Stable individual differences in behaviour, termed personality in human psychology research, are increasingly also studied in animals. Especially the evolutionary mechanisms generating and maintaining individual differences as well as the functions and consequences of different personality types are still under debate.

We have developed a standardized test battery comprising three personality traits. We measured exploration in a novel environment, fearfulness in a tonic immobility test and aggression towards a mirror in a captive population of wild-type zebra finches (Taeniopygia guttata). Previous results showed that these traits represent independent, non-correlated personality axes and that they are repeatable across different ontogenetic stages (from subadults to mature adults) over a period of about one year.

We established bi-directional selection lines on each of these three traits to study their genetic and environmental causes as well as the covariation with fitness. Preliminary parent-offspring regression analyses indicated heritability estimates between 0.14 and 0.27 after the first generation of selection. Furthermore, we found a significant effect of selection line origin on juvenile survival to independence, with higher survival in lines selected on higher (bolder) trait values. We will report heritability estimates and fitness correlates obtained from the first three generations of selection.