Our population is expanding, and there’s no doubt about it. As cities continue to grow and impose on habitats, we really need to know exactly how wildlife is adjusting to the new challenges of metropolitan life. Being widespread and conspicuous, bird species make excellent models for studies looking at the effects of environmental change. In particular, comparisons of city bird behaviour with that of birds living in more rural areas give us good insights into how our activity is shaping the lives of the animals that live among us.
For me, the word “city” instantly brings to mind images of noisy traffic jams, heavy smog, towering buildings and dazzling lights. There are countless examples of city features that are affecting wildlife in some way, but for the purpose of this short article, I’m going to pick just two.
From smart-phones to streetlamps, our modern “24/7” lifestyles mean that artificial light is all around us. And it is no secret that exposure to unnatural light is having impacts on our natural “circadian rhythm”, or body clocks – causing disruption to our sleeping patterns (Dijk, 2013). Recent research shows that the similar may be true for birds; city blackbirds (Turdus merula) have been rising earlier and starting their daily routine before that of blackbirds in the countryside (Dominoni et al., 2013). It is thought that light pollution is the leading factor in causing city birds to awaken during “true night” rather than at dawn.
Light pollution is not the only city feature that is having notable impact on bird behaviour. Traffic and construction noise has the potential to drown out bird vocalisations – making communication by sound virtually impossible. Taking male birdsong as an example, we can see how this is significant. Male song is essentially a coded message that does two things: 1) give information to female listeners on his quality as a mate and 2) tell rival males to go away. If these messages cannot be heard properly, then it is likely that it will be much harder for the singer to find a female, and he will be more likely to get into more physical fights during disputes over territory.
However, some birds have adopted what is thought to be a smart strategy for ensuring song notes can be heard above the racket. Many comparisons of song from noisy urban areas with that from quiet countryside locations have shown the urban songs of some species such as the great tit (Parus major) to be at a significantly higher pitch than those in the countryside – making themselves heard over low frequency traffic noise (Mockford & Marshall 2009). So far, this has been seen in many species including: chiffchaffs (Verzijden et al., 2010), northern cardinals (Seger-Fullam et al., 2011), silvereyes (Potvin & Mulder, 2013) and song sparrows (Wood & Yezerinac, 2006).
From these two brief examples, it is clear that the noise and bright lights of the city are changing the behaviour of resident bird species. But do these changes in behaviour signify a more serious pressure on species’ survival? To answer this, scientists such as those at the Max Planck Institute for Ornithology (Seeweisen, Germany) are now looking into the physical consequences of living in a metropolitan environment for birds – particularly if exposure to anthropogenic (man-made) noise causes high levels of stress. Only once we know this, can we make predictions as to how life in the city might be affecting the survival of native bird species, and ultimately give us clues for the plans we should make in order to protect city wildlife as a whole. With a recent study showing a drop in the number of bird species found near noisy roadsides (Wiącek et al., 2015), further research cannot come too soon.
Dijk, D.J., (2013), Why do we sleep so late? Journal of Sleep Research, (22), 605-606.
Dominoni, D. M. ., Helm, B., Lehmann, M., Dowse, H.B., Partecke, J., (2013)., Clocks for the city: circadian differences between forest and city songbirds, Proceedings of the Royal Society of Biological Sciences, (282), DOI: 10.1098/rspb.2013.0593.
Max Planck Institute for Ornithology Website. URL: https://www.orn.mpg.de/en. [Last Accessed on: 10/02/2015].
Mockford E., Marshall, R., (2009), Effects of urban noise on song and response behaviour in great tits” Proc. R. Soc. Lond. B. (276), 2979-2985, ” DOI:10.1098/rspb.2009.0586
Potvin, D.A., Mulder, R.A., (2013), Immediate, independent adjustment of call pitch and amplitude in response to varying background noise by silvereyes (Zosterops lateralis), Behavioural Ecology, (24), 1363-1368.
Seger-Fullum, K.D., Rodewald, A.D., Soha, J.A., (2011), Urban noise predicts song frequency in Northern Cardinals and American Robins, Bioacoustics, (20), 267-276.
Verzijden, M.N., Ripmeester, E.A.P., Ohms, V.R., Snelderwaard, P., Slabbekoorn, H., (2010), Immediate spectral flexibility in singing chiffchaffs during experimental exposure to highway noise, Journal of Experimental Biology, (213), 2575-2581.
Wiąceka, J., Polaka, M., Kucharczyka, M., Bohatkiewiczb, J., (2015), The influence of road traffic on birds during autumn period: Implications for planning and management of road network, Landscape and Urban Planning, (134), 76-82.
Wood, W.E., Yezerinac, S.M., (2006), Song sparrow (Melospiza melodia) song varies with urban noise, The Auk, (123), 650-659.