Cities aren’t known for their booming biodiversity, but some animals stand out as A+ urban dwellers, and birds may be number one.
Now, scientists are starting to understand just how pigeons and other birds have evolved strategies enabling them to survive and thrive in cities around the world.
Despite the lack of trees, and the surplus of people, birds have an uncanny ability to survive the bustling concrete jungle.
In a new study, researchers narrow down their expert survival skills to two strategies:
1. Brain power: Birds with large, well-developed brains, like crows and gulls, use their brain power to help them navigate the city streets.
2. Breeding power: Pigeons and other, smaller-brained bird species reproduce more frequently to improve the chances that their progeny will make it to adulthood.
Researchers dug into data from 27 cities worldwide, looking at more than 600 species of birds, to figure out how birds are able to thrive among the pavement. They studied factors like brain and body size, lifespan, population distribution, and breeding habits.
The idea that large-brained birds have an edge on other animals isn’t new — research shows some parrot species' intelligence rivals that of human babies, after all. In a study published in March 2020, for example, kea parrots were able to understand the concept of probability, predicting how likely a researcher's actions would result in them getting food. These skills come in handy living in a place densely populated with humans.
By contrast, pigeons, synonymous with cities, aren’t known for being particularly intelligent. For these relatively small-brained birds, ramping up breeding frequency is key.
Each of these strategies is specific to city living — the same isn't seen in more wild areas, the researchers say. Rather, the findings suggest that these survival strategies are distinct — birds with average-sized brains are the least likely to be found in cities.
"The species that can tolerate cities are important because they are the ones that most humans will have contact with in their daily lives, and they can have important effects on the urban environment within our cities," he said.
In turn, the research helps to inform us about how cities influence the nature they replace.
"Understanding what makes some species better able to tolerate or even exploit cities will help researchers anticipate how biodiversity will respond as cities continue to expand," Sayol said.
Abstract: Urbanization is a major driver of local biodiversity losses, but the traits that determine whether species are able to tolerate urban environments remain poorly understood. Theory suggests that a larger brain should provide higher tolerance to urbanization by enhancing behavioral flexibility to cope with novel challenges. However, assembling empirical evidence for a link between brain size and tolerance to urbanization has proven to be difficult, perhaps because the effect of the brain interacts with life history to influence persistence in urban environments. Here, we provide a global-scale assessment of the role of brain size on urban tolerance, combining quantitative estimations of urban tolerance with detailed information on brain size, life history and ecology for 629 avian species across 27 cities. Our analysis confirms the expected positive association between brain size and urban tolerance, but shows that the relationship is more complex than previously shown. While a large relative brain size generally increases urban tolerance, species with small brains can still attain high success in urban environments if they spread the risk of reproduction in multiple events (i.e. have a low brood value). These alternative strategies, although uncommon in natural conditions, seem to be favored in urban environments, fundamentally restructuring the composition of urban communities. Thus, our results support the notion that brain size mediates tolerance to urbanization, but also shows that there are alternative ways of exploiting urban environments. Our findings reconcile previous conflicting results regarding the effect of brain size on urban tolerance, and provide the basis for improved predictions of the responses of organisms to increasing urbanization over the coming decades.