How peck orders of chickens are measured: A critical review

The peck orders of chickens have been measured in many ways, and the question of which measure is most appropriate arises. This can only be answered in reference to the way that the measure is to be used. Staging paired contests between unacquainted birds is best used to assess the stable, intrinsic traits that underly dominance relationships. However, this method does not give reliable estimates of the relationships the birds form when grouped. The social environment of each bird is best assessed by observing the agonistic encounters that occur. However, the comparability of the different forms of aggressive behaviour needs to be established. Measures based upon priority of access to food cannot be used with confidence. Measures of rank need to be normally distributed and reflect the actual magnitude of the difference between birds only when these are to be used in assessing the underlying traits.