The main aim of the present study was to investigate whether the domestication process influenced the occurrence of play behaviour in chickens. Additional objectives were to characterise play in chicks by studying the ontogeny of play, and bring further knowledge on the biological function of play behaviour. In accordance with our hypothesis, when combining all play behaviours (both when including and excluding worm pecking), the White Leghorns were found to play more than the Red Junglefowls, indicating that, similar to other domesticated species, domestication increased playfulness in chickens. However, when looking at the grouped behaviours, the Red Junglefowls were found to perform more locomotor play behaviours and more play fighting, while the White Leghorns performed more object play behaviours. For most behaviours, contrary to our hypothesis, the occurrence peaked earlier and also decreased earlier for the White Leghorns compared to the Red Junglefowls. A significant interaction was found between breed and age for all grouped behaviours, indicating that the frequency of play behaviours changes differently over time in White Leghorns and Red Junglefowls.
Overall, our results agree with previous findings in species such as dogs, cats, mice and guinea pigs, confirming that domestication increased playfulness. However, the reason for the variation in which breed displays the highest frequency of play, depending on behaviour, is not as straightforward.
When comparing the overall occurrence of play, it seems as if domestication have affected play behaviour, in the sense of increasing its frequency. However, when comparing the occurrence of the behaviours grouped and individually, variations in which breed plays the most are observed, and the pattern is not as clear. Whether all behaviours observed in the present study should in fact be considered play behaviours cannot yet be determined, an aspect that potentially could generate a different outcome of future studies with the same objective. The present study can be used as a basis for the development of future studies, investigating the occurrence and function of play behaviour further, with a refined experimental set-up. The information about ontogeny of play behaviour gained can be helpful in future studies on the play-welfare relationship.