Apparently they selected for two lines of birds...one that had "exploratory" behavior and one that didn't, and found differences in DRD4 and they also found the same associations in free-living birds.
Update: For those who don't know, DRD4 is a pretty well known gene implicated in various behavioral phenotypes (ADHD) in humans, so the fact that they found it in birds is not so surprising, but good to know nonetheless.
They/we shoud look at DRD4 in the various domestic dogs and other canids.
Andrew E. Fidler, Kees van Oers, Piet J. Drent, Sylvia Kuhn, Jakob C. Mueller, Bart Kempenaers
Proceedings of the Royal Society London, B online before print
Abstract: Polymorphisms in several neurotransmitter-associated genes have been associated with variation in human personality traits. Among the more promising of such associations is that between the human dopamine receptor D4 gene (Drd4) variants and novelty-seeking behaviour. However, genetic epistasis, genotype–environment interactions and confounding environmental factors all act to obscure genotype–personality relationships. Such problems can be addressed by measuring personality under standardized conditions and by selection experiments, with both approaches only feasible with non-human animals. Looking for similar Drd4 genotype–personality associations in a free-living bird, the great tit (Parus major), we detected 73 polymorphisms (66 SNPs, 7 indels) in the P. major Drd4 orthologue. Two of the P. major Drd4 gene polymorphisms were investigated for evidence of association with novelty-seeking behaviour: a coding region synonymous single nucleotide polymorphism (SNP830) and a 15bp indel (ID15) located 5′ to the putative transcription initiation site. Frequencies of the three Drd4 SNP830 genotypes, but not the ID15 genotypes, differed significantly between two P. major lines selected over four generations for divergent levels of ‘early exploratory behaviour’ (EEB). Strong corroborating evidence for the significance of this finding comes from the analysis of free-living, unselected birds where we found a significant association between SNP830 genotypes and differing mean EEB levels. These findings suggest that an association between Drd4 gene polymorphisms and animal personality variation predates the divergence of the avian and mammalian lineages. Furthermore, this work heralds the possibility of following microevolutionary changes in frequencies of behaviourally relevant Drd4 polymorphisms within populations where natural selection acts differentially on different personality types.