Figure 4. Acquisition of social attachment through the synchronised behaviour driven by a common motivation.

(a) Three Iso chicks met one another in the ‘school' cage as a mutual interaction (MI) on postnatal days 1–13 for 10 minutes per day with feeding (1), flying out of the cage (2), or neither (3). (b) At P14, the social test was performed. The results are summarised in the bottom columns. G, aa, E, and F designated g-move, active approach, escape, and freeze, respectively.