The impact of domestication on fearfulness: a comparison of tonic immobility reactions in wild and domesticated finches.

We examined differences in the fear response between Bengalese finches and their wild ancestor, the white-backed munia, to explore the evolutionary mechanisms of behavioural changes due to domestication. The Bengalese finch (Lonchura striata var. domestica) was domesticated from the wild-living white-backed munia (L. striata) approximately 250 years ago. A previous study indicated that Bengalese finches sing much more complex songs than white-backed munias. We hypothesised that Bengalese finches are likely able to allocate more resources to reproduction in exchange for reduced survival effort. We measured tonic immobility (TI) reactions as a response to physical restraint to evaluate fearfulness related to coping with predation. The results showed that Bengalese finches exhibited decreased TI responses compared with white-backed munias. TI responses were unaffected by sex, body weight or growth conditions. These differences suggest that the fearfulness in Bengalese finches has been reduced by selective pressure during domestication. Bengalese finches may have been able to increase the investment of energy in reproduction in exchange for reduced costs of predation and coping necessary to survive in the wild; these behavioural changes may have been a major target of domestication effects in this species.