KOH Yeh Jie Wilson, Life Sciences Major – AY 2015/16

Impacts of traffic noise on the dawn chorus

Edward O Wilson identified five key threats to biodiversity. Of all human land uses, urbanisation exemplifies all of them better than perhaps any other, and so it has major environmental impacts. One of those impacts is noise pollution.

A major source of anthropogenic noise is road traffic, which clearly increases with urbanisation. The rate of urbanisation (100 %) in Singapore (SG) is unparalleled in the tropics, and despite laudable controls on vehicle ownership, the number of vehicles on SG’s roads increased by 50 % from 1970 to 2010. Compared to other forms of pollution, anthropogenic noise and its ecological consequences have received less research attention, but this is changing, with more studies documenting these even on plants (in one of my favourite studies ever). Traffic noise can degrade the quality of natural habitats, even far from roads, and impact the behaviour, physiology and reproduction of animals. For example, they may alter their vocalisations (pitch, volume, timing) to avoid auditory masking and there is experimental evidence that traffic noise can impair health and reproduction of birds.

Wilson asked how traffic noise affects the dawn chorus in SG – the first study to ask this question in the tropics. By dawn chorus, I mean the cacophony of bird song that occurs early each morning. For songbirds, singing really matters. It’s how they advertise to potential mates, with females often assessing the quality of males based on their songs, and establish the boundaries of their territories, for example. Various reasons have been proposed to explain why singing activity is most concentrated and lively at dawn. One is that it’s not bright enough to forage yet, but they don’t need light for vocal interactions, so they may as well sing. Another is that early morning is when a bird is most likely to have a surplus of energy but carrying around excess energy makes flight more costly, so they should use it to sing at a time when they won’t be able to forage effectively anyway.

recording the dawn chorus in Singapore

But if birds react to traffic noise by altering their singing, the result can be maladaptive. Wilson (who necessarily became quite the early bird himself) recorded the dawn chorus in forest patches near roads. He found no effect of traffic noise on the overall chorus, although changeable hawk eagles (Nisaetus cirrhatus) and olive-winged bulbuls (Pycnonotus plumosus) vocalised for shorter intervals on noisier mornings – a difficult result to explain.

Unexpectedly, three species, vocalisations by both of these species and two others, Asian-fairy bluebirds and pin-striped tit babblers, seemed linked to the cicada chorus in complex ways that suggest that these animals are timing sound production to take advantage of empty acoustic space (believe me, when many cicadas are stridulating in SG, the noise can be deafening).

Wilson currently teaches secondary-school biology.