Bird-brains at the small end of the scale stand a greater chance of being shot, a study has found.
Scientists found a strong correlation between the size of birds' brains and the likelihood of them being killed by human hunters.
The team speculates that shooting enthusiasts could be having a Darwinistic effect on bird evolution.
According to the theory, hunted species should become bigger-brained, smarter and better able to escape the guns than protected species.
Each year, many millions of mammals and birds are killed for sport.
The aim of the research was to see if there was any evidence that having a bigger brain contributed to survival among hunted species.
Analysis of a large Danish database of birds showed a 30-fold difference in risk of getting shot associated with an almost 87-fold difference in brain mass.
The chances of being shot fell from 29 per cent in birds with brains weighing an average of 0.23g to just 1 per cent in birds with a brain mass of just under 20g.
Larger body size also increased the likelihood of being shot, but this was accounted for by the researchers.
The scientists, led by Dr Anders Moller, from the University of South Paris, France, wrote in the Royal Society journal Biology Letters: "The findings reported here have a number of implications for studies of brain size.
"First, hunted and protected populations of the same species should differ in brain mass with the former having larger brains.
"Second, we also hypothesise that if there are costs associated with an increase of brain size in hunted species, such as increased metabolic costs or increased use of antioxidants during brain development, this could potentially change the bias in brain mass in hunted compared to protected species.
"In conclusion, hunting selects for increased brain mass in birds, and this effect is independent of a number of potentially confounding variables, such as age, body condition, sex and body mass."