Birdsong struggles to be heard in urban environment
BIRDSONG 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 chemicals, 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 contributing 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 background 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 – possibly even affecting survival and population numbers in some species. But there’s evidence birds are fighting 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 urban birds 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, mountain bluebirds and ash-throated flycatchers in Colorado, in the USA, found that birds nesting near noisy gas compressors had hormone levels equivalent to those in humans suffering 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, eventually 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.
This article was published in Issue 152 of Australian Geographic. Purchase a copy here.