The domestic chick became a model for understanding memory, learning and the onset of social behaviours. Just after hatching and for a limited period, the naïve bird seeks a suitable object to imprint. Thanks to laboratory studies, the filial imprinting has been well documented in the very first few hours. However, how the filial imprinting preferences develop and evolve over time remained relatively unexplored. Therefore, we built an automated setup allowing us to follow the animal behaviour across prolonged durations and investigate the stability and variability of filial imprinting preferences. We demonstrated that three days of exposure to artificial objects produce lasting and robust imprinting preferences. With lower imprinting duration, we found that the animal predispositions strongly influence the filial imprinting preferences. Those social predispositions guide the domestic chicks towards living creatures – or at least, towards stimuli conveying animacy. To complete this general pattern, we performed two experiments manipulating motion dynamics. We showed that chicks prefer quickly rotating objects and agents moving with unpredictable temporal sequences: two cues probably used to detect living animals' presence. Both imprinting and social predispositions influence each other, but whether they share a neurophysiological ground was yet to be described. Such as for filial imprinting, we showed that the thyroid hormone T3 strongly affects the sensitive period for animacy preference. T3-inhibition closes the sensitive period for animacy preference and T3-injections re-opens it. Altogether, the present thesis complete previous research on filial imprinting and social predispositions: two distinct but interconnected mechanisms that can help to better understand the mind foundations at the onset of life.

Filial imprinting is a type of early developmental learning in which certain species buildstrong and mostly irreversible connections to objects or individuals. These connections couldbe shaped by the contribution of several stimuli including the fragments of auditory and visual components. This study aims to describe the duration of the imprinting process as well asestimate long-term behavioural changes in chicks. In this experiment, a total of 78 chicks were used out of which 39 were exposed to imprinting stimuli and the rest served as control.We applied three different tests and replicated them after the imprinting procedure. These tests are Imprinting Preference Test, Social Preference Test and Social isolation Test. Imprinted chicks had a constantly shorter latency to approach the imprinting stimuli for boththose two experiments with or without novel objects, whereas no preferences spent time inimprinting stimuli. However, introducing a novel object affected imprinting preferences more in terms of spending a longer time around the hen zone. During social isolation, the control group showed a relatively higher rate of distress calls even though our results don’t bear on the significant effect of filial imprinting on changes in distress calling. Overall, this study suggests the presence of long-lasting filial imprinting that is more triggered by external situations.

In layer hen commercial production systems, chicks are not raised by hens and do therefore not receive any maternal care. In the wild, after hatching, chicks undergo filial imprinting where they create a social bond with a stimulus in their surrounding environment, usually the mother hen. Filial imprinting behaviors remain in chicks until adulthood. This bond and maternal care influence the emotional development of chicks. Here, I aimed to investigate short- and long-term effects of filial imprinting on a model hen, on the emotional state of White Leghorn chicks, hatched at Linköping University. To measure optimism, pessimism, and fear, a judgment bias test (JBT), an open field test (OFT), and a novel object test (NOT), was performed and replicated. Before the tests, half of the chicks were imprinted on a model hen, while the other half was not given such a model to imprint on. All chicks were weighed during the entire project. The hypotheses were that the imprinted chicks would be more optimistic in the JBT, show less fearful behavior in the OFT and NOT, and weigh more compared to the non-imprinted chicks. If these results would be found, imprinting could potentially be used to reduce stress in commercially hatched chicks, and thus improve their welfare. The results were inconsistent with all three hypotheses. This indicates that imprinting on a model hen, did not have a positive impact on the chicks’ emotional state. Further studies need to be performed to find methods to improve commercially hatched chicks’ emotional welfare.