NATURE
Wild Australia
SEPTEMBER. OCTOBER 2019PHOTO CREDIT: SHUTTERSTOCKJOHN PICKRELL
is a former AUSTRALIAN GEOGRAPHIC editor.
Follow him on Twitter: @john_pickrell34 Australian Geographic
B
IRDSONG ISN’T
just beautiful
to the human
ear. Often complex
and melodic, it’s a
vital tool used by
species such as
European robins, Australian magpies
and silvereyes to communicate with
one another, aiding reproduction and
survival. Birds with powerful, vibrant
songs are more likely to attract mates
and protect territories from intruders.
We already knew conventional
pollution, such as plastics and chemi-
cals, poses a problem to urban wildlife,
but it turns out that – for birds at least
- noise pollution is also insidious.
Several studies have explored this
problem, with some even suggesting
noise pollution, from sources such as
traffic and industry, could be contrib-
uting to declining bird populations.
One new study, from Queens
University Belfast in the UK, found
that the behaviour of European
robins changed when they were
subjected to human-made back-
ground noises. Male robins sing to
compete with one another for
territory and nesting space, using
complex compositions to advertise
aggressiveness and fighting ability.
Combatants then make decisions
about conceding or defending
positions based on opponents’ songs.
But the din of urban environments
is making it ever harder for such
messages to be communicated,
meaning male robins may concede
too easily or fight too vigorously, says
Dr Gareth Arnott, a lead author on the
study, which was published in the
journal Biology Letters in June.
“We found that bird song structure
can communicate aggressive intent,
enabling contestants to assess their
opponent, but noise can disrupt this
communication by masking the
structural complexity of songs,” the
scientists wrote. “This suggests that
under noisy conditions, birds may be
limited in their ability to use song
complexity to defend or acquire
resources, such as territory.”
Gareth says the research shows
human-made noise pollution is
affecting wildlife more than we might
think, having unexpected implications
for how animals communicate – possi-
bly even affecting survival and popula-
tion numbers in some species.
But there’s evidence birds are fight-
ing back against the racket. Research
from the University of Melbourne
published in 2011 showed some urban
songbirds were singing more slowly,
loudly and at a higher pitch than
members of the same species living in
more rural or bushland environments.
Led by birdsong expert Dominique
Potvin, the researchers studied 14
silvereye populations across south-
eastern Australia, finding that urbanbirds sang and called at a higher pitch,
so they could be more easily discerned
above traffic and other background
noise. These changes were thought to
have been made through both learnt
behaviour in song composition and
evolutionary changes to the briefer
calls that birds made.
Some birds with naturally high-
pitched calls, such as the grey fantail,
may have little need to adapt their
calls because they can be clearly heard
above traffic. But research suggests
other Australian birds, including
rainbow lorikeets, eastern rosellas
and grey shrike-thrushes, are more
likely to sing at a higher pitch in
urban environments.
It’s not only bird communication
that suffers in environments plagued
by human-made background noises.
A study of western bluebirds, moun-
tain bluebirds and ash-throated
f lycatchers in Colorado, in the USA,
found that birds nesting near noisy gas
compressors had hormone levels
equivalent to those in humans suffer-
ing from post-traumatic stress disorder.
A 2018 paper published on the
work in the journal PNAS says this
may be because birds caring for
young were unable to detect signs of
predators above the noise, and were
therefore constantly on alert, eventu-
ally becoming exhausted.
Gareth says there are important
implications to consider around noise
pollution and wildlife protection.
When we think of bird conservation,
we now need to factor in background
noise levels, not simply find suitable
habitat with tree cover.Birds struggling to be heard
Noise pollution in urban environments is drowning out birdsong,
making it ever harder for birds to communicate.There’s so much in urban environments to
confuse birdlife, from windows and mirrors
to human-made noise.