Many companion bird species kept as single pets are flock-living species whose welfare requires either conspecific companionship or extremely intensive human social interaction to compensate.
Companion bird social welfare depends on species-specific needs that are often inadequately considered: a budgerigar kept alone in a cage with minimal human interaction is experiencing profound social deprivation for a species that naturally lives in flocks of hundreds. Parrots kept alone without intensive daily interaction develop feather destruction and compulsive behaviours. The welfare solution varies by species — some can be kept in compatible pairs, others require extensive human bonding — but single keeping with minimal interaction is rarely adequate for social species.