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This is Scientific American's 60-second Science. I'm Suzanne Bard.

As long as humans have been building cities, wildlife has been fleeing from them.

After all, cities are noisy, crowded, and dangerous for animals, including many birds.

But we know that some birds do very well in urban areas.

So in many cities we have pigeons or doves, any kind of crow species.

University of Gothenburg biologist Faran Sayal. He and his colleagues are interested

in why some birds thrive in urban environments. They suspected that having a large brain in relation to

overall body size could be an advantage. Having a big brain give you more behavioral flexibility.

So, for instance, in cities, maybe these big brain species are better able to identify

opportunities for finding food, also to identify dangers in the city.

But this scenario doesn't account for birds like pigeons,

which are decidedly lacking in the brain power department.

Ceyal and his colleagues analyzed the relative brain sizes of 629 bird species

from 27 cities around the world, as well as their tolerance for

urban life. They found that birds that flourish in cities come into extremes. They're either

big-brained but produce few offspring over their lifetime, or they're small-brained and super-fertile.

So then this means that we have these two opposing strategies.

...