Cover photo: Birds on a lantern post (Source: Business Insider)
Taking a walk through the busy streets of the city, life appears to all around us. Bikers briskly pass you by, drivers honk loudly and hundreds of people walk around as if you find yourself in a busy anthill. A pigeon quickly takes off before a food-courier rushes past. A sea gull tries to snatch a piece of bread from a hungry student traveling home. When leaving the city center, the hustle and bustle becomes quieter. A family of ducks are crossing the road to join a group of geese in the pond. You listen carefully and hear the song of a blackbird as the sun slowly sets.
More birds than you’d think are in cities!
You may not realize it at first, but at least a fifth of all bird species worldwide also lives in our cities (Aronson, 2014). Even though populations can be small, a lot of bird species’ populations persist in urban areas amongst us people. No doubt they also have to navigate the same busy streets as we do, with the same sensory overload. Given the fact that this is not their ‘natural’ habitat, one could wonder how well these animals are doing in the cities.
A pair of pigeons (Source: Cool Green Science)
Scientists are now researching the ways some birds change their behaviors or appearance to cope with urban life. Some bird species alter how they sense the world and how they communicate. Hahs et al. (2023) found that all over the world, birds have similar traits when living in cities. They call this combination of characteristics the “urban trait syndrome”. They discovered that birds living in urban areas tend to eat a wider variety of food, lay fewer eggs, and are smaller than the rural birds of the same species. Birds also alter their communication in these noisy environments. For example, some species of urban-dwelling birds sing at higher frequencies and at a higher amplitude in cities than in rural areas (Slabbekoorn, 2003). This is mainly because the low frequency noises of the city (cars, aeroplanes, factories) can prevent some songs from being heard by other birds. The city noises become most problematic when birds sing at a similarly low frequency. Their song then gets ‘masked’ by the sounds of the city. Therefore, singing at a higher frequency and a higher amplitude can help the birds’ songs to be heard, something that is very important for reproduction or the defense of territory.
A bird in a city park (Source: Boudewijn Schreiner)
How can we manage cities to make them a better habitat for bird species?
Several bird species have adapted to cities, but not nearly enough. Bird populations have declined rapidly in the last century. For instance, North American bird populations have decreased by 3 billion birds since 1970 (Rosenberg, 2019). The global human population is only expected to increase, along with it the amount and size of urbanized area. This means that the pressure on birds will also increase, as their natural habitat decreases.
Many current urban bird populations are found in city parks or gardens. These are green areas amongst the otherwise concrete environment of the city. Cities with the highest number of parks and gardens (and the least amount of urban area) tend to have the highest density of bird species (Aronson, 2014). Those cities that harbor native plants are also favorable. Also, cities with many small parks tend to be better for diversity than those with fewer larger parks (La Sorte, 2023). Increasing the number of city parks could help increase bird species diversity and density. Planting native, non-invasive plant species in small parks can provide ample, preferred food sources. A reduced level of noise and light pollution could also help urban bird populations. Switching to green lights at night could help nocturnally migrating birds to not get as disoriented as they do with red and white lights (Poot, 2008). To reduce noise pollution, sound barriers or noise restrictions can be set in certain bird-rich areas. Encouraging the use of quieter machinery and equipment could also help with daytime noise pollution.
Managing cities to make them more welcoming towards birds will help increase bird diversity and abundance. It is time to make some necessary changes to cities in order to increase biodiversity!
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Green Light for Nocturnally Migrating Birds on JSTOR. (z.d.). www.jstor.org. https://www.jstor.org/stable/26267982#:~:text=We%20found%20that%20nocturnally%20migrating,the%20case%20on%20overcast%20nights
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La Sorte, F. A., Clark, J. A. G., Lepczyk, C. A., & Aronson, M. F. J. (2023). Collections of small urban parks consistently support higher species richness but not higher phylogenetic or functional diversity. Proceedings – Royal Society. Biological Sciences/Proceedings – Royal Society. Biological Sciences, 290(2006). https://doi.org/10.1098/rspb.2023.1424
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