Pecking order

See also Dominance (animal behavior)

Referred to as the pecking order, dominance hierarchies in chickens is asserted by various behaviours, including pecking, which was used by Schjelderup-Ebbe as a measure of dominance and leadership order in his 1924 German-language article. He noted that "defense and aggression in the hen is accomplished with the beak". This emphasis on pecking led many subsequent studies on fowl behaviour to use it as a primary observation, however, it has been noted that roosters tend to leap and use their claws in conflicts.

The basic concept behind the establishment of the pecking order among, for example, chickens, is that it is necessary to determine who is the 'top chicken,' the 'bottom chicken' and where all the rest fit in between. The establishment of the dominance hierarchy may reduce the incidence of conflict and thus reduce the expenditure of energy required for aggressive competition. The dominance level determines which individual gets preferential access to resources such as food and mates.

In the wild, pecking order status is inherited along a strict basis, so that the first daughter of the most dominant chicken will inherit that most dominant status, the second most dominant will give second most dominant status to her daughter, etc. unless the most dominant chicken has a second daughter, in which case that chicken will become the second most dominant. Studies of the genetic basis of pecking orders in chickens have indicated that it may largely be determined by the coloration patterns.

It is not necessary for animals to be able to recognise individuals within the group for a pecking order to be maintained. Animal behaviours may be motivated by "rule of thumb". For example, if chickens can predict the fighting ability of others simply by assessing their body size, they will be able to maintain the hierarchy whilst avoiding a fight which could cause injury and will be energetically costly. Using this rule of thumb, if Chicken A sees that Chicken B is larger, Chicken A will defer; if Chicken B is smaller, it will defer to Chicken A. In this way, only chickens of similar sizes will fight and the pecking order of the group overall is maintained without requiring individual recognition.

Wild and feral chickens form relatively small groups, usually including no more than 10 to 20 individuals. It has been shown that in larger groups, which is common in farming, the dominance hierarchy becomes less stable and aggression increases.