Head size and personality in great tits Parus major

Abstract

Behavior and decision–making depend on cognitive abilities and ultimately brain size and structure. I hypothesized that personality may be related to relative brain size adjusted for body size, and therefore, that selection acts against individuals that have small brains for their body size. I investigated standard personality scores in great tits Parus major from the field in relation to head volume, sex, age, capture date, and body size. Head volume and brain mass were strongly positively correlated, allowing for non–destructive estimation of brain size based on head volume. Personality score was positively correlated with head volume andwas higher in individuals captured later in the season. In an analysis of head volume in relation to sex, age, date of capture and body size, males had larger heads than females and older individuals had larger heads than yearlings. Head volume was larger in individuals captured later during the season. These findings are consistent with the prediction that personality is related to relative brain size and that selection acts on personality and relative head size as reflected by changes over time and between age classes.