Influence of light/dark incubation on social behaviour in domestic chicks

Abstract

The aim of this study was to investigate the effect of light exposure during the last days of incubation on the social behaviour of domestic chickens. This exposure is known to lead to asymmetry in one of the visual pathways and to lateralization of visual behaviour. Day-old male chicks (White Leghorn x Australorp cross) were housed in groups of eight in three different treatments pre-hatching (six groups/treatment) 1) Dark; chicks incubated in dark during the last five days of incubation 2) Light; chicks exposed to light over the same period before hatching and 3) Mixed; four light and four dark incubated chicks. Each day from day three to seven social pecking was recorded (20 minutes/day) and competition for food was tested. On day nine a vigilance test was carried out where each group of chicks was exposed to an overhead image of a predator. We found no difference between the treatments in the amount of social pecking performed. The lowest ranking individuals in the Dark groups gained more access to food compared to the lowest ranking individuals in the Light and Mixed groups (P=0.041, F2,43=3.44), indicating that groups comprised of chicks without visual lateralization (Dark groups) had formed a less rigid social structure. More dark incubated chicks than light incubated chicks reacted the first time the image of the predator was presented (P=0.033, F2,15=4.30), but when tested in social isolation, dark-incubated chicks were less responsive to an overhead predator (Rogers et al., 2004, Proc. R. Soc. 271, s420-s422). These opposite results suggest that Dark chicks are more influenced by the social context than Light chicks. Differences between treatments implies that manipulating incubation conditions may be a means to improve welfare.