Behavioural development of birds is shaped by the complex interplay between genetics and environment. It is becoming increasingly clear that experiences of previous generations are transferred to the offspring through epigenetic and hormonal effects and result in lasting changes in behaviour. After hatching, social and physical conditions during early life have marked effects on bird behaviour of both the current and following generations. Aspects like the presence or absence of maternal care, the composition of the social environment and the behavioural stimulation offered by the physical environment all have strong influences on the behavioural development of a bird. Research approaches that focus on manipulations during the early-life period and investigate effects on epigenetics, maternal hormones and behavioural development should be encouraged.