Some birds avoid cities, but others purposefully move to them, seeking their own version of the big time.
Birds that do best in cities tend to have big brains.
Larger brains allow birds to adapt to different foods, habitats and other changes required of city life.
Urban sprawl is threatening less brainy birds that do not cope well in novel environments.
The brainier a bird is, the better its chances are of thriving in a city, according to a new study that found many big-brained birds can succeed in urban environments.
"Big" in this case refers to brain size relative to body size. In other words, the larger the ratio of brain to body, the more likely the bird will thrive in an urban environment.
"Species with relatively larger brains tend to have broader diets, live in diverse habitats and have a higher propensity for behavioral innovations in foraging," lead author Alexei Maklakov told Discovery News. "They are better able to establish viable populations when introduced to new habitats by humans."
Maklakov, a researcher in the Department of Animal Ecology at Uppsala University, and his colleagues studied how well -- or not -- 82 species of passerine birds belonging to 22 avian families did in and around a dozen cities in France and Switzerland.
Bird species that were able to breed in city centers were considered successful colonizers. Birds that bred around the cities, but not in the urban regions themselves, were considered to be urban avoiders.
For the study, which is published in the latest issue of Royal Society Biology Letters, the scientists also looked at the brain size and body mass of each bird.
The researchers determined that the following are brainy birds that do well in cities: the great tit, the blue tit, the carrion crow, the jackdaw, the magpie, the nuthatch, the wren, the long-tailed tit and more. Pigeons are not passerines, so these ubiquitous urban dwellers were not included in the study.
While pigeons are smart, they are not necessarily the Einsteins of the bird world. "Pigeons probably represent a great example of a bird for which we inadvertently created a fantastic replica of their original habitat with plenty of nesting places, near lack of predators, and an ample food supply," Maklakov explained.
The study determined the following bird species with relatively small brains are avoiding city centers: the yellowhammer, the reed bunting, the whitethroat, the lesser whitethroat, the pied flycatcher, the golden oriole and additional birds.
Brain size isn't always an indicator of intelligence, so these smaller-brained birds aren't stupid. Some insects, for example, have extremely tiny brains and yet are quite behaviorally complex. Neanderthals are even thought to have had larger brains than humans do today.
The answer could be that increased brain size in birds is tied to certain key brain structures that allow for innovation and change.
We might even be making big-brained birds brainier.
While urban adapters are more likely to come from large-brained families, suggesting this trait evolved before the emergence of our cities, "it is not impossible that novel selection pressures might, in theory, lead to the evolution of brain morphology in urban populations," Maklakov explained.
Cities increasingly dominate the planet, with predictions that by the year 2030, the number of people who dwell in cities will increase by 1.75 billion. So where can a small-brained, urban-loathing bird go?
Maklakov suggests that conservationists and city planners "create patches that closely resemble (these birds') original habitats within city boundaries."within Daniel Sol is a researcher at the Autonomous University of Barcelona's Center for Ecological Research and Forestry Applications.
"I think it makes a lot of sense that the success of some birds in highly urbanized environments is related to their larger brain and enhanced behavioral plasticity, as the cities provide a variety of ecological opportunities that require changes in behavior in order to be exploited," Sol told Discovery News.
"Other authors have tested this idea before, but the present study is the first to provide evidence for this to be the case," Sol added.
In the future, additional investigations could shed light on exactly how the brains of birds are structured. Scientists might also investigate whether humans have the power to make birds brainier, which would require comparing urban and non-urban populations of the same species.