Aggression and feather pecking or plucking are the two most common behavioral problems in chickens. They may be related and possibly have similar underlying components, including stress, overcrowding, and competition over resources such as food. Both conditions can be managed by addressing the underlying problem and in some cases by removing the instigator. Providing enrichment and changing the social structure by removing or adding individuals may help as well. In rare cases, aggression can advance to cannibalism (see Cannibalism in Poultry). Broilers and free-ranging chickens are more likely to show these problems because egg-laying chickens in mass production are usually confined to small groups.
Aggression can manifest as pecking at the head and face or as pecking at and pulling feathers. Chickens have sharp and strong beaks that may lead to severe injuries. Reducing daylight in battery conditions, adding tryptophan to the food, and beak trimming can minimize aggression. Beak trimming is a symptomatic treatment, however, and may raise welfare concerns.
Grooming and feather care are part of normal hygiene in chickens and can also be social activities. Dust baths can help reduce the incidence of feather picking.