Much concern has been expressed about the negative effects of crowding in floor-housed and caged flocks with respect to air quality, disease incidence, and aggression. Crowding in both broilers and laying hens may lead to higher mortality and decreased growth and reproduction in individual birds, although overall economic returns from the flock may be greater (12, 13). However, there is little evidence to support the view that crowding increases aggression in broilers. Broilers are very docile and are also marketed at such an early age that they have not yet formed a dominance hierarchy (14).