As it turns out, birds can learn road speed limits, adapt to the direction of traffic and use road networks to help navigate their own flight journeys. Despite birds using and learning the complexities of human roads, however, there are roughly a quarter of a billion birds killed by traffic annually across the world each year. Møller and Erritzøe suggest that the birds that are killed by traffic are those with smaller brains. The theory is that larger brain sizes allow birds to adapt better to road traffic and, therefore, reduce their chances of being hit by a moving vehicle.
Using statistical techniques, Møller and Erritzøe analysed the link between 3521 birds being killed by traffic and their relative brain mass. They found that birds that were killed in traffic indeed had relatively smaller brains, with no similar difference for liver, heart or lung mass.
If only our brain sizes were large enough for us to figure out just what anyone is going to do with this information.