Chickens use visual cues in social discrimination: an experiment with coloured lighting

In an experiment to investigate the cues used in social recognition by laying hens, visual cues were manipulated by altering the illumination. Hens from small flocks were allowed to choose to approach and feed next to a flockmate or an unfamiliar hen. The effect of dim and coloured lighting on this discrimination was investigated in a choice arena. The apparent brightness to the hens of three colour treatments (white, red and blue) were equalised at two brightness levels, comparable to the home pen (approximately 77 lux) and to conditions on a commercial farm (approximately 5.5 lux). On the basis of feeding preferences and aggressive interactions, hens discriminated between familiar and unfamiliar birds at levels above chance in only the bright white treatment. Subjects chose familiar hens over unfamiliar hens most frequently under white lights, and least often under red. Brightness did not significantly affect choice. Subjects' general activity (measured as either distance moved or time until a social choice was made) was unaffected by the lighting treatments. The results show for the first time that visual cues are important in social recognition in small flocks of laying hens. Possible implications for the welfare of hens kept under commercial conditions are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.