Linköping University is home to one of the very few breeding populations of red junglefowl that exists outside of the wild. Multiple labs within their biology department use the population to learn more about the physiology, behavior, and genetic background of the species, and to compare them to their descendant, the domestic chicken.
In a recent publication, one of their labs has shown that selection for less fearful, more domestic birds changes the overall brain size of the population! After ten generations of selection by researchers, total brain mass increased, but relative to the overall body size (which increased a great deal), the percentage of body weight that was brain decreased! This size change is similar to the difference seen in domestic chickens (which have much larger body sizes, but smaller relative brains than red junglefowl), hinting at a possible link between brain size and behavior.
Read more about the study here!