Body size and fluctuating asymmetry in relation to cannibalistic behaviour in laying hens

We studied cannibalism in laying hens, Gallus gallus domesticus. From farms experiencing high mortality caused by cannibalism we collected cannibalistic birds, birds with injuries caused by pecking and control birds. All factors such as farm, bird hybrid and age were identical within a set of three birds, but differed between trios. Based on predictions from studies on wild animals, we hypothesized that cannibalistic laying hens would be larger and victims smaller than control birds, and that victims would in some way be less fit than control birds. In addition, since cannibalism in the wild is usually shown by individuals under adverse conditions, we hypothesized further that under commercial conditions cannibalistic individuals would be those that experience the environment as more stressful than others in the flock. Since fluctuating asymmetry is thought to be positively correlated with low stress-buffering capacity, we expected cannibals and victims to be more asymmetrical than other birds. As predicted, cannibals were heavier and taller than other birds and both victims and cannibals were more asymmetrical than control birds. (C) 2001 The Association for the Study of Animal Behaviour.