Low incidence of aggression in large flocks of laying hens

In a series of experiments to investigate the social relationships of domestic hens in large flocks the incidence of agonistic interactions was determined in a free range system with 700 birds and in a perchery system with ten 300-bird flocks. In both systems aggressive behaviour was infrequent and, in general, rates of agonistic interaction per bird per hour were markedly lower than those previously reported for laying hens kept in small to moderate group sizes. In the perchery, when the doors between adjacent pens of 300 laying hens were opened, previously separate flocks mixed together without any apparent evidence of increased aggression. This is in contrast to what has been reported for smaller groups, which when allowed to mix fought and failed to integrate. When sub-groups of six birds were taken from the large flocks and mixed in a separate pen with six birds from other flocks or from their own flock as a control, agonistic interactions were again rare in both conditions. It is proposed that, in general, there is no individual recognition in large flocks: birds do not recognise flockmates as 'familiar', nor birds from other flocks as 'unfamiliar'. This apparent lack of social structure in large flocks may be a factor in minimising agonistic interactions between individuals, with a consequent low level of aggression compared with smaller groups where there is an established hierarchy. (C) 1997 Elsevier Science B.V.