The rapid expansion of urban environments is something to behold, and it may be causing adaptations in the natural world in unexpected ways.
It is clear to see that in recent decades urban areas have greatly expanded at unprecedented rates. With the growth of cities, it is advantageous to develop anatomical or behavioural adaptations to suit these new environments. You may not even notice that these changes are happening, but it is surprising to see how organisms have learnt to alter the way they live to cohabitate alongside us. City life is one of the most competitive lifestyles out there – not only in terms of business success, but also in terms of survival. This article will bring to light examples of the incredible adaptations’ organisms have developed for city life.
1. The Carrion Crow (Corvus corone)
With a population of 1,091,407  the city of Sendai in Japan is a sprawling metropolis. Living among the people are large populations of Carrion crows (Corvus corone) (figure 1). Part of their diet consists of nuts, which can tend to be tricky to open due to their hard shells. These crafty crows have come up with an ingenious way to overcome this – cars. People have reported seeing crows place nuts on the road and wait for a car to drive over them and crush the external shell. The first sightings of this behaviour were in 1975 at a driving school, but since then the carrion crows adaptations have spread further afield throughout Sendai . However, this is not just dumb luck, it has been shown that the crows know exactly what they are doing and have established quite the technique. They have been shown to wait for a car to be stopped at a traffic light, before placing the nut on the road and waiting for the oncoming stream of traffic to hopefully crack it open. They then wait for the next stop signal to recover their reward. This is not all though; if they place their nut on the road and it does not get run over after a few attempts they will reposition it in the hope of bringing more success . This is a perfect example of urban exploitation. Before cars were around, these crows would have cracked their nuts open by dropping them from a great height, however this did not always work. By using cars, the crows have a higher success rate, without having to exert themselves anywhere near as much.
2. The Peppered Moth (Biston betularia)
The industrial revolution was a monumental period, in which urbanisation grew at an incredible pace. Along with the rapid development of new machines and factories came immense amounts of soot pollution. This form of pollution covered almost every surface in industrial environments in a layer of black soot. The peppered moth (Biston betularia) before this period, was mostly white in colour with black flecks adorning its surface . The contrast of the moth on the black surfaces of cities at the time caused them to become easy pickings for potential predators. A random mutation within the species arose and quickly became common during this time. This mutation is known as ‘carbonaria’, which causes the moths affected to be much darker in colour  (figure 2). This was advantageous as it provided perfect camouflage to reduce predation occurring and increased the chance that the moths with the advantage would be able to breed. The frequency of this form of melanic peppered moth has since decreased in recent years . One may assume that this is due to cities no longer having a layer of smog shrouding every surface and concealing these melanic moths as was the case in the early 20th century. This shows how complex and effective natural biological mechanisms are, and how they work in real time.
3. The Cliff Swallow (Petrochelidon pyrrhonota)
A risk to both humans and other species alike – speeding cars are a threat to be wary of. If only there was some way to reduce the likelihood of becoming their victim? Well, the Cliff swallow (Petrochelidon pyrrhonota) (Figure 3)has just that. In southwestern Nebraska, these birds nest close to roads and it was common to see them as roadkill. However, a study was conducted by Charles Brown and Mary Brown in 2013  that found a significant decline in the number of cliff swallows discovered on the side of the road between 1983 – 2012. What was causing this change? It was discovered that the swallows that were found as roadkill had significantly longer wings than the rest of the population. Over the period of the study, it was observed that the average wingspan of these birds declined, meaning the individuals that did not follow this trend had a higher probability of becoming roadkill. Birds with shorter, more rounded wingtips can take off at a much more vertical angle than those with longer more pointed wingtips . So, if a cliff swallow is on the road and a vehicle is coming towards it at great speeds, the individuals with shorter wings and rounded tips will be able to evade collision more frequently. This concept is similar to the peppered moth mentioned above, as it is a trait that increases due to natural selection.
These are just three examples of how nature has developed adaptations to tackle urbanisation. It may be intelligence based – as seen in the crows of Sendai or based on natural selection – as seen in the other two cases. However these changes may occur, I think we can all agree that the way the natural world changes and constantly adapts is inspiring. It will be interesting to see how natural adaptations continue to occur as the human race develops and changes the very planet on which we all exist. I think that seeing how the expansion of urbanisation does not only affect people; but creates a ripple effect which travels through every species on earth is definitely something to be aware of.
Related Articles on Adaptation and Urbanization:
 Nihei, Y., and Higuchi, H., (2002). ‘When and where did crows learn to use automobiles as nutcrackers?’ Tohoku psychologica folia, 60(n/a), pp.93-97.
 Nihei, Y., (1995). ‘Variations of behaviour of Carrion Crows Corvus corone using automobiles as nutcrackers.’ Japanese Journal of Ornithology, 44(1), pp.21-35.
 Cook, L. and Saccheri, I., 2012. The peppered moth and industrial melanism: evolution of a natural selection case study. Heredity, 110(3), pp.207-212.
 Cook, L., Grant, B., Saccheri, I. and Mallet, J., 2012. Selective bird predation on the peppered moth: the last experiment of Michael Majerus. Biology Letters, 8(4), pp.609-612.
 Cook, L., (2003). ‘The Rise and Fall of the Carbonaria Form of the Peppered Moth.’ The Quarterly Review of Biology, 78(4), pp.399-417.
 “ Peppered Moth (Biston betularia) ab.carbonaria” by Bennyboymothman is licensed under CC BY 2.0
 Brown, C. and Brown, M., (2013). ‘Where has all the road kill gone?.’ Current Biology, 23(6), pp.233-234.
 Swaddle, J. and Lockwood, R., (2003). ‘Wingtip shape and flight performance in the European Starling Sturnus vulgaris.’ Ibis, 145(3), pp.457-464.