Urban development is one of the major threats to biodiversity across the globe, yet some animals appear to thrive in our cities. To find out more about the ups and downs of city life, a team of scientists joined forces with 50 Barbados bullfinches for a series of experiments. What they found suggests that city birds are bolder, smarter, and apparently healthier. But does city life contain hidden costs?
Cities are expanding all around the globe, and this often leads to habitat loss and pollution as the surrounding countryside turns into suburban neighbourhoods. ALAN (Artificial Lights At Night), for example, drive insects away, which gives the birds that feed on them no other option but to leave as well [1]. However, some species like the rock pigeon have long been thriving in our cities, and many studies suggest that there might be differences between members of the same species depending on whether they live in urban or rural areas [2]. This idea is nothing new. Many of us will have read Aesop’s story about the city mouse and the country mouse, where the latter feels so scared after a close encounter with dogs in a human household that it swiftly returns to a peaceful existence in the countryside. Yet a 2016 study suggests that the situation looks very different for birds.
The researchers involved in this study wanted to find out which characteristics set urban birds apart from their country cousins, and how they adapt to make the most of this unnatural landscape. To investigate this question, the scientists caught 50 Barbados bullfinches from 8 different areas in their native range. These areas ranged from completely wild to urban settings, and as such represent all degrees of human contact that the birds would experience across the island. Firstly, the scientists tested how bold each finch was. Boldness was measured by offering birds a dish full of tasty seeds and measuring how long it took them to feed. This test was repeated three times, and then a novel object was placed next to the dish. Taken aback by this unfamiliar addition, some birds hesitated, and some didn’t approach the seeds at all, thus identifying them as more or less ‘neophobic’; scared of the new.
Scientists also measured the finches’ ability to solve problems by presenting them with two puzzles which they had to work out to gain treats. Using food to get animals interested in the tasks presented to them is a common technique to assess their intelligence, and many such experiments have been done on crows and jackdaws [3]. For these puzzles, bullfinches were given 15 attempts each, and the average time they took to get to the reward was used to measure their problem-solving ability. Lastly, the researchers assessed the birds’ immune response on their last day of captivity in order to learn more about their health. This was done by injecting the finches with a harmless substance and seeing how long it took their bodies to respond to its presence.
In the end, this experiment produced clear results: city birds are not only better than their wilder relatives at solving problems, but also have a better immune response. Urban bullfinches are also bolder, but unexpectedly more neophobic. These differences are striking if we think that they solely depend on the birds’ postcode, and they give us an insight on the compromises that animals need to make in order to endure human expansion. Another study discovered similar characteristics, like increased neophobia, in woodpecker finches living in harsh and unpredictable environments [4], suggesting that for many species city life doesn’t exactly pay off. Their quick immune response, for example, could also indicate that they are exposed to more pathogens [5], which most likely hide themselves in human waste.
Overall, this study furthers our understanding of how urban expansion is impacting birds, and suggests that cities present unique challenges that animals need to overcome before enjoying the perks of city life. If you want to make life easier for these intrepid birds, there are a number of things you can do. Avoiding littering and regularly cleaning bird feeders prevents birds from getting ill and infecting others. Additionally, switching light off after it gets dark is good to encourage insects and the animals that feed on them.
Translating Science article by Maria Giulia Checchi.
References
- Owens, A., Cochard, P., Durrant, J., Perkin, E., and Seymoure, B. (2019). Light Pollution Is a Driver of Insect Declines. SSRN Electronic Journal. https://doi.org/10.2139/ssrn.3378835.
- 2. Santini, L., González-Suárez, M., Russo, D., Gonzalez-Voyer, A., von Hardenberg, A., and Ancillotto, L. (2018). One strategy does not fit all: determinants of urban adaptation in mammals. Ecology Letters 22, 365–376. https://doi.org/10.1111/ele.13199.
- 3. Emily Faun Cory (2016). The Rooftop Raven Project: An Exploratory, Qualitative Study of Puzzle Solving Ability in Wild and Captive Ravens.
- 4. Tebbich, S., and Teschke, I. (2014). Coping with Uncertainty: Woodpecker Finches (Cactospiza pallida) from an Unpredictable Habitat Are More Flexible than Birds from a Stable Habitat. PLoS ONE 9, e91718. https://doi.org/10.1371/journal.pone.0091718.
- 5. Albery, G.F., Carlson, C.J., Cohen, L.E., Eskew, E.A., Gibb, R., Ryan, S.J., Sweeny, A.R., and Becker, D.J. (2022). Urban-adapted mammal species have more known pathogens. Nature Ecology & Evolution 6, 794–801. https://doi.org/10.1038/s41559-022-01723-0.
