Feather pecking in replacement breeders (young birds reared to become breeding stock, especially chickens and turkeys) is a multifactorial behavioural problem. The main causes are usually grouped into management, nutrition, environment, genetics, and social stress factors.

Here are the primary reasons:

Overcrowding and high stocking density.

Too many birds in limited space increases stress and frustration.

Birds cannot escape aggressive individuals, leading to pecking escalation.

Nutritional deficiencies or imbalances. Low protein levels, amino acid deficiencies (especially methionine and lysine), salt deficiency, or inadequate fiber can trigger abnormal pecking.

Hunger or feed restriction in breeder birds is a major contributor.

Poor environmental conditions.

Lack of litter, pecking materials, perches, or stimulation redirects pecking toward flock mates’ feathers.

Lighting problems. Excessively bright light increases activity and aggression. Sudden light changes or improper light programmes can also contribute.

Stress and fear. Handling stress, temperature fluctuations, noise, poor ventilation, or sudden changes in routine increase feather pecking behaviour.

Genetic predisposition. Some strains are more prone to nervousness and feather pecking than others. Selection for high productivity sometimes increases behavioural problems.

Poor litter quality. Wet, caked, or insufficient litter reduces natural scratching and foraging behaviour. Birds then redirect pecking to flock mates.

Social instability. Mixing groups, uneven flock size, or frequent movement of birds disrupts hierarchy and can increase pecking.

Disease and parasite irritation.

External parasites, skin irritation, pain, or illness can attract pecking from other birds.

Sick or weak birds are often targeted.