Is there a connection between urbanization and intelligence in birds?
This question has long been a subject of debate in biology. One theory has been that city birds are the species with the largest brains, because they are the ones who have managed to adapt to a new environment.
Bigger brains, bigger success?
– It has previously been thought that bird brain size is related to success, because bigger brains may ensure that they are more innovative and flexible, says Professor Svein Dale of the Norwegian University of Life Sciences (NMBU).
– For example, by taking advantage of new food resources, and avoid new enemies and human disturbances.
In short: the bigger the brains, the better the adaptability.
Large and small bird brains
Researchers have recorded birds in parks, cemeteries and green areas in Oslo and looked at the relationships between habitat and several different biological and ecological factors, including brain size.
In addition, they gathered data on a factor that previous studies have largely ignored: How common are the bird species outside of the city?
The average bird brain in this study weighed 2.12 grams, of which the smallest weighed 0.31 grams and the largest a whopping 15.31 grams. It turned out, however, that size does not matter.
– Our research shows that brain size has no influence on whether or not birds are part of the urban landscape.
Common in the countryside, common in the city
The results suggest that urban bird communities are mainly determined by how common the species are in the surrounding countryside outside the city, and what kind of habitat and nest location they have. Brain size has no effect. This was confirmed through further analyses of published data from six European cities.
– It is the bird species that are common outside of the city, who are urban, not those with big brains, says Dale.
Green areas are important
Although Oslo's cityscape is characterized by numerous bird species - 60 registered in this study - there are few species that exclusively live in the city.
– The number of bird species that are fully adapted to city life, is low. This means the number of city birds depends on how much diversity there is in areas outside of the city. These birds can then fly into town and make it more diverse, says Dale.
Naturally, the presence of green areas in the city is also very important.
– One can compare green areas in the city with oases, where the buildings around constitute an unappealing desert. Our findings can help planners and wildlife managers to better understand how the urban bird diversity can be maintained and increased, says Dale.
Svein Dale, Jan T Lifjeld og Melissah Rowe: Commonness and ecology, but not bigger brains, predict urban living in birds, BMC Ecology, april 2015,