Stability and individual variability of social attachment in imprinting

Filial imprinting has become a model for understanding memory, learning and social behaviour in neonate animals. This fast attachment mechanism allows the young of precocial bird species to learn the characteristics of conspicuous visual stimuli and display affiliative response to them. Although more prolonged exposure to an object produces a stronger preference for it afterwards, this relation is not linear. Chicks can even prefer to approach novel rather than familiar objects at some stages of imprinting. The time course and stability of imprinting has just started to be investigated. To date, little is known about how filial preferences develop across time, due to the challenges in assessing individual performance. This study aimed to investigate filial preferences for familiar and novel imprinting objects over time. We have used an automated setup to track the behaviour of chicks continuously for subsequent days. After hatching, chicks were individually placed in an arena where stimuli were displayed on two opposite screens. The duration of exposure and the type of stimuli were manipulated while the time spent at the imprinting stimulus was monitored across six days. We showed that prolonged exposure (3 days vs 1 day) to a stimulus produced robust filial imprinting preferences. Interestingly, with a shorter exposure (1 day), animals re-evaluated their filial preferences in functions of their innate preferences and past experiences. Our study suggests that predispositions influence learning when the imprinting memories are not fully consolidated, driving animal preferences toward more predisposed stimuli.