Today in class, we have learnt about urban animal diversity and how the process of urbanisation has threatened or benefited some species, particularly light and noise pollution. The effects of pollution on urban animals are rather well-known from many research works. Even Max and Samantha have written their opinions on living near a loud highway and the effects of anthropogenic noise on acoustic communication in different animals respectively. However, many of these research works only consider the effects of light pollution or noise pollution in isolation. Has anyone ever wondered which form of pollution is more detrimental to wildlife? Sadly, there are very few related research done and hence, there are a lot of controversies.
In this post, I would discuss about the effects of light and noise pollution on songbirds and their calls. This paper by Miller (2006), which was brought up in class today, discussed the effects of light pollution on the singing behaviour of American Robins. As predicted, birds breeding in areas with large amount of artificial light will sing earlier in the day than those in areas with low artificial night. Birds would also sing earlier within a site on brightly lit night. All these results strengthened our understanding on the effects of light pollution on bird calls.
However, there was another paper published that countered the discussion points brought up by Miller. This paper by Fuller et al (2007) argued that daytime noise predicts nocturnal singing in the European Robins and that noise pollution is a stronger factor that affects the time of bird calls. Their results showed that even though nocturnal singing of this diurnal bird did occur primarily in strongly lit areas, it was limited to areas that were also noisy during the day and was absent in most well-lit places that were relatively quiet during the day. This translated that daytime noise in the area had much greater effect on nocturnal singing activity than night-time light levels.
One reason for nocturnal singing is that urban noise frequency coincides with that of the robins, which is approximately 2–9 kHz. This bird may sing at night to reduce the total time spent singing against acoustic competition. Or these intelligent birds take the advantage of quieter conditions during the night to give additional signalling.
However, which form of pollution is more detrimental on bird calls would depend on the species. Noise pollution may be a greater factor than light pollution in explaining the nocturnal singing of European robins as compared to the American robin due to the difference in their size and hence, probably the frequency of their calls. American robins (23 to 28 cm) are generally larger than European robins (12.5–14.0 cm), and so they call at lower frequency by the law of physics. Such differences in the call frequency may be differentially cancelled out by urban noise, hence rendered the ability for calls to reach far. As such, to answer the question of which form of pollution is more impactful to the calls of songbirds would depend mainly on the species that is being investigated.
Dewey T. & Middleton C. (2002). Turdus migratorius. Animal Diversity Web. University of Michigan Museum of Zoology.
Hume R. (2002). RSPB Birds of Britain and Europe. London: Dorling Kindersley, pp. 263.
Miller W, M. (2006). Apparent Effects of Light Pollution on Singing Behavior of American Robins. The Condor 108, 130 – 139
Richard A, F., Philip H, W., & Kevin J, G. (2007). Daytime noise predicts nocturnal singing in urban robins. The Royal Society, 3(4).