The squeaky sounds of city living

Nature never feels further away than when you are in the middle of a city. Growling traffic, expanses of hot concrete and the countless tall buildings seem like another world far away from lush rainforests or tranquil mountain streams. You’d never think of a city as an ecosystem. Yet many animals have adapted to the hustle and bustle of the urban environment.
Birds and frogs use complicated songs to communicate with one another, usually to mark their territory or to attract a mate. Birds of the same species will often sing in different dialects just as we learn to speak in different languages. A study conducted in the US city of San Francisco has found the range of dialects sung by the white-crowned sparrow has changed over the past thirty years, while a study conducted by the University of Melbourne has found a similar change in frogs.
In both cases, the researchers wondered if the noise of the city influenced the species’ calls. Traffic, building construction and the effect concrete has on sound means the loudest noises in the city are low-pitched. Therefore high-pitched songs can be heard much more clearly.
In the American study, three different types of sparrow dialect were studied over three decades. The one with the lowest pitch disappeared by 1998, while the other two not only became more common, but seemed to increase in pitch when compared with their country cousins.
It’s unusual for bird dialects to change on their own so quickly, leading the researchers to believe the increasing noise of the city favoured white-capped sparrows who sang in higher pitches.
For frogs, the distance over which they can communicate can be reduced to as little as twenty metres if there’s noisy traffic around. To compensate, the males being studied seem to be croaking in a higher pitch to get the girls to listen. The question now is: do the ladies like the squeakier sounds?
Cities are important landscapes not just for humans, but for the animals who share it. While many species will adapt, and even thrive, others won’t do so well. It’s important to remember that nature isn’t always about forests, oceans and fields, but is often about what happens in our own backyard.