Behavioural consequences of visual deprivation occurring at hatch or in the early life of chickens

The development of behaviour in a line of chickens that are born sighted (rdd) but turn blind after hatching was compared with a line that is blind at hatch (beg) and with sighted White Leghorn controls (WL) to test the hypothesis that birds that become blind later in their life will show characteristic behaviours of both blind and sighted birds. Individual behaviour, group aggregation and behavioural synchrony were compared at 1, 5 and 9 weeks of age (experiment 1) and in the parents of these chicks at 9-13 months of age (experiment 2). Responses to visual and physical isolation were assessed at 1, 5 and 9 weeks.Analyses of home-pen behaviour showed that both rdd and beg had difficulty locating or consuming food during the first week of life. WL and rdd did not engage in abnormal behaviour (circle walking, air pecking, star gazing) at 1, 5 and 9 weeks whereas both beg and rdd adults did so. At 9 weeks beg and rdd birds showed decreased behavioural synchrony compared with WL, whereas group aggregation in rdd and WL was similar and higher than in beg. WL adults showed increased environmental pecking and higher rates of behavioural synchrony and group aggregation than both beg and rdd. Under visual isolation from conspecifics rdd chicks behaved like blind birds in some respects (e.g. decreased movement) and as sighted birds in others (e.g. peeping). The vision of rdd was apparently diminished compared with sighted controls (WL) even from an early age.It was concluded that abnormal behaviours are a response to a complete loss of vision regardless of initial sight. Birds that became blind during rearing (rdd) may be more active as adults than birds that were blind throughout life but in general the behaviour of blind birds was similar regardless of early sight.