The song of the city, or how to compete with a highway
Stop and listen. What can you hear? The buzzing of a fish tank, the hum of cars, and the soft buzz of your computer or the overhead lights, a rumbling plane, a ticking clock. We live in an age synonymous with the unceasing song of technology. And this hasn’t gone unnoticed by wildlife.
Most man-made noise, from lawn mowers to the groan of industry, occurs at the low-frequency range of the spectrum (<3 kHz). Bird songs are masked when they overlap with this low-frequency urban grumble. To be heard, songbirds are changing their tune.
Singing a different song
Some birds have adapted to their new city life. By changing the frequency of their songs, birds can compete with the urban noise.
Australian Silvereyes not only sing higher and slower in urban habitats compared to rural environments, but they increase the frequency of their calls too.
And it’s not only Australian birds modifying their melodies. European Great Tits sing louder and higher in noisier habitats, while Common Nightingales croon louder when in the midst of heavy traffic. Male American Song Sparrows alter their songs only in the parts being masked by urban noise, singing higher and exerting less energy into singing the lower notes. Urban European Robins have almost sidestepped the issue, singing in the relative hush of the night instead.
Why do birds sing and call?
Birds learn these melodious songs from a young age for a few main reasons:
- Simply put, males sing to attract females. Attempting to allure females with the quality and number of their complex musical displays. As women may swoon over a French or British accent, birds sing in different dialects, and this can influence a female’s attraction to a male. Some birds also sing to maintain a bond with their mate.
- Birds can be highly territorial. To help actively mark and defend territories seasonally or year-round, they sing.
Birds also call to each other to communicate with flock-mates, coordinate flight and to alert others of food or predators.
Basically, birds call and sing to communication with each other. So it’s essential that their message be heard. If a bird’s song is obscured, their ability to entice female interest or keep a territory lessens. Though whether changing their tune impacts a male’s reproductive success has yet to be studied. Singing louder and higher heightens energy and oxygen use in Great Tits, which does negatively impacting their health.
How do birds change their tune?
Songs are learned, and so can change over time. But calls are innate, developing from begging calls as a chick.
Many species have shown behavioural plasticity, changing their songs under the pressure of the city noise to better suit their surroundings. But Silvereyes have also modified their innate contact calls. This suggests that there may be changes occurring genetically across the generations of city dwellers, or during early development.
The urban-rural divide
The urbanization and industrialization of the world has changed the soundscape phenomenally, creating a novel stage for wildlife. Some have flourished in their new concrete habitats. But not all species adapt, and so can’t persist in an urban backdrop. As such, the diversity and density of songbirds in cities and around highways has diminished relative to quieter rural habitats.
As well as spatial separation, rural and urban birds are becoming more and more vocally distinct as urban birds attune to the city soundtrack. Great Tits from rural environments respond less to urban songsters during territorial invasions than to their rural kin. And the same pattern occurs for urban dwellers.
If urban and rural birds lose the power to communicate, they may not recognise each other as the same species. If they can’t communicate, they can’t breed, and could diverge into different species entirely.
As our cities expand, the world gets busier and noisier. Our metropolitan life shapes not only the way we interact, but how wildlife communicates. Songbirds must adapt, or perish in the urban sprawl of modern life. Luckily, it sounds like some are doing just that.