Light intensity and social communication between hens

1. The effect of light intensity on social communication in laying hens was investigated experimentally by comparing the transmission and detection of social signals between familiar and unfamiliar hens of similar or unequal rank in a competition for food. 2. The experimental method consisted of mutual inspection by a pair of hens at short range (approximately 24 cm), followed by a competition at a feed trough from which only one hen could eat a favoured food. The relative rank of a hen was inferred from success in this competition. 3. The relative rank of individual hens within 5 groups, each of 6 adult laying hens, was determined to identify those of high and low rank within their home group. 4 Social communication between pairs of either unfamiliar or familiar hens of either similar or unequal rank (highest and lowest ranking within their home groups) was then assessed under light intensities of 1, 5, 20 and 100 lux with all other cues present. Only the dimmest light of 1 lux perturbed some aspects of the competition for food. 5. The findings provide scientific justification, in part, for the current legal requirement in England for 'all hens to see other hens' by specifying a minimum light intensity of at least 5 lux for hens kept in close proximity to each other.