The feralization process in the chickens on Kauai showed some extent of reversing domestication, by increased fear and anxiety related behaviour, decreased antagonistic behaviour and increased relative brain mass while changing brain composition compared to the domesticated chickens. The phenotypic differences between the feral chickens on Kauai compared to domesticated chickens reflect the adaptation to a wild environment where the chickens face natural and sexual selective forces. However, the feral chickens still show differences between ancestrous Red Junglefowl too, suggesting that feralization is more complex than simply reversing domestication.

Not all fear measures differed between feral and domesticated populations, plus there were also little to no correlations between the behavioural measures. The inconsistency in differences between the feral and domesticated populations and lack of relationships between multiple standardized anxiety- and fear-related tests suggest that these emotions have complex genetic architectures. 

The results also suggest a change in chicken brain mass and composition during the process of feralization. Increased relative brain mass in feral chickens could have evolved due to the increased importance for behavioural plasticity, for example, in a more complex, demanding and unpredictable environment compared to domesticated chickens living in captivity⁷. However, these forces might be more complex and case-specific as not all feral animals have increased brain size (e.g. pigs⁸) or at least not as big as their wild counterparts⁹.

High levels of variation in behaviour were found, especially in the feral chickens. This can be explained by the fact that we see a higher difference in coping styles in feral populations. Coping styles are generally divided between a proactive (bold) versus a reactive (shy) style, where a proactive coping style is associated with increased exploration, impulsivity, and activity, as opposed to decreased aggression and activity in a reactive coping style^{10, 11}. More pronounced differences in these coping styles are expected in feral and wild populations compared to domesticated popoulations, as reactive animals are easier to handle and thus thought to be selected for during domestication¹² .

Furthermore, differences in behaviour between the sexes is expected, as males that show higher vigilance¹³ and dominant displays^{13, 14} might increase their mating success and therefore be sexually selected for. Variation in behaviour can thus be explained by varying coping styles in response to stress, and differences between the sexes. 

The results reveal the complexity of behavioural and morphological changes that take place during feralization, as differences between ancestral, domesticated and feral chicken populations are observed. Just as domestication cannot be clearly generalised, as selection for desired traits is species specific, so is feralization unique per species and case. Feralization is an understudied tool to understand adaptation and evolution in a natural setting. Therefore, future research is encouraged to study feralization, which can have implications for evolutionary biology, conservation science, and animal welfare.