Feather damaging behaviour (also referred to as feather picking or feather plucking) is a behavioural disorder that is frequently encountered in captive parrots. This disorder has many characteristics that are similar to trichotillomania, an impulse control disorder in humans. Unfortunately, to date much of the information regarding the aetiology and treatment in both syndromes is based on [`]expert' opinion rather than on experimentally founded results. Comparative research in humans and parrots might therefore be mutually beneficial. Feather damaging behaviour (FDB) may also share similarities with behavioural disorders present in other bird species. Feather pecking (FP) in poultry is of particular interest in this case. Because of the major impacts on welfare and economy, the disorder has been thoroughly investigated. It has been shown that genetic, socio-environmental and neurobiological factors all play a role in FP. Several theories have been postulated about the different motivational systems that affect the behaviour, of which (redirected) foraging appears to be the most generally accepted. FDB may result from similar motivations and underlying mechanisms, but has also been regarded as a grooming disorder. Grooming or preening is behaviour that serves both physical and social purposes. In the presence of stressors, such as novelty, so-called displacement grooming may develop that can result in excessive grooming when chronic stress is experienced (maladaptive behaviour). Adrenocorticotropic hormone, opiate, dopaminergic and serotoninergic systems have been shown to influence the onset, development and maintenance of this behaviour. Primary brain dysfunction (malfunctional behaviour) may also explain the occurrence of various abnormal behaviours. Differences in neurotransmitter levels and distribution have been found between high and low feather pecking lines of laying hens, and psychopharmacological interventions in humans and parrots suggest similar alterations. The exact pathways via which neurotransmitters influence the execution of these behaviours have not been identified. It is also not clear which brain areas are involved in this dysfunction, and why the behaviour sometimes persists despite intervention. For these purposes it is important to consider the current system-level insights on different types of abnormal repetitive behaviour, to which these disorders may be classified.