequences. Therefore knowledge on how urban
habitat features including anthropogenic noise affect avian vocal communication
is important in understanding the evolution of animal communications in urban
ecosystems. Such knowledge is also important for the management of endangered
and declining species in urban areas.
Little is known about how birds respond to the highly variable levels of urban
noise in urban habitats. In this study I investigated spectral and temporal
differences in songs between populations of tūī (Prosthemadera novaeseelandiae)
in urban habitats with both high noise levels (near motorway) and lower noise
levels (distant from motorway). Male long-range tūī songs were collected during
the breeding season (October 2012 to February 2013) at three paired sites, with
one of each pair situated within 100m of a motorway and the matching site within
2-3 kilometres from the first site and the motorway. Urban noise levels (dB) were
measured at all sites. I compared motorway and non-motorway urban songs to
determine whether tūī shift the frequency, duration, trill components and output of
songs in response to anthropogenic noise. Songs were also recorded at two paired
non-urban sites over 50 kilometres from the urban sites (Mahurangi Regional Park
and Wenderholm Regional Park) and spectral characteristics were also compared
between these non-urban and the urban sites. I compared song rate and singing
rate to investigate whether song output varied with noise levels and between urban
and non-urban habitats. Through comparison of the degree of syllable sharing and
proportion of unique syllables and phrases at these sites, I explored the presence
of song dialects at urban and non-urban sites.
From 63.5 hours of field sampling, I collected a total of 1017 long-range
broadcast songs (627 songs from motorway sites and 390 songs from nonmotorway
sites). A significantly higher minimum frequency was found in songs
III
from the noisier, motorway sites compared with those from non-motorway sites.
Motorway songs had shorter song durations and decreased syllable diversity than
non-motorway songs. There were also a significantly lower proportion of trills in
the songs at sites near to motorway. As predicted a smaller syllable repertoire size
was found in the sites near the motorway compared to repertoires at nonmotorway
sites.
The presence of site-specific syllables and phrases and site-specific clusters in a
Ward cluster analysis, as well as a reduced degree of syllable sharing between
urban sites indicated the formation of local dialects in these fragmented urban
sites.
This study has provided data of bird song variation within urban ecosystems of
varying noise levels. These findings aid our understanding of modifications to tūī
songs to avoid the masking effects of low frequency traffic noise. Song duration,
trill proportion and repertoire size have all been demonstrated as being subject to
sexual selection. Changes in these aspects at noisy urban sites are considered
adaptations to urban effects. Such changes may have further implications for other
important behavioural aspects such as mate choice and can have profound effects
on tūī population dynamics between urban fragments. Understanding these urban
effects on bird songs and other important behavioural aspects are important not
only for advances in ecological theory in urban ecology, but also for conservation
management of urban habitats. For example, dialects between urban fragments
may create a reproductive barrier for dispersing birds, therefore reducing gene
flow between sites. Habitat corridors should be considered in urban designs, not
only to increase gene flow of species with poor dispersal ability, but may also
help to connect populations of highly mobile species such as tūī.
Description
Keywords
Tui, Vocalisation, Behavior, Birdsongs, Research Subject Categories::NATURAL SCIENCES::Biology::Organism biology