Prenatal light exposure affects early feather-pecking behaviour in the domestic chick

Recently we proposed that early feather pecking is a form of social exploration. Social recognition, important for exploration, is a lateralized function in the domestic chick. Lateralization of functions can be influenced by light exposure late in embryonic development. Therefore, we investigated whether this light exposure affected early posthatching feather-pecking behaviour in domestic chicks, Gallus gallus domesticus. White leghorn embryos either were exposed to light or remained in darkness in the last week of incubation. After hatching, they were housed in groups of two light-exposed and two dark-incubated chicks. Light-exposed chicks showed more feather pecking than did their dark-incubated cagemates. Dark-incubated chicks preferred to direct feather pecks to unfamiliar peers than to familiar peers; light-exposed chicks showed no preference. These effects were present in the first week after hatching and remained at least another 3 weeks. These results support the hypothesis that early gentle feather pecking is part of the normal behavioural repertoire of young chicks and influences social exploration. We discuss a possible mechanism underlying these results. We also suggest that it may be worthwhile not to expose embryos to light during the last week of incubation when housing hatchlings in commercial conditions, where feather pecking is a serious problem. [PUBLICATION ABSTRACT]