Researchers in the Czech Republic and Germany have been looking through bird data from their countries around the fall of Communism.
Most of the factors appeared to affect bird populations similarly in the three regions. But brain size apparently made a big difference in the former communist nations: Birds with bigger brains tended to show a slight uptick in populations sizes in East Germany, and even bigger gains in the Czech Republic. The “increases of species with large brains suggest that species with good cognitive abilities might have been better able to adapt to rapid socioeconomic change and make use of novel opportunities after the end of communism,” the authors write.
The population gains might not be caused by brain size, but there’s at least a correlation there.