To adapt to cities, birds must grow their brains or grow their families

March 25 (UPI) -- As the planet becomes increasingly urbanized, many species, including birds, are struggling to adapt to human presence. Urbanization can drive some bird species to extinction, but others are capable of thriving in cities.

New research -- published this week in the journal Frontiers in Ecology and Evolution -- suggests birds have a choice of two strategies for adapting to urban life. They can either grow bigger brains, or they can produce more offspring.

Better understanding how different bird species respond to human development can help policymakers craft more effective conservation and protection plans.

"Cities are harsh environments for most species and therefore often support much lower biodiversity than natural environments," lead study author Ferran Sayol, postdoctoral researcher at the University of Gothenburg in Sweden, said in a news release. "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."

Previous studies have shown bigger brains are advantageous for city life. Birds with more brain power are better at finding food sources and avoiding human hazards. But some small-brained birds, like pigeons, have also adapted quite well to urban settings. Until now, scientists weren't sure what accounted for the pigeon's success.

For the new study, scientists surveyed the characteristics of 629 bird species living in 27 cities all over the globe. Using scientific databases and museum collections, researchers compared the brain and body size, maximum lifespan, global distribution and breeding frequency of each of the species.

The analysis showed big brains are indeed to a boon for birds making their way in the city. But the data also revealed a second strategy.

"We've identified two distinct ways for bird species to become urban dwellers," Sayol said. "On the one hand, species with large brains, like crows or gulls, are common in cities because large brain size helps them deal with the challenges of a novel environment. On the other hand, we also found that small-brained species, like pigeons, can be highly successful if they have a high number of breeding attempts over their lifetimes."

The small-brained approach requires birds to sacrifice their longevity, their chance of survival, in order to produce more offspring.

In the wild, both survival strategies are rare. Likewise, birds with average-sized brains aren't often found in urban environs.

"In our study, we found a general pattern, but in the future, it could be interesting to understand the exact mechanisms behind it, for instance, which aspects of being intelligent are the most useful," Sayol said. "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."